"....Resistor burns out over time and over charges the batteries..."

 

If we are referring to a current limiting resistor (which is their primary job anyway), when they burn out they go high value which means that they are effectively open circuit thus preventing the battery from recieving it's charge...a common fault when batteries are not replaced. In these circumstances the battery cannot be over charged, in fact it cannot be charged at all... perhaps I am not referring to the resistor in mind.

 

"....thinking that the loose core might be the problem...."

 

There are many circumstances where loose cores  are deliberately left unconnected.... When using a six core cable to connect a four wire door sensor trade installers tend to leave the remaining two cores unused but available for further use if needed although it is better to terminate them beneath a spare terminal without stripping the cores...A five terminal sab would see a spare core, although it is usually doubled up at hold of positive.. Best plan, if you see a loose core leave it alone unless you know for certain where it goes.

Usually find the charger voltage is 15v+ when the resistor goes pop

Hi, If it is +15v, that means that the battery is being overcharged, though, right?

 

I thought on the basis of faults that the spare core might have become unterminated.

The charger might be at fifteen volts..although that sounds a bit high to me, but in my experience when the CLR to the battery has gone high value then it prevents any voltage getting to the battery..high value resistor..resistor burnout..means open circuit to the battery (common sense really). Worth putting your meter on the ends of the battery leads though to confirm one way or the other (let me know), but that fifteen volts bothers me considering that the nominal voltage is around 13.6 to 13.8 at the power supply. The other point regarding the battery being overcharged is also puzzling, in a sense, since the psu regulates (or trickles) the charge according to battery condition (the internal cells of the battery represent a resistance also). Without any further evidence I would conclude that the psu is or was trying too hard because of the condition of a battery (Although we must take into account the times when a full recharge is occuring).

Edited August 6, 201510 yr by charlie6

Normally see it on panels that haven't had the baytery changed regularly. IIRC

last one was 15volts and a battery fitted about 9 years prior.

Showed as flat battery on act tester tho.

Fair comment, I think nine years is pushing his luck a bit though.