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Old 06-10-2016, 12:38 PM   #1
KEH
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Generator only starts with shore power

Generator starter is connected to house batteries.
When connected to shore power the generator starts right up.
When NOT connected to shore power the starter drags bad and will not start.

So, I thought when connected to shore power the battery charger must be providing extra juice to the batteries, but with shore power connected and the charger off, the generator still starts fine.

Why is there more juice to the generator when connected to shore power, with the charger off?

Any thoughts would be appreciated.
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Old 06-10-2016, 12:52 PM   #2
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Sounds like your house batteries are not getting a full charge. Check connections and water level.
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Old 06-10-2016, 01:33 PM   #3
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Something else is pulling on the batteries. When you hook it to shore power that load is being taken off the batteries .... You might just have old batteries starting to die on you. ..Just a guess without being there.


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Old 06-10-2016, 02:56 PM   #4
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Do you have an inverter running, with AC loads running off that ?

On shore power that load is transfered off the batteries.

Your house batteries also seem weak.
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Old 06-10-2016, 03:09 PM   #5
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Check the battery voltage with and without shore connected. Check again while cranking the genny. Let us know.
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Old 06-10-2016, 03:16 PM   #6
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Are the Batteries good?
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Old 06-10-2016, 08:01 PM   #7
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Thanks all very much for the input. On Sunday I will work on all of the suggestions and post back here.

I appreciate the direction!
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Old 06-12-2016, 04:33 PM   #8
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Here are the results of the tests:

House batteries feeding generator starter (read at the batteries):
With charger ON: 13.10V
With charger OFF: 13.01V
With charger OFF and trying to start generator : 12.10V and starter dragging bad

Reading at the starter:
With charger OFF: 12.75V
With charger OFF and trying to start generator 9.5V and starter dragging

I used a battery hydrometer and tested each cell of the 4 Trojan T-105 6V batteries and each cell was at the highest (good) specific gravity level of 1300.

I installed a new generator starter a couple months ago. Before then, the starter wouldn't work even when connected to shore power. Now the generator will only start when connected to shore power (or using a jump starter on the house batteries, which I had to do a couple weeks ago while traveling).

I tried using the boost switch to connect the chassis and house batteries, but nothing happened - the switch light didn't come on either. So I have a problem with that too.

The Generac generator service manual says:
Measure the voltage at the terminal of the starter contactor and verify 11-12 VDC is available to the generator during cranking. If voltage is below 11 VDC, measure at the battery terminals during cranking. If battery voltage
is below 11 VDC, recharge/replace battery.

So it appears my batteries need replaced?

Your thoughts are appreciated.
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Old 06-15-2016, 06:34 AM   #9
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Quote:
Originally Posted by KEH View Post
Here are the results of the tests:

House batteries feeding generator starter (read at the batteries):
With charger ON: 13.10V
With charger OFF: 13.01V
With charger OFF and trying to start generator : 12.10V and starter dragging bad

Reading at the starter:
With charger OFF: 12.75V
With charger OFF and trying to start generator 9.5V and starter dragging

I used a battery hydrometer and tested each cell of the 4 Trojan T-105 6V batteries and each cell was at the highest (good) specific gravity level of 1300.

I installed a new generator starter a couple months ago. Before then, the starter wouldn't work even when connected to shore power. Now the generator will only start when connected to shore power (or using a jump starter on the house batteries, which I had to do a couple weeks ago while traveling).

I tried using the boost switch to connect the chassis and house batteries, but nothing happened - the switch light didn't come on either. So I have a problem with that too.

The Generac generator service manual says:
Measure the voltage at the terminal of the starter contactor and verify 11-12 VDC is available to the generator during cranking. If voltage is below 11 VDC, measure at the battery terminals during cranking. If battery voltage
is below 11 VDC, recharge/replace battery.

So it appears my batteries need replaced?

Your thoughts are appreciated.
One other relatively quick item to check that doesn't cost a thing...check your cables between both the house batteries and the coach and the generator and house batteries (and ground to the coach). I had a loose ground wire from the house batteries to the coach that caused the same problem. The house batteries could power other stuff through that loose connection, but couldn't provide the oomph to start the gen. Once I found, cleaned and tightened that ground everything was happy again.
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Old 06-27-2016, 09:54 PM   #10
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Originally Posted by Andy Waddell View Post
Once I found, cleaned and tightened that ground everything was happy again.

Right on. Too often, we neglect the grounds, both at the batteries and at the chassis. Also, it's good maintenance practice to disassemble, thoroughly clean, and retighten the grounds at the frame. I've also replaced the terminal lug.

Then, SEAL the frame ground with paint, or a polysulfide brushable sealant, including the area where the insulation stops and the wire enters the terminal. This prevents future corrosion. I don't recommend liquid electrical tape as it degrades quickly. Spray the battery terminals with that red goop. It actually works.

Sorry, lengthy reply, but I've done this for years and I've already found this on the motor home I just brought home.
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Old 06-28-2016, 06:10 AM   #11
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Thanks much for the replies. I will track down the grounds and clean them up.

I had a golf cart technician test each of the 4 Trojan batteries and he said they are good.

I'm also going to track down the booster relay that connects the house and chassis batteries, since it is not working. Seems that could be part of the problem.

Your suggestions are appreciated.
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