electrical budget??

[haulback]

OK so I finally took a look at the electrical budget worksheet.......I will of course fill in some of the blanks but only hope that this is the kind of test I cannot 'fail' !!!

However, as I see it I can not (truthfully) complete this to reflect what may, or may not, get either consumed or produced while sailing from San Francisco to Hanalei.
-Which drive unit am I going to use with the AP??
-Or will the windvane happily steer the boat all the way?
-What will cloud cover be, and how much will my new solar array REALLY produce.
-Maybe they will get washed off the boat again??
-I trust engine will start and alternator charge when requested, but maybe they won't.....

I do not question the purpose of the worksheet, (probably a good way to make people think about their electrical usage) but wonder at the necessity of inflicting it upon this group of sailors. Everyone, I am sure, is aware that whatever power they consume must be somehow replaced - but this is only common sense and anyone whom has gone far enough down the road to get to the beginning of this event must have already figured that out for themselves.

Isn't that what the qualifying cruise is supposed to get them started thinking about???

What may be more helpful is to ask them what they will do if the on-board electrical system suffers catastrophic failure halfway there - then what??? They lose charging ability, storage capacity, or suffer an electrical fire.... A lightning strike, anyone???

Do they have a plan for that???? How exactly do they get the boat across a thousand miles of ocean and find a safe harbour - at that point, probably not even Hanalei Bay??

Surely they must have a workable solution to this scenario apart from pulling the string on the EBIRP??? Yet without a little foresight, planning and the right equipment available, perhaps that may be what some would resort to.....

Comments????

Jim/Haulback

 

[Alchera]

I think you're right, I don't think you can 'fail' the energy worksheet except by failing to fill it out. I have yet to fill mine out, I'm getting my alternator repaired and don't know how the repaired unit is going to work until I try it out. Seems the old one got overheated at some point and the windings degraded, or so I'm told.

But you raise a couple of interesting points. How would we cope with *total* electrical failure, as from a lightning strike which fries every electronic piece of equipment, handheld or not. At that point even navigating becomes difficult, no distance or speed log (how many of us are going to carry a backup taffrail log?), no time signals even if you happen to have a sextant. (Head south until you get to the proper latitude then go west, just like the old time sailing ships before accurate longitude!). Hopefully everyone is carrying their required non-electronic compass. (I wonder if a lighting strike can wipe out the magnetized needle?)

I carry a backup handheld GPS wrapped in tinfoil (Faraday cage) and in a waterproof container so hopefully even in the worst circumstance it will still work, but who knows? I seem to recall Tiger Beetle uses his oven as a Faraday cage for handhelds, which also sounds like a good idea unless you decide to preheat it without checking inside first!

As for the EPIRB, another good question. I don't think I would ever set one off unless I was sitting in the liferaft and the boat was at the bottom. But I wonder, when do you notify the coast guard you are having problems and may be in danger? If I'm on a boat that may go down at any second, it would be nice to have the coast guard know where my last position was in case the EPIRB fails. On the other hand, as long as there's a chance of saving the boat, I don't want the coast guard to show up and start demanding to 'rescue' me. I'm sure it's somewhat of a catch-22 for the coast guard as well, since they could be accused of being negligent if they don't respond and someone loses their life as a result.

I seem to recall one of the previous TransPacs, where a competitor lost use of her SSB and couldn't be accounted for for several days. Someone shoreside overreacted, saying we had 'lost contact' with one of our racers and notified the coast guard. The coast guard then started making noises about search and rescue. At least that's vaguely how I remember the story. But you can see how the coast guard can be put in a position of 'damned if you do, damned if you don't', and is going to err on the side of overreacting, rather than underreacting. So it's something to keep in mind before making a call.

- Mark

 

[AlanH]

Hmmm...."Faraday Cage" I wonder if an old metal (unused) paint can would work as a Faraday Cage for my backup GPS and the handheld radio.

A lightning strike CAN destroy a magnetic compass. Also a lightning strike can magnetize a lot of the previously non-magnetic metal in the boat, thereby making the compass act totally whacked out. This happens in airplanes pretty often.

Windvanes don't depend upon electrons to steer. That's the REAL reason I use one.

