Home generator overcharging battery?

Fred Werring · Dec 8, 2018

Got an 8000w Rigid generator, 8-9 years old, with a Robin/Subaru gas engine, electric/pull rope start. Just wanted to change the oil and let it run for a while.

Old battery was bad, pull started the engine...only 2 pulls to start it after a year and a half, I was impressed.

Checked voltage at the (old)battery while running, started out at about 14 volts. Checked a half hour later, my digital Fluke was showing 48VDC. Not cool. Checked with a cheapo analog meter, same thing.

Rang out the rectifier/diode block. Diode and ohm check looked good, could only read through one way on the DC leads on the rectifier. Had a friend bring his scope meter, it showed spikes around 60VDC.

Got a new battery, starts charging at 14 volts, half hour later was 16.6 volts at the battery. Haven't put the scope meter on with the new battery.

Time for a new diode/rectifier? Part description doesn't say anything about voltage regulation, and there is not a separate regulator in the circuit.

Something going on with the engine coils/magneto?

Thoughts?

Thanks

Fred

Steve@Advance · Dec 8, 2018

This is just a guess, not familiar with that particular model...

But most small engines that don't have a regulator, just a low amp charging system, will not be capable of producing those kind of overcharge voltages. Possibly this has a 12vdc output connection, and therefore has some kind of regulator, probably built into the rectifier.

Fixing it right is always the first choice, but if the part is unavailable, or over priced, you could disable the charging system, add a battery tender. Let it keep the battery charged when not in use, then switch it over to the AC power from the generator to keep the battery up when running. I suspect the ignition is magneto, separate from the battery or charging system, so once started the ignition is not dependent on the charging system.

Billy Shafer · Dec 8, 2018

Model and serial number would help. To look up the prints and service manual.

guido · Dec 8, 2018

Hello Fred Werring,

There may not be a voltage regulator. You should check how many amps it is charging. Anything more then a couple of amps is too much. Bet you is less then one amp, and it won't hurt the battery, even @16 volts,

Guido.

Janicholson · Dec 8, 2018

Are you using an analog meter, or a digital. Pulsed DC will not read correctly unless you have a $100 digital like a Fluke. They try, but do not do well. I thnk the old battery was open, and allowed the charging system to see no functional load. Use an old meter and see what is really happening. Nice Idea to look at a scope trace, but they are just interesting sometimes. Jim

Geo-TH,In · Dec 8, 2018

Two quick fixes.

One fix, use diodes in series to reduce charging by 0.6 to 0.7v per diode.

Two, don't use 12v charging system from generator, instead connect a smart charger to Generator's 120 vac out to charge battery. This would be the easiest fix and no fear of overcharging.

Russ from MN · Dec 8, 2018

Another cheap fix, disconnect the charging system and get a small maintainer and plug into your line power, as long as you store it in a location with power. Then it will always be ready to go as long as the battery is good. I imagine the engine runs on magneto ignition so it doesn't need the battery to run, and it will start many times on a good battery.

Bob · Dec 8, 2018

Seems like you may have an unregulated charging system.

SURPRISED, tho, that such a system would push the voltage across a "good" battery that high, but perhaps so.

Does the battery warm up and slobber on itself?

tn terry t · Dec 8, 2018

(quoted from post at 17:09:36 12/08/18) Model and serial number would help. To look up the prints and service manual.

I would bet money I have one just like it. mine was built in 2009 model# is RD8000 if that helps any

MarkB_MI · Dec 9, 2018

Your generator might have an unregulated DC output. As for the 48 volt measurement, that would be unusual for a GOOD battery. I suspect your battery is bad.

If you look up the part for the rectifier, is it described as a "rectifier" or a "regulator/rectifier"? If it's the former, most likely it's unregulated. If it does use a rectifier/regulator, note that most small engines use a "shunting" regulator. A shunting regulator shorts out the alternator output each time it exceeds the regulated voltage. Typically the alternator has a three-phase output, so this happens three times per engine revolution (maybe six times per rev, depending on the design). It takes a finite length of time for the solid state switches in the regulator to turn on, which would explain the spikes visible on your friend's scopemeter. You would not see them if the battery was good and you had a good connection to the battery.

