24v solar system question - from Greece!

Re: 24v solar system question - from Greece!

You've got perhaps two problems:

29.6 is not high enough for an equalization charge, but you shouldn't need to be doing this yet (Trojan recommends checking specific gravity for too much variation before doing an EQ charge). If that's all it will allow, the charge controller should be changed. That is in fact just about what a 24 Volt system with Trojan batteries will Absorb at.

Load consumption looks like;
Inverter 360 Watt hours, caravan power (probably does not draw 20 Watts all the time) 480 Watt hours, LED's 11 Watt hours, TV 40 Watt hours. At that point you're up to 890 to 900 Watt hours. This should not be severely affecting the state of charge of the batteries as it is less than 25%.

That means either the loads are much higher than you expect or the batteries are not getting charged fully. You are right that Voltage alone is not a good indicator of state of charge: it really only works with batteries at rest (no current in or out for a couple of hours minimum) which is not practical on a working system.

Adding more batteries is probably not the solution here, because if the ones you have aren't getting properly charged more will just be worse. As before, get a hydrometer and check the SG of the cells. If the charge controller has adjustments for Float level, turn it up to 27.6 if possible.

Also, does this charge controller have a remote temperature sensor? If not it would be a very good idea to get one. I suspect the controller is the culprit here, with its lack of flexibility to accommodate the Trojan's Voltage levels.

Re: 24v solar system question - from Greece!

yiannis5 wrote: »

Thanks again!

1. Yes, the charge controller has a temperature sensor - is there specific temperatures I should be looking when charging? According to the solar chargers specs the battery parameters at temperature of 25 Celsius are

What the temp sensor does is adjust the charging Voltage (usually the reading, not the set points) to compensate for temperature differences above/below 25C. When the battery is hotter it needs less Voltage to achieve full charge, when colder it needs more.

Float voltage = 27.6
Boost voltage = 29.2
Equalization voltage = 29.6
Equalization duration = 2 hours

Above figures cannot be altered...

That is a problem. "Boost" Voltage is being used for what we'd normally call Absorb Voltage. The base line for this on a 24 Volt system is 28.8. An EQ Voltage that is only 0.4 Volts higher than Absorb is useless. Likewise you want to be able to control the length of time for both Absorb and EQ. It almost sounds like this unit does not EQ, but instead they have used the term in place of Absorb. However, the lack of adjustable settings is a problem no matter what you call them.

Maybe the solution here is after I get accurate readings through a hydrometer to perform an equalization through my Inverter / Charger since it is totally configurable? Also just a thought but I read somewhere that new batteries take up to 100 discharges / charges until they reach full capacity?

This is a very good idea. There is nothing that can take the place of correct SG readings for judging a battery's state of charge.

Also what is the correct overnight voltage for my batteries taking into account my daily loads? Loads that are running overnight is the inverter / charger / caravan power and that is all!

Some general info about deep cycle batteries: http://www.solar-electric.com/deep-cycle-battery-faq.html
The Voltage is not going to be an accurate indicator of SOC on an active system. But the quick drop to 24.6 and overnight fall to 24.2 sounds like capacity has been compromised due to undercharging. When charging stops (no more Float) you can expect battery Voltage to drop right away, but it should be more like 25 or more Volts, not less. The overnight loss should also be minimal, unless the current consumption in that time is highest for the day.