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Old 24-05-2012, 03:14   #1
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Dead Batteries -- Blast Them or Coddle Them?

Got back to the boat last night after three weeks to find every battery (3 banks) dead as a doornail. D**n! My house bank now consists of $2000 worth of brand new Trojans -- double d**n!

It turns out that I left my compass light on, and although the last three weeks have been windy and stormy, the bloody Rutland wind generator couldn't even keep up with that tiny load! Bloody useless thing -- so much money and trouble, and all for nothing, it seems.

So i had a lot of fun last night, in the dark, on my mooring, trying to get some diesel engine started so I could bring the electrical system back to life. The only battery with a good charge was the tiny Varta start battery for the dinghy outboard(!). Getting that out was quite a trick -- with no power, I couldn't operate the electric davits or even open my hydraulic transom platform to get at the dinghy to get the battery out. I guess all you "back to basics", "simpler is better" folks will be laughing your a***s off at this point. After great acrobatics -- in the dark -- I finally managed it.

The generator would fire up, but would not keep running -- it has an electric lift pump which I guess just doesn't pump enough if there are not at least 13 volts in the system. Finally, by jumping together the dinghy battery and the genset start battery, I got the main engine started -- bless you, Yanmar! That engine, a 4JH3HTE, is the best starting diesel I have ever been around. If you can get the crankshaft to turn over even half a revolution, it fires up.

So now I have to get juice back into all those batts, and I hope that the Trojans are more resistant to this treatment than the Vartas I killed last year. What's the best way to do it? Bring them back up slowly, using the genset and regular battery charger? Or run the main engine and let the 110 amp (x 24v) schoolbus alternator blast them? Or run both the main engine and genset at the same time? I don'tunderstand the chemistry involved, and last year I failed to revive my previous set of batteries. All advice gratefully received.
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Old 24-05-2012, 03:24   #2
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Re: Dead Batteries -- Blast Them or Coddle Them?

Dockhead, your compas light couldn't have flattened 3 house banks worth of batteries in 3 weeks surely? That electrical power is going somewhere else, perhaps the fridge etc.

Would love to have seen the acrobatics last night, we need a webcam on the river Would have lent you the Honda 20i but we sold it last week as it wasnt' being used and solar will meet our needs.

As for the batteries, I would be tempted to charge via the genny and normal charger slowly if they are new.

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Old 24-05-2012, 03:42   #3
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Re: Dead Batteries -- Blast Them or Coddle Them?

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Dockhead, your compas light couldn't have flattened 3 house banks worth of batteries in 3 weeks surely? That electrical power is going somewhere else, perhaps the fridge etc.

Would love to have seen the acrobatics last night, we need a webcam on the river Would have lent you the Honda 20i but we sold it last week as it wasnt' being used and solar will meet our needs.

As for the batteries, I would be tempted to charge via the genny and normal charger slowly if they are new.

Pete
Well, half an amp for three weeks is 250 amp/hours, more or less. The fridge was not on. Maybe there is some other leakage.

I don't know why the engine start battery was flat. It is totally isolated from the house bank (they are not even the same voltage). Unlike the house bank, it was not dead, just flat with 12 volts or so, not enough to turn over the engine.

Your Honda would have come in extremely handy last night! It was really a PITA!

Yes, the house batteries were new -- they aren't now!! I guess I'll run the genset all day and see if they come back to life. If not, I guess I'm out another 1300 quid!
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Old 24-05-2012, 03:43   #4
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Re: Dead Batteries -- Blast Them or Coddle Them?

Gotta agree with Pete7. Something else is going on, a compass light combined with a wind generator shouldn't drain a house bank.
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Old 24-05-2012, 03:45   #5
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Re: Dead Batteries -- Blast Them or Coddle Them?

How many amps do you have in 2K worth of Trojans?
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Old 24-05-2012, 04:04   #6
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Re: Dead Batteries -- Blast Them or Coddle Them?

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How many amps do you have in 2K worth of Trojans?
420 amp/hours at 24 volts.

I'm going to check the voltage drain with my DC clamp meter before I leave the boat the next time.
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Old 24-05-2012, 04:15   #7
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Re: Dead Batteries -- Blast Them or Coddle Them?

Whilst I really do suspect something else is powered up even when its all switched off, however, there is a chance that you have one duff cell in one of the Trojans. Since they will be gassing nicely by now it would be worth checking the cells for bubbles to rule this out.

How is the inverter isolated when you leave? that would do it as would the genny if the volts could flow back through the coils when its stopped running.


