[modeleng] Re: Battery problems

Alan Stepney wrote:
> OK, for todays silly suggestion, check the charger.
>
> There is a possibility that the rectifier has gone short circuit, and 
> putting, say, 20+ volts AC into the battery wont make it very happy.
>
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>   
As an electronics engineer, I tend to agree, with some of you, who 
state,that the battery has been producing an excess of H2 and some other 
gases, that come with charging a battery of this kind.
It is unlikely, that the vent would not become "unblocked" when gas is 
produced.(and these batteries have an added "safety valve")
What is likely in my opinion, is that the load current was rather high, 
and that the amount of gas produced was higher then acceptable.
On top of this, you are dealing with volatile gases that are heated up! 
this occurs because of the loading.
All this together, is still an unlikely scenario, though.

I suspect, that because of the frequent moving in and out of the battery 
(out and in the car) that some plate(s) lost part of their (lead) charge 
and shorted.
If you add that to the above, you might get a result as shown in the 
pictures.
On the other hand, most deep-cycle batteries, (I have worked with this 
type more then the others, but they are basically the same) I have seen 
in this state, were simply connected wrongly to the charge current....
And that, will kill a battery every time....

Also, there is something to be said, in connecting batteries in series, 
only if they are of the same brand and type. Every manufacture makes his 
batteries according to his specifications, and the "internal resistance" 
will differ, with the brand and type.
A difference in "internal resistance" will eventually cause degradation 
of the plates (and loose bits!) and internal short circuits. (one 
battery is using current from the other, as it passes trough the plates, 
as it were..)The internal resistance starts to differ more and more as 
the battery heats up, and the problem gets worse...
So beware! If it is really needed to switch two batteries in series (Pb 
batteries) make sure that they are both new, and of the same make and 
time. Try and charge them when switched in series, with a 24 V charge.
If the choice is there, a long and slow charge is always far better then 
a slow "burst" charge (or whatever they call it these days!)
If possible use "deep-cycle" batteries (the type used in caravans and 
the like) These are designed for erratic discharge and will last longer 
for the kind of application suggested in this case.
As a new battery needs to be bought for this application anyway, you 
might consider a 24V one and be done with all the possible trouble 
mentioned above...


Cheers
Patrick
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