Community Forums

zzjea · 07-02-2013, 07:46 AM

My Generac 75D won't crank but just tries to like it is not getting enough amps. It has cranked and run fine in recent weeks. I do use the preheat switch before trying to start.

I believe the 4 6v house batteries are powering the gen starter. I also have 2 chassis batteries that I don't think are related to this issue. Although, I have tried the Boost switch when cranking but no change.

What is the best way to determine if there are enough amps getting to the gen? I have cleaned all the contact points that I can find including the battery terminals. I am getting 13.2v at the gen + stud bolt.

Is there a test I can do to determine if it is the battery bank or the gen itself? All house 12v items function properly and the wall control panel shows the batteries are fully charged.

I would prefer not to disassemble the battery bank and take each one some place to have it load tested if I can avoid it.

Thanks,

John

BFlinn181 · 07-02-2013, 10:15 AM

I think you could start by disconnecting the 4 batteries and check voltages of each battery. If you determine a significant difference in each battery, then haul them out and have them load tested. You could also do a specific gravity test on each cell to determine if you have bad cells or batteries. The SG test doesn't require disconnecting the batteries. You could also disconnect generator and jump start it with a known good 12 v battery to see if it starts on that. If it doesn't, I'd then suspect the generator starter or start circuit.

zzjea · 07-02-2013, 11:01 AM

Quote:

Originally Posted by BFlinn181

I think you could start by disconnecting the 4 batteries and check voltages of each battery. If you determine a significant difference in each battery, then haul them out and have them load tested. You could also do a specific gravity test on each cell to determine if you have bad cells or batteries. The SG test doesn't require disconnecting the batteries. You could also disconnect generator and jump start it with a known good 12 v battery to see if it starts on that. If it doesn't, I'd then suspect the generator starter or start circuit.

THANKS. I will try one or more of these ideas.

wb7auk · 07-02-2013, 11:14 AM

A easy way to check the cranking voltage at the genset is have someone try to start it
and you look at the voltage at the genset. should be above 11 volts while cranking.

harris155 · 07-02-2013, 01:35 PM

My neighbours RV has a similar problem and they always come to me for repairs.
They have a Fleetwood on a Sprinter Chassis with an Onan Diesel Generator.
Unless the Chassis battery is right up to 100% or the engine is running the generator will blow the 175 Amp Buss Fuse.
All the connections have been cleaned.
Seems inconvenient to start the engine just to boost the battery so you can start the generator to charge the battery.
At 20 dollars a pop getting a little pricey as well.
I wonder if a heavier gauge cable should be run straight from the battery to generator rather than being switched by all the relays in the chassis electrical system.

clyon51 · 07-02-2013, 03:38 PM

I would go right to the generator's ground on the chassis frame, the main problem with generator cranking.

wa8yxm · 07-02-2013, 06:41 PM

To see if there are enough amps to the genny measure voltage AT the generator while cranking. If it does not change the problem is in the generator, If they drop to like 3 the problem may still be in the generator. But is more likely "Up-stream".

BFlinn181 · 07-02-2013, 06:53 PM

I believe clyon51 is on to something, If you have a poor ground between the generator and the frame (ultimately the batteries) you'll have starting issues. Check ground strap between generator and frame / battery. A quick test before unbolting and wire brushing everything would be to use a jumper cable between generator frame and negative battery or RV frame and try to start. If it turns over faster, you know the ground is the issue.