Battery charging formula for new generator

[Troutcreekman]

[inetdog]

I am glad you are laughing, but I do not see anything funny. Am I missing something?
...and welcome to Solar Panel Talk!

[SunEagle]

I am glad you are laughing, but I do not see anything funny. Am I missing something?
...and welcome to Solar Panel Talk!

Might be an inside joke or a lack of communication.

[Shockah]

Astonishing formula left him speechless?

[Troutcreekman]

battery charging calculation for generator back-up

Aloha, I have 8 L-16HC 420 amp batteries, 24v system, 2.4 kw of panels looking for new generator for back-up/charging. Looking at honda eu generators cant afford a diesel right now, how many amps needed to efficiently absorb batteries. Eu3000 Eu 6500? Mahalo for any input. David

[Sunking]

Aloha, I have 8 L-16HC 420 amp batteries, 24v system, 2.4 kw of panels looking for new generator for back-up/charging. Looking at honda eu generators cant afford a diesel right now, how many amps needed to efficiently absorb batteries. Eu3000 Eu 6500? Mahalo for any input. David

For a generator you want to size it to provide a C/8 charge current to the batteries, plus enough to run any loads at the time x 1.25.

C/8 on 420 AH = 52.5 amps. So just for battery alone will require 53 amps x 27 volts x 1.25 = 1788 watts. Add another 1 to 2 Kw and you are looking for around a 4 to 5 Kw minimum genny. You do not want to oversize too much because then you start burning more fuel than necessary. You want to load up the genny to about 75%. Next thing you need to add to your list is a 50 amp 24 volt rectifier running off 240 VAC. Surplus telecom will have a lot of those cheap

[Sunking]

A = ah/8

[Troutcreekman]

Laughter

First post didn't work out quite right here is what I was trying to do. ooopps.

Aloha, I have 8 L-16HC 420 amp batteries, 24v system, 2.4 kw of panels looking for new generator for back-up/charging. Looking at honda eu generators cant afford a diesel right now, how many amps needed to efficiently absorb batteries. Eu3000 Eu 6500? Mahalo for any input. David

[mapmaker]

First post didn't work out quite right here is what I was trying to do. ooopps.

Aloha, I have 8 L-16HC 420 amp batteries, 24v system, 2.4 kw of panels looking for new generator for back-up/charging. Looking at honda eu generators cant afford a diesel right now, how many amps needed to efficiently absorb batteries. Eu3000 Eu 6500? Mahalo for any input. David

Actually, you could get by with a honda eu2000 if you were using it only to charge your batteries. It could provide 50 amps of charging, if you had no other loads.

It may depend somewhat on your charger.... it should be power factor corrected and not have too high a startup surge.

--mapmaker

[mapmaker]

Aloha, I have 8 L-16HC 420 amp batteries, 24v system, 2.4 kw of panels looking for new generator for back-up/charging. Looking at honda eu generators cant afford a diesel right now, how many amps needed to efficiently absorb batteries. Eu3000 Eu 6500? Mahalo for any input. David

Your battery bank is 840 ah at 24 volts. Sunking based his advice on 420 ah at 24 volts, so you would need to double his numbers if you want to follow his advice.

Personally, I think you could manage very well with a Honda eu3000... it depends on whether you want to run other AC loads while you are charging. I have 400 ah at 24 volts and don't even use my honda eu2000 to its full capacity while charging.

One more thing... what are you charging with? Hopefully your charger is power factor corrected and does not have a huge inrush current when it starts charging.

--mapmaker

[Sunking]

Your battery bank is 840 ah at 24 volts. Sunking based his advice on 420 ah at 24 volts, so you would need to double his numbers if you want to follow his advice.

I did not catch that, thanks.

I have 400 ah at 24 volts and don't even use my honda eu2000 to its full capacity while charging.

That tells me your rectifier/charger is too small. Optimum charge rate on a genny is C/8 or 50 amps on a 400 AH battery. A 50 amp 24 volt rectifier will pull just about every bit of 2000 watt genny.

[Sunking]

Actually, you could get by with a honda eu2000 if you were using it only to charge your batteries. It could provide 50 amps of charging, if you had no other loads.

It may depend somewhat on your charger.... it should be power factor corrected and not have too high a startup surge.

Again A = AH/8

As you spotted in his other post he has 840 AH battery and C/8 = 105 amps. He would need a minimum 4 Kw genny running a 100 amp 24 volt rectifier.

[inetdog]

--Mod Note: I think I just merged the two threads which Troutcreekman opened on the same topic.

[mapmaker]

That tells me your rectifier/charger is too small. Optimum charge rate on a genny is C/8 or 50 amps on a 400 AH battery. A 50 amp 24 volt rectifier will pull just about every bit of 2000 watt genny.

Actually, the eu2000 is a 1600 watt (continuous) generator , it can supply 2000 watts for awhile. I charge the batteries with my outback inverter/charger. I've been using this generator for years, charging at C/10 (40 amps). NOTE: when I start bulk, the current is a bit over 40 amps and as I reach absorb (29.4 volts) the current is a bit under 40 amps.

Average voltage during bulk is about 28.5 volts... 28.5 X 40 amps = 1140 watts, well within the generator's capacity. I could easily push my charge rate up to C/8 if I wished.

The battery current is monitored by a trimetric. I'm not sure exactly how efficient the outback charger is, or what is its power factor... I have the outback programmed to draw no more than 12 amps AC from the generator, and to use up to 10 of those amps for battery charging. 120 volts X 10 amps = 1200 watts. It almost seems too good to be true... 1200 AC watts pushing 1140 watts into the batteries.

There are usually 50-150 watts of baseline loads while I am charging... The outback and the generator work well together... if the AC loads exceed 2 amps, the outback cuts back on the charging current (10 AC amps) so as not to exceed a 12 amp draw from the generator.

--mapmaker

[Troutcreekman]

lots of info

Thanks for al the input. so if I bought a eu6500 it is rated at 45.8 amps it would be charging through my inverter currently a trace 4000 watt, soon to be a sunny boy. Does the generator just run full bore and the inverter controls the charge rate. I would just want to use it for the bulk charge seems to expensive for absorbing and floating. Seems complicated figuring the optimum generator size efficiency etc. The eu 3000 is rated at 23.3 amps sounds like it is to small by the numbers. Like to run shop tools ( woodworking 120v) for extended periods during the day how does that effect charging on cloudy days? Sorry lots of random stuff here. David