Problem with charge control or battery

[trentman]

I have a 500 watt wind turbine 24 volt hugh piggott type

My system is 24 volts and 330 amp hour battery bank.

My batteries are 3 months old and read at the moment 25.6 volts

the specific gravity is 1.16 which i assume is only 25 percent charged

We have had wind for 2 days and my ammeter displayed between 10-20 amps

for most of the 2 days.

We only consume 40 amp hours per day.

Please advise if i have set my charge controller correct

I have it to come on at 28.4 volts and off at 26.5 volts

It dumps to two 8 amp loads one about 0.2 volts more than the other

Please advise why it is not keeping my batteries full

regards Mark

[Flux]

You either have more demand than you are producing or the controller needs setting higher.

This type of on off controller tends to let things get undercharged. 28.4v is just about enough to charge but it needs maintaining at this voltage for a fair time. If you are tripping off at this voltage then you will eventually become discharged. If you equalise regularly it may be just enough. The 26.5 is reasonable to come back on if you have load removing the surface charge but if there is no load then you are wasting a lot of your potential charging current.

As you have been able to measure the sg you must have flooded cells and you will do them less harm if you raise the voltage settings. I don't think it will hurt to raise the top point to 30v as far as the batteries are concerned, just keep an eye on the sg and make sure it comes up and stays up, if you use too much water and the sg stays up you can reduce volts a bit.

The immediate snag that I can see is that your inverter may trip on over volts so you may have to compromise.

If you can reduce the differential between the switch on and off points then you may be able to switch off at 29v and on again at 28.

If you have trouble with the inverter tripping then you may have to set your controller higher at times when you are not using the inverter to get the batteries back up, they need a good equalising at present on the first windy day, the first thing is to get them back up and then try raising the settings to keep them up. If that fails then you must be using more than you are producing. Output from wind generators is very variable so it is often difficult to judge exactly what you are producing.

If your batteries were not used much and spent most of the time floating your settings would probably be fine but you are using significant power and you may be compromising much of the later point of the charge cycle. With all controllers you need a bit of manual intervention so keep an eye on the sg. Simple controllers need a bit more watching than the clever ones.

Flux

[trentman]

hi flux thanks for your input

i have set the charge controller to accept 29 volts and then cut of at

28

i have another question for you

i let the batteries stand for a few hours and they still read 25.6 volts

which i thought is a fully charged battery yet the sg level is low at 1.17

why is this

regards mark

[jimjjnn]

Sounds like your acid is diluted or the SG tester is bad. Others on the board here can help you much better than me.

[Flux]

Jim may be right. Some hydrometers are not particularly accurate. If you can compare it or are sure it is correct then there could be several issues.

The only sure way is to check the battery sg when new and fully charged and that should be your future reference and if the figure is way off the manufacturers figure then it should be corrected then.

If you don't have this reference then things are difficult. Ideally charge the battery on a charger at a fixed current enough to make it gas reasonably and check the sg every hour until it ceases to rise. That then should be in the ball park for the makers figure. If it is wildly low then you have to decide if the acid has been spilt and diluted ( or was never correct) or possibly the battery is badly sulphated. The only sure test to see if it is sulphated is to do a full discharge test from fully charged and see if the Ah figure is near nominal.

If you are not in a position to do these things then it may be safer to accept the sg figure as being the fully charged value for that battery. It may be ok to correct it to makers figures but unless you are really sure of the true cause it may lead you into more trouble.

Engine starting batteries need a high sg to get the resistance low enough for cranking amps. Stationary batteries usually work with a lower sg and diluting the acid even more may not be that detrimental, but wildly low figures may have ill effects. Excessively high figures will seriously reduce life and lead to plate corrosion and other problems.

Voltage is not a good indicator of state of charge, and depends to a fair extent on the plate alloying components. Keep charging until sg fails to rise and treat that as full charge. You then have a voltage and sg reference.

Flux

[jimjjnn]

Flux,

I forgot to mention that the Hydrometer should also be temperature compensating.

My error. Sorry.