As for the electrical budget, I think Jim has a point, but on the other hand the RC needs to go to some sort of lengths to ensure that people have at least thought about major issues, and filling out the form and seeing if there's some glaring discrepancy can't hurt. It's pretty painless. Of course, it only makes sense to have backups.

Regarding electrical systems....I've said this a million times so here goes a million and one. In 1996 I got to Hanalei on two fully charged batteries and a four-hour charge run with my Lightning generator on about day 12. I had no solar panels. I carried a LOT of AA and C batteries!

The GPS's were all handhelds.
The Navik windvane did the steering.
I didn't use Navigation lights, but I did have a masthead strobe.
Other strobes in the rigging were armband strobes.
I didn't talk to anybody for 16 days on the radio.
I essentially never ran cabin lights.

That taught me a lesson. You can go a LONG way with a totally dead house electrical system if you just have independent systems that don't depend on house electrons to run the boat.

 

[blighbaum]

Are lightening storms common in July where we'll be going? Is this like sailing back East in the summer?

- Tom K Feral

 

[ScottJ]

Faraday Cages

You guys have probably already discussed this, but I just can't find where so I'll throw this in for redundancy. Faraday cages are shaped like that diamond plate screen thing that hangs in your paint bucket to roll off the excess paint. Your best/cheapest protection available against lightning are the anti-static-faraday bags we use to ship motherboards and hard drives. If you go into any local computer shop that builds computers, they've got these laying all over the place and you should be able to pick up 3-5 at $2-3 ea(max) if not FREE. Double bagging a spare GPS in these before putting into a waterproof, all vinyl, no metal bag, while not clipping it to anything metal on the boat is your safest protection against lightning, static, RFI signals, or EMP. Remember there are 2 kinds of anti-static bags. The mirror-mylar-foil looking type and the one you want, the clearer diamond-cagey looking bag. Guaranteed? No. Better than nothing, Yes. Recycled, reusable, and the excitement of free!

 

[John Hayward]

Hi All,

I think everybody is pretty attuned to LED runnig and anchor lights and even LED flashlights. What I did in addition to all of the above is I got some LED Puck Lights for backup cabin lighting when I only want a little light or if the main electrical system suffers a complete catastrophic failure. Costco had them for $12 for 3 and West Marine sells them for $10 each (their typical profit margin). They run on 3 triple A cells which I will have about 4000 of. I have also converted all of the cabin interior lights to LED (red/white) but they do run off the main electrical system. Finally, I have a gimbaled Weems and Plath kerosene lantern.

As for lightening, I will do what I do at home and camping. If there is a storm nearby I will disconnect the radios completely and hope for the best. I speculate that if you are hit directly, fire and sinking will be your primary concerns and then survival whether in the raft or boat. I do carry and sorta know how to use a sextant and have several mechanical watches, so should be able to tell where I am roughly should all the GPS's, digital watches and the Loran fail. Two of the watches have built in Flux Gate compasses. Hitting the islands with no compass and no means to find even rough position would be problematic. Were I in this position, I would surely head back for the West Coast. It would be hard to miss that and it would be easy to find out where on the West Coast you were once you got there.

If you have an emergency, you are always better off if you have thought it through and have a plan. This gets you started and gives you breathing room. You can then reassess the plan and see if, under the circumstances, you can come up with a better one. Most of this sort of planning ahead for emergencies comes from flying. If you have an emergency in the air at several hundred miles an hour, you don't have time to ponder the possibilities, read up, call for advice, etc. you better know what you are going to do ahead of time.

Anybody out there ever been hit by lightening in a boat or know anybody that has? If yes, did handhelds, GPS's, digital compasses etc fail? If yes to the above, did anybody have handhelds in ovens or antistatic bags that survived when all else failed? I have never heard of read about anyone losing all their handheld electronics in a small boat due to lightening at sea, but I'm sure it must have happened at least once in history.

Remeber Joshua Slocum went around the world singlehanded with a sextant and a clock with only an hour hand............

John H
Dream Chaser

 

[brianb]

Faraday cage ? Use aluminum foil.

Just wrap it in foil and be done with it. That is a great faraday cage. You could do slightly better with silver foil .

