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DC Generator Question
By bprobinson, Section Homebrewed Electricity Posted on Fri Nov 25, 2005 at 09:35:46 PM MST
DC Generator Charging Battery Bank

We recently attached a newly constructed 80 Amp DC Generator to our brand new Trojan T-105 battery bank. All was good until just the other day. The batteris were low, probably 40% or so and the DC Generator was putting out 13Volts. We ran it several times with this output. Now, it's still putting out 13v, but the minute we attach it to the battery bank it drops to 11 volts! We're good on the 13v right up to the connections to the battery bank. We have checked all connections, we're running straight through 6 gauge to the generator. Anyone have any idea what could be causing this? One more thing, the batteries are reading exactly 11 volts as well...which seems a little weird but could be coincidence?

DC Generator Question | 13 comments (13 topical)

Re: DC Generator Question (3.00 / 0) (#1)
by Reno on Fri Nov 25, 2005 at 03:26:46 PM MST

It is being pulled down by the voltage of the batteries. Leave it run the voltage will rise as the batteries charge.

Re: DC Generator Question (3.00 / 0) (#2)
by Flux on Sat Nov 26, 2005 at 02:51:22 AM MST

Need much more information on the generator and how it is controlled to help much.

Reno may be right but an 80A generator should raise it fairly quickly.

13v is too low to charge a 12v battery unless there is something in your voltage readings such as being rectified ac that makes it nonsense. Sounds as though you have a high resistance connection inside the generator somewhere. Try a big head lamp bulb across the generator output and see if it lights and how many volts you get across it.

Flux

[ Parent ]

Re: DC Generator Question (3.00 / 0) (#3)
by Scotth on Sat Nov 26, 2005 at 08:28:27 AM MST

I am far from an expert,but isn't 11 volts really low for a brand new battery bank?

Re: DC Generator Question (3.00 / 0) (#4)
by finnsawyer on Sat Nov 26, 2005 at 08:51:12 AM MST

You need to measure the current flowing into the battery bank. While the generator may be rated for 80 amps, it may put out only a fraction of that into a load at 11 volts. Scrounge up a 50 or 100 amp truck ammeter and put it in series with the batteries. You also shouldn't discount the possibility that one of the batteries has developed a bad cell. Measure the voltages of all the batteries. They should all be the same. If one is lower than the others it will probably be the culprit.
GeoM

Re: DC Generator Question (3.00 / 0) (#5)
by K3CZ on Sat Nov 26, 2005 at 12:11:12 PM MST

Following the thread introduced by #4 above, I question whether the generator is putting out any amps at all; the symptoms agree with that surmise. Anyhow, significant battery charging will not occur until a solid voltage source (the generator) is connected with at least 14.0 volts available. 14.4volts will top off the charge (at room temperature)on the batts and will represent the max float charge level that is desirable. 13.6 volts is often mentioned as a desirable float level, but will maintain the batteries at only about the 50% charge level. I would suggest reading a good book on lead acid battery maintenance; the significant information has not changed much since 1910 or so.
Good luck; VAN K3CZ, PE

Re: DC Generator Question (3.00 / 0) (#6)
by bprobinson on Sat Nov 26, 2005 at 04:54:52 PM MST

First off...I want to thank everyone that responded. Warning - This one's a little long winded so you may want to skip it!
We've since discovered that the meter we were using was reading incorrectly. We've tried two other meters that both read 12.1 or 12.2 while ours still read 11. We've also tested every 6 volt battery individually and each read 6v or better. We then tested the DC Genny (with no load) and it was putting out between 13.9 and 14 on the new meters. We attached the Genny to one set of 6 volts and it still put out 13.9. We hooked in 2 more, and it dropped a bit to 13. So we put it all back together and we were right back where we started from. It's only putting out 12 when hooked to the total bank of 8 T-105s. We tried it with no load, and with full load. No load made no difference, the gauge dropped under full load while charging. We have nothing but straight through 6 gauge running directly to the well grounded genny...no controller or anything (yet). When the batteries came in last week they were not fully charged and only read 5 volts each. That was when the genny put out 13-14 volts. Now that they're up to 40-50% (and 6v each) we have a problem, could it be that the 80 amp Genny just isn't enough? I know we require a 90 amp to equalize at C20 (1800 amps/20) but I was hoping this would get us by until we could get a higher amp alternator.