MarkB_MI · Dec 9, 2018

Does your "rectifier" look something like this? <a href="https://www.ebay.com/p/OEM-Robin-Subaru-15-Amp-Voltage-Regulator-263-71903-a1/12011656777">https://www.ebay.com/p/OEM-Robin-Subaru-15-Amp-Voltage-Regulator-263-71903-a1/12011656777</a>

That's a single-phase shunting rectifier regulator. You can replace it if you like, but I suspect you'll see exactly the same thing with a new one.

Texasmark1 · Dec 9, 2018

48 Volts sounds like induced interference (spark plugs-wires) or a problem within the multimeter. Got an old Simpson analog? You have to have a mechanism to develop a voltage of that magnitude from an otherwise unregulated 16 DCV source. I don't see that happening with a pair of diodes (or even a 4 diode FW bridge rectifier) and a transformer....too few parts for doubling, tripling.

I find sealed batteries tolerate overvoltages better than the old style with caps/plugs. My generator is on LP, starts quickly, runs once per week for 15 minutes, is regulated and puts out at around 14.5 and with the old style batteries I had venting. Replaced with a sealed battery and that was that.....just a lot of charging for the limited weekly starting power consumed.

Fred Werring · Dec 9, 2018

New and old batteries are the sealed gel type.

That's what is bugging me too...that much voltage

Fred

Fred Werring · Dec 9, 2018

My Fluke is decent, model 29, should be able to handle it. Never had an issue with it on any other engines.

Only analog I have anymore is a $10 cheapie, and it shows the same readings.

According to the print, just looks like a FW rectifier, no regulator

Fred Werring · Dec 9, 2018

Images of the print and replacement rectifier below.

Just looks like a full wave rectifier to me, no voltage regulation, but maybe the mfg isn't showing everything inside that little black box.

The meters I used were a Fluke 29 and a $10 cheapo analog, both read the same voltages...16.6 VDC at the new battery after about a half hour running.

I may go ahead and put a new rectifier on it. It doesn't check bad with the meter, but I can't figure anything else causing those spikes observed with the scope. Maybe 1 diode in the rectifier is bad.About $35 delivered, but I'd prefer to have it right.
Or maybe if that doesn't work I'll put in a battery disconnect switch I can turn off after I get it started. The battery/charge system has nothing to do with the ignition.

Thanks

JMOR · Dec 9, 2018

(quoted from post at 12:26:01 12/09/18) Images of the print and replacement rectifier below.

Just looks like a full wave rectifier to me, no voltage regulation, but maybe the mfg isn't showing everything inside that little black box.

The meters I used were a Fluke 29 and a $10 cheapo analog, both read the same voltages...16.6 VDC at the new battery after about a half hour running.

I may go ahead and put a new rectifier on it. It doesn't check bad with the meter, but I can't figure anything else causing those spikes observed with the scope. Maybe 1 diode in the rectifier is bad.About $35 delivered, but I'd prefer to have it right.
Or maybe if that doesn't work I'll put in a battery disconnect switch I can turn off after I get it started. The battery/charge system has nothing to do with the ignition.

Thanks

<img src="https://www.yesterdaystractors.com/cvphotos/cvphoto5422.jpg">

<img src="https://www.yesterdaystractors.com/cvphotos/cvphoto5423.jpg">

The diodes are constantly switching on & off, at least 2X per cycle and 'switching' creates transient voltages.....it is normal & just the way diodes work. Nothing to worry yourself about.

MarkB_MI · Dec 9, 2018

It appears the DC output is unregulated. Regulator-rectifiers normally have a metal case to help sink heat.

The behavior you see is consistent with an unregulated alternator. The battery, if it was good and also properly connected, should suppress any spikes coming out of the alternator. It is quite normal to see big voltage spikes if there is no battery connected to the alternator, or if the battery is bad.

Home generator overcharging battery?

Fred Werring

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Steve@Advance

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Billy Shafer

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guido

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Janicholson

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Geo-TH,In

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Russ from MN

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Bob

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tn terry t

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MarkB_MI

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MarkB_MI

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Texasmark1

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Fred Werring

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Fred Werring

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Fred Werring

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JMOR

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