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Author Topic: Battery Voltage Question - 24v system  (Read 3380 times)
DROdio
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« on: April 08, 2006, 11:19:28 AM »

So I am just now hooking my Xantrex inverter up to my battery bank.

I have 10 deep cycle/marine 115 amp 12v batteries.

My question is this:  In the Xantrex documentation it states that the battery is at full charge at 12.7 VDC.

However, it says that when recharging the batteries, the "bulk volts" charge setting should be at 14.6 VDC, and the "float volts" setting should be at 13.4 VDC.  (And the "equalization" number is a whopping 15.5 VDC!!!)

So my question is, why is it telling me to charge them up so far past 100% Huh?

Also, is anyone by chance hooked up to a Kubota generator & Xantrex inverter?  I can't quite figure out how to get the inverter to start the generator.

Thanks in advance!

DROdio
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« Reply #1 on: April 08, 2006, 11:38:56 AM »

So I am just now hooking my Xantrex inverter up to my battery bank.

I have 10 deep cycle/marine 115 amp 12v batteries.

My question is this:  In the Xantrex documentation it states that the battery is at full charge at 12.7 VDC.

However, it says that when recharging the batteries, the "bulk volts" charge setting should be at 14.6 VDC, and the "float volts" setting should be at 13.4 VDC.  (And the "equalization" number is a whopping 15.5 VDC!!!)

So my question is, why is it telling me to charge them up so far past 100% Huh?

Also, is anyone by chance hooked up to a Kubota generator & Xantrex inverter?  I can't quite figure out how to get the inverter to start the generator.

Thanks in advance!

DROdio

First off, I see a big problem. Your heading says 24 volt system. If that is so, why do you have a 12 volt inverter and why are you worrying about 12 volt charge voltages?

In general, the more your batteries are discharged, the higher the voltage applied to try and rapidly (without boiling) recharge them as fast as possible. As they get closer to full charge the charge voltage is reduced proportionally.

The float voltage is the voltage that may be applied to them continuously without doing any damage to them. If the float voltage is removed for approximately 24 hours the open cell battery voltage will drop to approximately 12.7 volts. (2.12 volts per cell).

The equalize voltage is a higher voltage applied occasionally when the batteries get badly sulphated.

Not trying to be a smart @ss or to hurt your feelings but I strongly recommend you get something like David Smeads book on DC systems before you proceed any further. There is an awfully lot you need to learn about DC systems I think.

Richard
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DROdio
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« Reply #2 on: April 08, 2006, 11:46:28 AM »

Thanks for your thoughts!

Actually it IS a 24v system; i had forgotten i put that in the subj. line and was just using 12V numbers for simplicity since they are 12v batteries (they are arranged in a 24v configuration).

The ACTUAL values are multiplied by 2.  So here are the ACTUAL numbers:

The inverter manual is suggesting the vollowing values:

The Bulk volts is to be set at 29.2 VDC
The Float volts is to be set at 26.8 VDC
And the Equalize volts is to be set at 31 VDC

I have a Xantrex SW4024 MC2 inverter - yes a 24 V system.  Witha 20,000 watt Kubota generator providing the inverter with 120 Volts AC in.

And so my question remains:  If a 24V battery is at 100% at 25.4 volts, why is the bulk charging period so much higher?

And is 31V too high for equalization?

I just want to make sure I don't damage the batteries.

YES I have a lot to learn, I will look for David Smeads book

Thanks,

DROdio
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« Reply #3 on: April 08, 2006, 02:46:09 PM »

Thanks for your thoughts!

Actually it IS a 24v system; i had forgotten i put that in the subj. line and was just using 12V numbers for simplicity since they are 12v batteries (they are arranged in a 24v configuration).

The ACTUAL values are multiplied by 2.  So here are the ACTUAL numbers:

The inverter manual is suggesting the following values:

The Bulk volts is to be set at 29.2 VDC
The Float volts is to be set at 26.8 VDC
And the Equalize volts is to be set at 31 VDC

I have a Xantrex SW4024 MC2 inverter - yes a 24 V system.  With a 20,000 watt Kubota generator providing the inverter with 120 Volts AC in.

And so my question remains:  If a 24V battery is at 100% at 25.4 volts, why is the bulk charging period so much higher?

And is 31V too high for equalization?

I just want to make sure I don't damage the batteries.

YES I have a lot to learn, I will look for David Smeads book

Thanks,

DROdio

OK. That makes more sense now.

The 15.5/31 volts is equal to 2.58 volts per cell. This is an equalize voltage to be used only when you are having battery problems when they will not hold proper charge or the different cells are holding different voltages due to internal sulfation or other causes. Not to be used indiscriminately. Read the book first before you do this. It is generally only for a limited number of minutes/hours and i can not remember for sure. I repeat that equalize is only to be used sparingly and only occasionally. Probably never more often than every few months.

The 14.6/29.2 bulk charge is equal to 2.4 volts per cell. This is the initial charge applied when the batteries have been discharged significantly. A good charger will also monitor the cell temperature to prevent you overheating the battery and boiling out the water and destroying the battery. I suspect your inverter has this feature available as an option at least.

I explained earlier that the float voltage is the safe voltage that can be applied continuously without doing any damage to the battery.

I mentioned cell voltage and that is because many battery manufacturers rate their batteries at a certain cell voltage since batteries (the complete unit) may contain 2, 4, 6 or more cells depending on the voltage desired.

I suspect that your inverter will not start your genset until the battery is discharged to a sufficient level, that you can pre-set I believe, and that level would probably be in the 11.9/23.8 (2 VPC) voltage range.

Richard
« Last Edit: April 08, 2006, 04:56:53 PM by DrivingMissLazy » Logged

Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
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