12 Volt Electrical / Battery Question

[JD 4520]

I have a three year old Cummins all house generator. It has a new 12 volt battery within the past two months. Today I went out to test start the generator and discovered that the battery was dead. I jump started it with my truck. It started right away, then I disconnected the jumper cables at which point the generator stopped. I reconnected the jumper cables, started right up, waited approx one minutes and disconnected the jumper cables; the generator stopped again. The third time I reconnected the jumper cables, started the generator, ran it for 3 - 5 minutes, disconnected the jumper cables and this time it continued to run just fine. I now have the maintainer charger on and will leave it on for several days.

Q: Why would the generator stop running as described above just because the battery was low?

 

[whistlepig]

I have a three year old Cummins all house generator. It has a new 12 volt battery within the past two months. Today I went out to test start the generator and discovered that the battery was dead. I jump started it with my truck. It started right away, then I disconnected the jumper cables at which point the generator stopped. I reconnected the jumper cables, started right up, waited approx one minutes and disconnected the jumper cables; the generator stopped again. The third time I reconnected the jumper cables, started the generator, ran it for 3 - 5 minutes, disconnected the jumper cables and this time it continued to run just fine. I now have the maintainer charger on and will leave it on for several days.

Q: Why would the generator stop running as described above just because the battery was low?

Is this a diesel generator?

 

[JD 4520]

Is this a diesel generator?

It is a Natural Gas Generator.

 

[whistlepig]

It is a Natural Gas Generator.

Then it has spark plugs that require electricity. If your generator has a charging system it sounds like this charging system is failing. Both to charge your battery and provide enough electricity to fire the spark plugs.

 

[Travelover]

You could put an ammeter between the battery and charging wire to see how much output is there. Of course, if the engine dies as soon as the battery is disconnected, the unit is not charging.

 

[jinman]

Gary, your battery was so discharged that it took all the capability of your generator's charging circuits. In other words, the discharged battery was loading down the 12 vDC section of the generator so much that it could not supply the ignition with power. You had to keep your jumper battery attached long enough that the internal battery took on some charge and the current load dropped a bit. If you had completely disconnected the internal battery and only had the jumper battery attached, it would have kept going when you remove the jumper battery because there would have been no load on the charging system.

Also, you obviously have something wrong with the generator that is causing it to drain your starting battery. I would invest in one of those battery terminal mounted disconnect switches to open the battery circuit when not in use. Unless you can find the drain on the battery, you'll keep having this problem over and over. You may have a leaky diode or partial short in the circuit that is allowing the battery to slowly drain over time.

 

[Travelover]

.......... You may have a leaky diode or partial short in the circuit that is allowing the battery to slowly drain over time.

Or the generator is not charging the battery. Again, an ammeter between the battery and the charging wire will show charging rate and discharge rate, due to a leak or short.

 

[jinman]

Or the generator is not charging the battery. Again, an ammeter between the battery and the charging wire will show charging rate and discharge rate, due to a leak or short.

An ammeter is a bit of a pain to install without an inductive pickup. A simple voltmeter reading will tell if the generator is putting out enough to charge the battery. Since he said it maintained after keeping the jumper battery in place for a few minutes, I'd bet the battery is being charged. Remember if his battery is dead, it will be a huge load on the charging circuits. Their response is to drop the voltage to limit current. After the generator will run by itself, I'd let it run for 10 or 15 minutes and check the voltage across the battery leads for greater than 12 volts. When the battery is fully charged, the voltage should read 13.85 to 14 volts with the generator running and around 12.5 volts after the generator is shut down. As with automobiles, voltage monitoring of the charging system is far more common than current monitoring in modern instrumentation. There's nothing wrong with what you are suggesting except it's just more difficult in my opinion.

Edit: Your suggestion of checking leakage current with an ammeter is a good one. Most ammeters have low current capability and would show the drain. I would not use the same ammeter for looking for a small drain as I would to monitor charging current.

 

[Phils]

My generator's electronics will kill the little battery (Kohler-powered propane 10KW) in a few weeks unless the generator is run. There is a little 'computer' but since it uses LED numerical readings, I knew from the start it wouldn't be as efficient as one using LCDs.

I added a second little battery, doubling the reserve, and put a 60 watt solar panel on it and haven't had a problem since.

As the OP mentioned, a battery maintainer would be a good idea (like the little Battery Tender). I'd just leave it connected rather than connecting it for a few weeks on and off.

Phil

 

[Travelover]

A...........I would not use the same ammeter for looking for a small drain as I would to monitor charging current.

Right. I have an automotive ammeter gauge that reads +/- 30 amps with alligator clips, so I can plumb it in easily to check charge rate. For reading the drain current, I'd use a little multimeter, in milliamps.