Re: DC Generator Question (3.00 / 0) (#7)
by hiker on Sun Nov 27, 2005 at 01:46:01 AM MST

might have a week rectifier in the gen--
WILD IN ALASKA
[ Parent ]

Re: DC Generator Question (3.00 / 0) (#8)
by Flux on Sun Nov 27, 2005 at 01:47:55 AM MST

First thing to do is to get an ammeter and actually measure what the genny is putting into the battery under those various conditions.

What is this generator, it is obviously voltage regulated, is it a car alternator?
Is it belt driven and are the belts slipping at full load, is it being driven fast enough. Is it some bought in generator of some completely different type.

If you are using a car alternator to charge that large battery bank I would suggest you remove the regulator and supply the field through a resistor to give a suitable charging current. There has been a fair bit of discussion about this here.

It may be that the internal regulator is clever and reducing the volts as things warm up, it may think it is a car battery and ought to be charged by now.

True 80A should do your job quite easily with no load so something is wrong. If it is a car alternator the 80A will be short term rating and if you remove the regulator you may have to keep the current down to stop it over heating but it should still do the job.

If it is any other type of generator you will have to give more details.

Flux

[ Parent ]

Re: DC Generator Question (3.00 / 0) (#9)
by bprobinson on Sun Nov 27, 2005 at 06:05:00 AM MST

Thanks for the input...I'll check through the forum for info on disabling the regulator and adding a resistor. We are using a car alternator with an 11hp Briggs & Stratton - our own DIY DC Genny. I've got a document from Home Power that states that a newer alternator may be a problem...we thought we had an older one but I think now that that is really the problem.

[ Parent ]

Re: DC Generator Question (3.00 / 0) (#10)
by wdyasq on Sun Nov 27, 2005 at 08:24:01 PM MST

80 amp car alternator will toast if it is pushed that high for long.

Ron
Adventure is just bad planning." -- Roald Amundsen
[ Parent ]

Re: DC Generator Question (3.00 / 0) (#11)
by bprobinson on Tue Dec 20, 2005 at 02:25:09 PM MST

Thanks for all your input. Did as suggested (here and other places). We brought the Alternator to Herbie the alternator guy and had him disable/deactivate the internal regulator. He tested it for us again...80 Amps, up to 18 Volts. We purchased a 25 Ohm rheostat and wired it in to the positive and "field" connections of the alternator (after hooking it back up to the 11HP motor/frame). Grounded it. Started the engine, turned up the resistor, watched the voltage meter make a quick jump to about 13, and then right back down to where it was before, at about 12.2 v. And there it sat for over 1/2 hour. Adjusted the rheostat and it made no difference. So, we took the rheostat (resistor)out of the equation and wired it direct. I just wanted to see the damn thing work. Even with no regulation, we got nothing but 12.2v. So now we have an 80 Amp DC Generator that will only put out as long as it's attached to anything BUT our 8 - T105's.
I read somewhere in here that the batteries will make the voltage drop to their level, but amps go up??? Am assuming this is why we need an amp meter?

Thanks

[ Parent ]

Re: DC Generator Question (3.00 / 0) (#12)
by ghurd on Tue Dec 20, 2005 at 02:47:29 PM MST

IMHO, any 'reasonably controlled charging' with a car alternator is a bitch.

Remember that a big battery will take a lot of amps as the volts rise ("the batteries will make the voltage drop to their level"). The amps should go up.

An ammeter will tell if there is charging happening. 80A is a lot either way.

G-
Ghurd.info
[ Parent ]

Re: DC Generator Question (3.00 / 0) (#13)
by bprobinson on Wed Dec 28, 2005 at 12:29:21 PM MST

Thanks, this appears to be what was happening. We though we should see the volts go up, not amps.

[ Parent ]

DC Generator Question | 13 comments (13 topical)

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