Brian

You guys have probably already discussed this, but I just can't find where so I'll throw this in for redundancy. Faraday cages are shaped like that diamond plate screen thing that hangs in your paint bucket to roll off the excess paint. Your best/cheapest protection available against lightning are the anti-static-faraday bags we use to ship motherboards and hard drives. If you go into any local computer shop that builds computers, they've got these laying all over the place and you should be able to pick up 3-5 at $2-3 ea(max) if not FREE. Double bagging a spare GPS in these before putting into a waterproof, all vinyl, no metal bag, while not clipping it to anything metal on the boat is your safest protection against lightning, static, RFI signals, or EMP. Remember there are 2 kinds of anti-static bags. The mirror-mylar-foil looking type and the one you want, the clearer diamond-cagey looking bag. Guaranteed? No. Better than nothing, Yes. Recycled, reusable, and the excitement of free!

 

[nereida]

Lightning strike....

Hi All,


Anybody out there ever been hit by lightning in a boat or know anybody that has? If yes, did handhelds, GPS's, digital compasses etc fail? If yes to the above, did anybody have handhelds in ovens or antistatic bags that survived when all else failed? I have never heard of read about anyone losing all their handheld electronics in a small boat due to lightening at sea, but I'm sure it must have happened at least once in history.

John H
Dream Chaser

Hi John - Yes - "Nereida" was hit by lightning crossing the Bay of
Biscay to NW Spain - VHF aerial at top of mast was 'frizzled', all instruments toasted - including handheld GPS (off) in grab bag - 'dead as a Dodo'! Half an hour spent checking boat out, getting out & deploying emergency VHF antenna in case radio was working, allowing for drift and large 'circle of error', then had ship's compass and plotted position from 20mins prior to strike on paper chart to use to head SW hoping to keep clear of all dangers in deep water as headed on with very basic navigation!! Interestingly, depth readout was still there & seemed to be vaguely of the right order, according to paper chart, although temp readout on same instrument was showing stupidly high. Never could see any evidence of where lightning exited....
Eventually had Spanish fishing boat confirm position in daytime so we didn't miss coming inshore to get to La Coruna & head on unwittingly around Cape Finisterre instead! I expected handheld GPS to be OK but most definitely was not - circuit board was burned out! Ever since, handheld GPS and a computer is wrapped in Al foil & put inside (metal-lined) oven as a 'double Faraday cage' if lightning is around.... I know people who think that carrying 2-3 PCs and no paper charts is OK.... go figure!

Cheers,
Jeanne
"Nereida"
Trinidad (leaving for Panama Monday... keep your fingers crossed for my transit being timely...)

www.svnereida.com

 

[John Hayward]

Hi Jeanne,

Good luck on a speedy transit through the canal! Rumor has it they have reduced the number of small boats they let in at one time and it's clogging things up a bit. Hope it's not true.

Thanks for the story! Great testament to paper charts and farraday cages. Well we hope the farraday cages would do for lightening protection for PC, handhelf GPS and VHF. Did your primary VHF survive or did you just yell back and forth to the fishing boat?
Also, were any of your compasses adversely affected. I wouldn't be at all surprised to hear that the magnetic field of the boat was changed rendering the compasses simewhere between suspicious and worthless.

Thanks Again,
John
Dream Chaser

 

[nereida]

Lightning strike (part2)

... OK.. my 4th attempt - can I throw my computer out of the hatchway once I've finally posted this reply...???!!! Why does dragging my finger over the touchpad cause oblivion???? I digress.....

Hi, John!

I don't think rigging the emergency aerial achieved anything (later found the frizzled remnant of the aerial at top of mast - I still have the memento onboard!) -radio was replaced along with all instruments and radar (insurance covered it!). Certainly, the only two boats seen either couldn't hear or had their radios switched off - a French guy waved cheerily as he went on his way and a Spanish fishing boat was attracted by 'SOS' signals on foghorn and by torch/flashlight. Impressive the way their only 'English-speaking' crew member (think his English was only minimally better than my 3-4 words of Spanish!) jumped on to "Nereida" without any damage to her, despite their flared topsides and the big swell running at the time! I can't actualy remember if handheld VHF was used or not, but I'm sure that got replaced also.
Main compass seemed fine - I've no recollection of ever hearing of anyone whose main compass went down in a strike - I'd be interested to hear if anyone has heard differently. Didn't have an electronic fluxgate handheld at the time (I'd expect that to go down if not wrapped in metal foil) and didn't bother even looking at other 'basic' handheld (since main compass was fine) - but that's clearly OK now so must not have been affected then. Of course, when storm passes, you might have the moon or odd star out to keep steering your course by....
I would have expected that since the ionizing influence of the lightning around is a temporary phenomenon, the constant Earth's magnetic field would probably keep (electrically isolated) magnetic compass needles unchanged - any physicists out there who'd like to argue the point?? (I'll be off the Internet whilst on passage this week but would be interested..)
Can I start a new thread on a totally different topic - I've just spotted a gecko on board - anyone know how to catch or get rid of one without killing it??