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Old 24-05-2012, 04:33   #8
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Re: Dead Batteries -- Blast Them or Coddle Them?

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Whilst I really do suspect something else is powered up even when its all switched off, however, there is a chance that you have one duff cell in one of the Trojans. Since they will be gassing nicely by now it would be worth checking the cells for bubbles to rule this out.

How is the inverter isolated when you leave? that would do it as would the genny if the volts could flow back through the coils when its stopped running.


Pete
The inverter is part of the Victron integrated inverter/charger. I leave the Victron switched off altogether, and the 230V system likewise completely shut down. I don't think that could be it, unless the Victron is malfunctioning somehow. I will start checking with the clamp meter when I get a chance to see how much power is going out, and where.
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Old 24-05-2012, 04:55   #9
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Re: Dead Batteries -- Blast Them or Coddle Them?

Man!!-what a bummer. You are going to get some sympathy on this one.
Maybe Victon charger side off--but inverter possibly loadseeking?
Stereo memory powered up?
Level seeking bilge pump switch maybe?
These little "helpers" can be a real PITA.
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Old 24-05-2012, 04:58   #10
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Re: Dead Batteries -- Blast Them or Coddle Them?

Sorry for your troubles, maybe a short in the system. Could be the wind generator is actually putting out more amps than suspected.
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Old 24-05-2012, 05:54   #11
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Re: Dead Batteries -- Blast Them or Coddle Them?

Thanks, guys, for the sympathy! Such a PITA. I get back to the idea that battery banks should have a safety switch or battery management system which totally isolates them at the battery posts when they get to a dangerous level of charge -- just like our laptops and cell phones do. Would save a lot of killed batteries.

Does anyone have any insight into the question about battery chemistry -- whether it is better to bring dead batteries back with slow charging or fast charging?

I charged for a couple of hours last night before turning in. Woke up and the batts were at something less than 24 volts, a near 0% charge according to the table I have.

Now I've charged them for 3 1/2 hours, two hours of which I was using the big alternator on the main engine. I shut down all charging half an hour ago, and now the batts are showing 25.6 volts That does not, of course, mean that they have been revived -- they were still accepting 20 amps when I shut down the genset -- but it doesn't suck, at least, so far. I'm going to let them rest for a few hours, then start charging them again with the genset. We shall see.

I have another question -- how do you guys monitor our battery charge state? I have a Victron battery monitor which counts amps in and out. Because of the way it is wired, I don't trust the amps-counting function and don't pay that much attention to it.

I have been watching the voltage. It's not practical for me to do a textbook open circuit voltage test -- totally isolating the batteries for several hours. So what I do is check the voltage when there is only a small load on -- no more than 4 or 5 amps -- and when there hasn't been either any charging or any heavy loads for a while. My logic is that 4 or 5 amps on a 420amp/hour battery bank should not be enough to pull down the voltage too much below what the true open circuit voltage would be. Do you electrical wizards agree with this approach? What do you guys do? I follow a table I have from somewhere, and consider that:

25.2 volts (equivalent to 12.6 on a 12v system) is 100%
24.8 volts (equivalent to 12.4) is 75%
24.4 volts (equivalent to 12.2) is 50%
24 volts (equivalent to 12) is 25%
under 24 volts and you are screwed.

I will start charging latest when I see 24.4volts under a light load.

Does this make sense? What do you guys do?
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Old 24-05-2012, 10:46   #12
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Re: Dead Batteries -- Blast Them or Coddle Them?

Somewhere on another thread on CF, it was said that Trojan recommends a 12 volt battery be charged to 14.8v. to achieve full charge.
That would be 29.6volts for your setup.
Read this guy's charging story. It's "illuminating".

https://handybobsolar.wordpress.com/...d-up-so-angry/
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Old 24-05-2012, 11:06   #13
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Re: Dead Batteries -- Blast Them or Coddle Them?

yer loosin amps somewhere....
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Old 24-05-2012, 11:08   #14
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Re: Dead Batteries -- Blast Them or Coddle Them?

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Somewhere on another thread on CF, it was said that Trojan recommends a 12 volt battery be charged to 14.8v. to achieve full charge.
That would be 29.6volts for your setup.
I think that's AT 14.8 volts, not TO 14.8 volts. I'm not talking about the charging voltage; I'm talking about the batteries open circuit voltage (or pseudo open circuit voltage) as a measure of the state of charge.
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Old 24-05-2012, 11:13   #15
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Re: Dead Batteries -- Blast Them or Coddle Them?

A 100% charge will be 12.6 volts after battery has had 24 hours of rest with no load.
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