Electro Beke

[CapnK]

Hands raised. Hooked up the gel's yesterday and been running fans and lights w/no noticeable drop in analogue voltmeter. Load tester due to arrive today, so we'll see which direction to go once that test is done...
Put a flooded G24 in the starter position for right now, WalMart Maxx brand (5 year warranted; 3 years free replacement, last 2 years pro-rated) for only $100. Will move it to skiff if replaced with a gel, pending gel house bank health.
If gels don't look good, checked around at local golf cart shops and found out that they are no longer using Trojans; production has moved offshore and quality has dropped. They are now using (IIRC) either US Battery or Interstate, spec'ed the same as Trojans, higher quality, and about $20 cheaper than a T-105.

[Bob J (ex-misfits)]

That's good to know about the T-105's.
No sooner had I posted about Mike & his 8 year old agm battery bank saw on another site they're beginning to fail. Hope I didn't jinx him :)

[CapnK]

Proooobbabbly gonna go buy those US Battery 1800's. The gel cell load test results were bad on one, and *excellent* - especially for a 12+ year old battery - on the other.
Odd, that, in that they have been hooked together in parallel for the past 9 years. I've always read that a bad battery will drag down a good one - but maybe that is not so true for gel cells...

That's good to know about the T-105's. ...snip... Hope I didn't jinx him :)

:o :-X hehe

[matt195583]

CapnK, my understanding of the bad battery dragging down a good battery is that the average voltage of the bank is what the charger/regulator will read. The charger will then over charge the good battery and under charge the dud. Under charging the dud wont do it any good or much harm but over charging the good battery will kill it pretty quick. The "dud" may still be serviceable on its own but coupled with a new battery it is a battery killer.

Regards Matt.

[CharlieJ]

My understanding also

[Norman]

An incomplete analysis of the "Good" battery, "Bad" battery question.

Let's take an example of two identical batteries, one in cranking service, the other in house service.  Each is connected to a battery selector with 1, 2, OFF, BOTH positions.  The cranking battery is connected directly to the high capacity alternator and starter solenoid.  The house battery connects to the breaker panel, and any shore power charger.  We will not consider shore power available.

First, lets presume the cranking battery is relatively inaccessible and you have beat to windward in rough conditions.  If some acid has splashed out on top, creating acid bridges, it slowly dischargs either cells or the whole battery.  You attempt to start, and the battery is not up to the task, so you select BOTH, and crank just fine.  Then, you leave the selector in BOTH to recharge both.  If we shut down the engine and leave the selector in BOTH, they will discharge through the acid together, and the "bad" battery will get the blame.  Replacing the "bad" battery will fix the problem, as the acid bridge will leave with it!  Simply cleaning it would have done the trick.

Second if the cranking battery develops a shorted cell, making it a 10 volt battery, cranking will be weak, and again, the switch is set to BOTH, and the engine is started.  Leaving it in BOTH to recharge both makes sense, but again, if left in BOTH after the engine is shut down, the 12 volt battery will "charge" the 10 volt battery, discharging itself.  The reality here is that after the "bad" battery reaches its charged state, it then gasses and converts water to oxygen and hydrogen.  This is the classic case of the bad discharging the good.  Charge voltages will not be correct, and if the engine is run for a long time, the good battery may be damaged.

Third, if the house battery is badly sulphated due to too many deep discharges, it will have very few "amp hours" left.  Let us make our imaginary cranking battery 100 AH in its present state, and the house 20 AH.  IF we deplete the house battery, then go to BOTH the cranking battery will not only feed the load connected, it will recharge the house battery until the voltages are equal.  This depletes the charge on the cranking battery by nearly 20 AH.  If we use 40 or so AH for house load, the cranking battery is now down to 40 AH, and if we try to crank with BOTH the 20 AH in the house battery will add to the 40 in the cranking battery, and help crank the engine.  If we select house load to house battery and crank, we have only 40 AH available, and cranking may be slow!

The preventive maintainance is to keep the batteries clean and properly watered, and occasional following a charging session, separate the batteries, and let them rest a couple of hours, then carefully measure the voltage.  If the voltage is exactly equal, no problem, they can remain in parallel.  Even if your batteries are normally in parallel, they should have a switch of some kind to separate them in emergencies or for maintainance and testing.  The ground common needs no switch.

Any boat with a house and a cranking battery should normally keep them separate, so they cannot both go down together for a single problem.

Obviously this is limited to flooded lead acid technology, but the issues are similar in other batteries.  Testing the unloaded open circuit voltage after a few hours for the chemical reactions to stabilize will tell you whether the two batteries can be trusted to live together.  A digital meter that reads to two decimal places should be used.  In this case, the actual accuracy is not important, as the issue is not the exact actual voltage, but the exact EQUALITY of the voltage.

I hope this helps make sense of the problems with batteries, good and bad, in a bank.

Norman

[CapnK]

I'll have to go back to Norm's I'm sure excellent and lengthy post :) but it makes sense in this case, Matt, as the 'charger' was a solar panel with regulator, so no extreme voltages were ever involved, at least not enough to damage the good battery while trying to 'make up for' the bad one like a 110v AC charger would do.

[CapnK]

A Grog for Norm, now that I have read. It was not that lengthy at all. :)

[Shawn67]

Truth is however at this moment in time I'm struggling with either an EP system or just saying the heck with ascetics & putting a 9.8 Tohatsu on the transom & calling it a day. These are after all sailboats :)

I just went though this on my Sabre 28. I decided on the Suzuki 9.9 BTX instead of the Tohatsu though. I have been thrilled with it so far. I can start a new thread if you want more details.

Shawn

[CharlieJ]

I have a Yamaha 8 hp 4 stroke- many many hours, and miles. Love it