Cheers,
Jeanne
"Nereida"

 

[Eyrie]

Posted on the 08SHTP web site is an excel worksheet to assist in calculating a boats energy consumption and recharging capabilities during the course of the race.
http://www.sfbaysss.org/TransPac/transpac2008/documents/electrical_budget_worksheet.xls
The worksheet originated from the Pacific Cup web site, has been in use for several years, and assumed to be correct, but after closer examination by Bob/Ragtime! and Rob/Tigerbeetle it seems the results of the worksheet can be misleading.

Below are the observations made by Rob/Tigerbeetle regarding the worksheet. Unfortunately this forum does not allow excel attachments, so to follow along with Rob's explanation you will need to go to the list of posted energy budgets that are on the web site and bring them up.
http://www.sfbaysss.org/TransPac/transpac2008/electrical_budgets/electrical_budgets.html

The calculation for charging time is flawed as it does not take into account the ability (or lack thereof) of the battery bank to accept a charge.

For example, if I look at Ragtime!'s budget I see that a 30 amp alternator will charge the battery bank in 90 minutes. If I change the alternator to be a 1000 amp output I am informed the charge is accomplished in 3 minutes. However, the batteries will not accept a charge at that rate and will in fact overheat and crack, explode, or catch fire (or do all three more or simultaneously).

The flaw is that the spreadsheet does not consider the maximum charge rate that a battery can accept; as a rule of thumb a lead/acid wet battery can accept a *maximum* of 25% of capacity when battery charge is below 85% of capacity.

To follow up further, the spreadsheet calculations are misleading, and decidedly incorrect.

For example, Alchera's worksheet calculates that he can cycle the batteries through a 50% charge/discharge cycle (the last 15% will be very slow and inefficient), and can push 90 amps into a 270 amp battery wet cell lead/acid wetcell battery bank - which isn't possible.

At best a 270 AH bank can accept 270/4 = 67.5 amp charge current between 50% and 85% charge, and then the curve changes dramatically.

The correct calculation is to a) ask the user which battery type they are using, and if the answer is lead/acid wetcell, the spreadsheet should fix the charge/discharge at 50%-85% and size the battery bank accordingly. For Alchera, this turns into: 270AH/day * 0.5 day between charging = 135AH to charge every 12 hours. To do this efficiently requires that the 135AH be no less than 35% of battery bank, therefore bank should be (minimum) 135/0.35=386 AH capacity (not 270).

That 386AH bank should be charged with an alternator no larger than 25% of capacity: 386/4 = 97AH alternator capacity (not 90).

That 97AH alternator will take 99 minutes to push 135 amps back into the bank at a charge acceptance efficiency of 85% (not 106 minutes).

None of the above numbers appear on Alchera's spreadsheet.

The upshot is the value of the spreadsheet is to get people to at least think about the power consumption they may have on board; the spreadsheet in fact produces incorrect data on how to size the bank and charger to determine charge times, and therefore may
lead people to believe they have a suitable system with sufficient fuel reserves to complete the race, when in fact they do not.

As a race entrant it is your responsibility to determine that you can power your boat during the course of the race, the worksheet is just an aid. If you have any doubt about your energy budget or recharging system you might consider seeking some advice from a knowledgeable source. Or perhaps someone in the forum audience will redesign a better worksheet.

Synthia/Eyrie

 

[AlanH]

So, making this up close and personal for Yours Truly....I have two, 90 amp-hour lead-acid batteries. My solar charge controller allocates 50% of the current from the panels to both batteries if they're equally discharged, or favors the more deeply discharged battery if they're not equal. Let's take the theoretically possible case of battery #1 being topped up and battery #2 being pretty drained. The 25% charging capacity that Rob mentions would mean that battery #2 can accept a maximum charge rate of 22.5 amps. That will taper off a LOT as the battery nears fully-charged.

