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nvydvrdude · 10-10-2017, 11:52 AM

Went to a Forest River Rally in Goshen the first week of August. It was fun, and I sat through some classes, learned a few things. One class was done by the electrical guy for the 5th wheel division. He said something that I don't really understand, "todays modern converters could boil off 6v batteries if the voltage of the batteries dropped to low". Any body know anything about this? I would like to put in some 6v's but, not sure about the boil off thing. Unfortunately I didn't get a chance to talk to him about it.
Thanks

nothermark · 10-10-2017, 12:07 PM

Off hand I would guess that he expects multi stage converter chargers will reduce the output voltage if the batteries are too low. That will let them keep pumping current into the battery with reduced electrolyte so there is more chance of boiling off more. The older converters don't adjust but do collapse the output voltage to protect themselves. You won't charge the batteries that way if they are below some threshold like 10 V.

NRR · 10-10-2017, 06:12 PM

Humm… I have had three stage chargers on two 6V batteries since 2006 and never had them boil off. I inspect them and if low in fluid I add distilled water.

Maybe it is a fiver thing!

twinboat · 10-10-2017, 07:05 PM

The only time you could boil the batteries is if you have a higher output charger then recommended for the AH capacity of the batteries.

With 200 AH of flooded battery, the charger recomendation would be around 15 % of that or 30 amps.
It would put out 30 amps from very low state of charge to about 70% SOC before the voltage increased enough to cut back the amps. That would be OK.

If you were using a 60 amp charger on the same low batteries, you would be overcharging and boiling them, up to about 70% SOC.

If you run your batteries down to only 50 to 60% SOC, you could get away with a 60 amp charger. The battery would probable reach the 70% SOC and cut back before they boiled.

Gary RVRoamer · 10-13-2017, 12:33 PM

Mostly technobabble. Modern chargers won't boil any battery that is in decent condition, whether 2x 6v or 12v's.

However, if a battery begins to go bad, e.g. either high or low internal resistance, the charger tries harder and harder to get it charged and that can begin to boil it. And any other battery connected to it, since they charge as a set. Nothing unique about a 6v in that regard, though.