I have 140 watts of solar panel capacity on the boat. It's reasonable to assume that about 110 of those watts will be generating at any given time since at least one panel will be at least partially shaded. So my array will generate about 6-7 amps in full sun. .....and that's well under any charge rate that will toast batteries, though the batteries probably won't accept 6-7 amps when they get over 90% charged..

6 amps multiplied by 8 hours a day is 48 amp-hours. 7 amps multiplied by 8 hours of day of full sunshine is 54 amp hours. I'll be somewhere in between. About 85% of that will actually get into the battery every day, meaning something on the order of 40 amps/day will get shoved back into my batteries from the solar panels, as long as there's sun. That, right there is enough to replace the autopilot drain and the lights.

If I can manage to get all 140 watts of solar cranking for 8 hours, that adds up to about 56 amps a day going into the batteries, which will cover everything.

In addition to this I'm carrying an old 1990's' vintage Coleman "lightning" generator which according to the label shoves out 50 amps and has a charge regulator. I have my doubts about that amperage rating, but whatever the case, an hour with that thing shoving out electrons will give any battery a big boost, around 40 amps back into a well-drained battery.

 

[tiger beetle]

I have 140 watts of solar panel capacity on the boat. It's reasonable to assume that about 110 of those watts will be generating at any given time since at least one panel will be at least partially shaded.

If the solar panels are a typical parallel/series cell wiring, shading a cell will result in the panel output dropping by half. If you have 2x70 watt panels, shading one panel reduces output of the panel pair (under perfect test conditions) to 105 watts.

As regards solar panel efficiency, it's been suggested by several panel testers that a realistic output seen on a boat for a given panel is: (rated watts - 10%) / 2 = (140-14)/2 = 63 watts. Given that watts = volts x amps, you need to know the voltage *at the battery terminal* (not the panel) in addition to the panel watt output to calculate amperage available to recharge the batteries.

To know how well your boat's charge system works will require that you be a bit more precise in your expectations. A 'well-drained battery' should be defined in terms of voltage, and then the time to recharge to a higher voltage at a specific current can be measured.

The Coleman (originally Active Technologies' Lightning Charger) gas-engine battery chargers were good units, I had one which worked well until the ceramic in the alternator winding cracked - unfortunately Coleman Powermate stopped making the unit. The problem with the little Honda generators is they are battery replacements and do not have high enough voltage to act as battery chargers. The Coleman unit really does have output voltage that will charge a battery.

Trying to do someting as simple as charge a battery is really rather interesting.

- rob

 

[AlanH]

If the solar panels are a typical parallel/series cell wiring, shading a cell will result in the panel output dropping by half. If you have 2x70 watt panels, shading one panel reduces output of the panel pair (under perfect test conditions) to 105 watts.

As regards solar panel efficiency, it's been suggested by several panel testers that a realistic output seen on a boat for a given panel is: (rated watts - 10%) / 2 = (140-14)/2 = 63 watts. Given that watts = volts x amps, you need to know the voltage *at the battery terminal* (not the panel) in addition to the panel watt output to calculate amperage available to recharge the batteries.

To know how well your boat's charge system works will require that you be a bit more precise in your expectations. A 'well-drained battery' should be defined in terms of voltage, and then the time to recharge to a higher voltage at a specific current can be measured.

The Coleman (originally Active Technologies' Lightning Charger) gas-engine battery chargers were good units, I had one which worked well until the ceramic in the alternator winding cracked - unfortunately Coleman Powermate stopped making the unit. The problem with the little Honda generators is they are battery replacements and do not have high enough voltage to act as battery chargers. The Coleman unit really does have output voltage that will charge a battery.

Trying to do someting as simple as charge a battery is really rather interesting.

- rob

Rob, my panels all feed into one common bus bar. All the positive leads go together, all the negative leads all lead together. Voltage in full sun at about 4:30 with the panels all pointing straight up, on Sunday at Coyote Point was 19.08 volts at the bus bar. One single lead goes from the bar to the Morningstar two-bank charge regulator.

See, one 30 watt panel is across the top of the companionway and whenever the boom is near the centerline, it will be shaded. The two 40 watt panels are way out on the stern pulpit, so usually in full sun. The other 30 watt panel is mounted on a gizmo that stuffs into the winch handle holes on a winch, so it moves around and I can keep it out of the shade.. OK, so if the 30 that's on the cabintop is shaded, it's output is halved. That would leave me with 40 watts + 40 watts + 30 watts + 15 watts = 125 watts. 125 watts div by 17 volts (Kyocera's short-circuit voltage, I'll assume it's the same for the other panels) = 7.35 amps.

7.35 amps generated over 8 hours of sunlight = 59 amps in a day. Wooo-hooo!

Let's do some more....

You wrote that I need to know the panel voltage at the terminal. By that I assume you mean the battery terminals. The Morningstar charge regulator I'm using has dip-switch settings for Lead Acid and sealed batteries. If I remember rightly, the Lead Acid charge setting is 14.4 volts and the sealed battery charge setting is 14.1 volts, though I might have those backwards. Let's say it's 14.4 volts. Now, the rating for the panel array is to take the wattage of the whole shebang, subtract ten percent and divide by two. OK for my 140 watt array, that gives 63 watts, like you said. 63 watts div by 14.4 volts gives 4.3 amps. Eh? Ouch! That's' only 35 amps a day, for an 8-hour day of sunlight. If that's how it works out I'd better take 4-5 gallons of pre-mix for that Lightning generator and use the Navik windvane a lot!

Did I get that right? The shaded panel (unless it's *really* shaded) drops IT'S contribution in half, it doesn't drop the WHOLE ARRAYS output in half?

The Coleman Lightning generator is a champ. I'm almost tempted to ship it back from Hawaii, but it being a gas engine and all.....probably not practical.

 

[tiger beetle]

Rob, my panels all feed into one common bus bar. All the positive leads go together, all the negative leads all lead together. Voltage in full sun at about 4:30 with the panels all pointing straight up, on Sunday at Coyote Point was 19.08 volts at the bus bar. One single lead goes from the bar to the Morningstar two-bank charge regulator.

That's good voltage and seems excess to requirements. A top-end charge voltage should be 14.6 volts, almost never as high as 15 volts. Many panels will show a no-load voltage of 17 volts, and 19 is way up there. Now measure the voltage at the battery terminal - that's the voltage the charger can deliver to the battery. This takes into account loss through the wiring, the charge controller, and a blocking diode (if you installed one).

So, knowing that much, would shading of one panel seriously drop the output of the array as a whole? It sounds like you're suggesting that it will.

Yes, if the panel is a typically-wired panel. Each solar cell delivers a small portion of the total voltage, and the cells are wired in series/parallel to deliver the design voltage x amps to the panel output terminal. Shading a cell kills the section of cells that the shaded cell is part of. This is easy to test - place a small piece of wood on the panel such that it covers part of one cell, and see what the effect is. Continue with shading more and more cells to determine when the panel output drops below a charging voltage of perhaps 13.6 volts *at the battery terminal*.

EDIT: the shaded cell only affects output of the shaded panel; a shaded cell of panel A does not affect output of Panel B. The output of the array as a whole will drop, but not necessarily by 50%.

See, one panel is across the top of the companionway and whenever the boom is near the centerline, it will be shaded. If shading that one panel (the most likely one to get shaded) will kill the output of the whole danged thing, I'm inclined to put a little switch on the + lead of that panel.

That's a good idea, but most likely unecessary. In practice the shadows will be swinging all over the place, periodically shading different parts of different panels. The loss caused by a shaded panel as it draws from the unshaded panel is minimal in an environment in which the shading is partial and inconsistent.

The Coleman Lightning generator is a champ. I'm almost tempted to ship it back from Hawaii, but it being a gas engine and all.....probably not practical.

If you want to sell the generator after the race, let me know.

- rob

 

[AlanH]

What may be more helpful is to ask them what they will do if the on-board electrical system suffers catastrophic failure halfway there - then what??? They lose charging ability, storage capacity, or suffer an electrical fire.... A lightning strike, anyone???

Do they have a plan for that???? How exactly do they get the boat across a thousand miles of ocean and find a safe harbour - at that point, probably not even Hanalei Bay??

In the case of total electrical charging system failure; solar panels disabled, Coleman charger won't start:

1. all my GPS's are AA battery-powered and I'll have a LOT of spare batteries. With those, parallel rulers, a pencil, paper charts and four pairs of reading glasses (I can't read diddly without glasses any more) I ought to be able to find Hawaii. My oldest GPS lives in a Faraday cage, a little aluminum box I made out of roof flashing so that it has at least a snowballs chance in hell of surviving an electrical strike. And finally, I have three watches on the boat and a sextant and tables. God Forbid..

2. the running lights are a tiny little draw now that I've put on LED bulbs, so the batteries will keep them running for quite a while. i also will have several big 6 volt lantern batteries on the boat and the boats strobe lights work with those quite happily. They just don't flash quite as often. I also have three armband strobes that work on D-cell batteries for about 3 nights....and I have a lot of extra D-cell batteries. So I'm lit up at night.

3. the Navik Windvane will do a LOT of steering, which it's entirely capable of doing.

4. I'm renting a satellite phone and an extra battery. I won't be chatty, but people will know where I am, once a day.

How 'zat?

 

[AlanH]

Shading a cell kills the section of cells that the shaded cell is part of. This is easy to test - place a small piece of wood on the panel such that it covers part of one cell, and see what the effect is. Continue with shading more and more cells to determine when the panel output drops below a charging voltage of perhaps 13.6 volts *at the battery terminal*.

EDIT: the shaded cell only affects output of the shaded panel; a shaded cell of panel A does not affect output of Panel B. The output of the array as a whole will drop, but not necessarily by 50%.

If you want to sell the generator after the race, let me know.

- rob

That's a really good idea, and simple to do. OK, quick project for Sunday!

I would very much like to sell the generator to someone who will use it, I'll get back to you.

 

[Libations Too]

....As regards solar panel efficiency, it's been suggested by several panel testers that a realistic output seen on a boat for a given panel is: (rated watts - 10%) / 2....
- rob

Rob,

I always appreciate your perspective...but why does the formula above use a factor of 50% (divide by 2) to get to actual watts? I can understand the 10% factor as line and other losses, but a 50% reduction to rated output seems extreme. What am I missing here?

 

[tiger beetle]

Rob,

I always appreciate your perspective...but why does the formula above use a factor of 50% (divide by 2) to get to actual watts? I can understand the 10% factor as line and other losses, but a 50% reduction to rated output seems extreme. What am I missing here?

All I know is I read 3 different published reports derived that equation empirically. Based on observations of my Kyocera 120 watt polycrystalline panel, I'd say that's about right for my installation.

Manufacturer's rating tests are designed to make the panels perform their absolute best - the panel is temperature controlled, perfectly clean, the wiring to the panel junction box is brand new, and the light is unobstructed and at the best possible angle and wavelength.

What I find is that my panel usually has dust on it, the sun is other than directly overhead most of the time, the panel heats up in the sun (increasing resistance and reducing output), the panel is partially shaded at times, and I'm measuring output at the battery terminal where the panel can do useful work as opposed to the manufacturer whom measures output at the panel's junction box.

If you have a panel it's relatively easy to measure how it behaves in real life, which is always better than an empirical equation or rule of thumb. Until you buy one you're limited to calculations to forecast the work the panel will do. My goal was to have the panel supply the power the onboard refrigeration consumes (which it does). Ultimately I simply purchased the panel with the highest watt/square inch energy density that fit within the footprint I had available. Turns out the panel kept up with not only the fridge but also with the limited (3 hours/day) laptop power use - which was an extra bonus!

- rob

 

[BobJ]

I have two Kyocera KC-40T (43 watt) panels (20"x25"), each with a rated output of 2.48A, so a total of 4.96A. They are connected to the batteries via a Flex Charge PV7-D dual-bank controller.

My real-world observation, via my battery monitor, is that the batteries are receiving 4.8A from them if I make any attempt to aim them towards the Sun.

Sometimes a shadow of the upper lifeline cuts across one or both but because it's a thin shadow, it doesn't seem to affect the output much. I can pivot them fore 'n aft, from near vertical (if the Sun is in front of the boat) to flat against the transom (if the Sun is behind the boat).