Inverter / Generator question

[comsense]

Hi all,

I have a motorhome with an old  Generac impact 36lp. It is from around '98 but only has 40 hours (or so the meter says). It recently stopped working, I tried to start it after not using it for a couple of weeks and it won't start at all. The starter motor turns it over but it doesn't seem to fire at all.

I've heard on the grape vine that this model is basically a very bad model that has consistently had problems. Took it to a generator guy who took one look at the model and said he wouldn't touch it , and said I'm better off getting a second hand Onan.


Anyhow, we are travelling on a budget and don't really have the money, and also we don't really use the generator much at all. Perhaps only used it 6 times over  5 months, and we are currently travelling fulltime.

We have been getting along without it for the last couple of months but the one thing we do miss is being able to use the microwave occasionally for lunch/dinner where we don't have hookups.

So......
What I did notice about this model is that it seem to have a separate inverter in a box mounted separately to the generator. I've been trying to research what the inputs and output s of the inverter are to see if I could simple reuse the high power inverter from the generator to run the microwave for short periods off battery. From what I can see the generator supplies a DC? input into the inverter which then supplies the house AC system. I thought it was a 12V DC output to the inverter from the Generator which would be easily replaced with a battery output..  But it didn't seem to even power the inverter on when I tried this. It may be a higher voltage DC or am I completely off??

Anyone know anything about this setup / if it may be possible?

The other things that worry me about attempting this are:

• I know that there must be a charging circut for the house battery hooked into this equation somewhere, and I don't know what it means if I'm basically trying to charge the battery off it's own current in a circular fashion. If I can locate how this works I can easily disconnect.. Maybe?? This may not be a problem if the charging occurs directly off the generator DC output, but I have the feeling that there is a AC to DC converter in the rv running to power the 12V systems when on shore power. My bet is that this is what is used to charge the house battery. In this case my circut would look something like: house battery-> DC to AC Convertor -> AC to DC converter -> house battery ..... This doesn't sound that great!
• AMP draw might be an issue, if the microwave uses say 10 amps (AC 110V), then around 100amps from the battery at 12V's will be needed, which is possible from a car battery for short periods, but maybe not a deep cycle battery. Also I don't have the wattage spec's for the microwave!

Anyway, you can see what I'm trying to achieve on the cheap any advice or background info would be appreciated.

Thanks

 

[Lou Schneider]

I'd find a different service person.  Your problem is in the engine itself, not the inverter-generator package.  The engine is fairly straightforward - if there's air, fuel and a spark it will run.  If not, it's missing one of those three elements.

If the spark is there, you have a fuel problem.  Most likely the carburetor is gummed up from fuel sitting in it for too long.  Or you could have a bad fuel pump or a cracked rubber hose that's preventing the fuel pump from sucking fuel from the tank (the fuel line runs out from the top of the tank and fuel is sucked out like drinking through a straw).  Any of these should be easy for a competent service person to check and fix.

Forget trying to use that inverter from a battery.  It uses high voltage from the generator (160-180 volts DC), not 12 volts from a battery.  Even without knowing the voltage, looking at the size of the wires running from the generator to the inverter should confirm this.  Wires capable of handling the 100+ amps a 12 volt feed would require are bigger than your car's battery cables - at least as big around as your thumb. Higher voltages mean the wires carry less current for the same power.  If the generator to inverter wires are smaller, then they must carry higher voltages.

If you don't want to fix the generator, your best bet would be to buy a stand-alone inverter in the 1500-2000 watt range.  You can find these in truckstops and auto supply stores for $200 or less.  But you'll also have to add several batteries to get enough power to run the microwave - a single battery may supply the power for a few minutes, but while it's doing this it's voltage will drop below the inverter's minimum - just the same as when your headlights dim while cranking a car engine.

Most generators don't have battery charging outputs.  What they do is supply AC power to your converter, which makes 12 volts to run your lights and charge the battery in the same manner as when you plug into shore power.  If you're using an inverter, you will have to keep it from powering the converter.  Wire it so it only feeds some of the circuits in the RV, or if it feeds everything, unplug the converter or shut off it's circuit breaker to break the loop.

 

[comsense]

Thanks for the reply. The generator guys said these gen's have issues with their ignition system. The cost to take the gen out, find the problem, replace the parts would be about $500, but he couldn't guarantee if further than "the end of the street" as it was likely to die again in no time with same or similar problem. In know the fuel pump is working, you can here it, plus smell it if you run the fuel prime. If you they to start it for long enough you will get and loud backfire. So it seems tee spark is firing at least sometimes!  In can't  get at the top of the gen to check the spark, requires removal unfortunately. Do they have a complicated ignition system due to the variable power requirements / throttle control?

 

[Bob Maxwell]

Google Generac ignition problems. Over on the GMC board those with Generac gensets writ about them a lot. 

Google "Generac ignition problems."

 

[Gary RV_Wizard]

Inverter generators typically run on 24 or 48 volts DC. Much more efficient that way. However, I have no idea what that model of Genrac does. It is an LP fuel genset, though. Here is the spec sheet on it.

http://www.generac.com/PublicPDFs/15971.pdf

I hate to ask, but is there a shut-off valve in the LP line to the genset? Sometimes the simple things get overlooked...

 

[comsense]

The model is actually a Generac Impact 36 NP, sorry not LP. It's running petrol and you can hear the fuel pump and smell the fuel so I don't think it's a fuel supply issue.

From googling a little, it seems these units have lots of issues with the iginition sensor which is buried deep inside the motor somewhere and requires disassembly of the engine to replace.

Bugger.

Brad

 

[Gary RV_Wizard]

See if you can find a service and diagnostic manual here. There are a couple that cover various "NP" models.

http://www.generator-parts.com/

 

[Thomp]

Don't know if this is helpful, just repaired my FIL's Generac 36+ Inverter. In the process I made a schematic for the Inverter, posting it here if it helps someone. Keep in mind that not all the board devices were labeled, I did my best to guess what they were. Those that were identified are shown.

Tom

 

[Lou Schneider]

Thanks, Tom!  I'm sure this will be very helpful to others in the future.  I saved a copy to my hard drive for future reference.

And welcome to The RV Forum!

 

[Debr]

Don't know if this is helpful, just repaired my FIL's Generac 36+ Inverter. In the process I made a schematic for the Inverter, posting it here if it helps someone. Keep in mind that not all the board devices were labeled, I did my best to guess what they were. Those that were identified are shown.

Tom

Thank you Tom this was very helpful.
I was wondering if you know of a replacement inverter that would work for this generator?

 

[Mark_K5LXP]

From what I know of these things, the "inverter" described here is a regulator to control armature current, which will then regulate the field and thus the generator output. It'd be highly unlikely there'd be a plug and play replacement other than another one identical to it. For something this old you're soundly in the "DIY" department. One can try and scrounge a salvage unit, track down a competent repair guy or dig into the innards of the thing yourself. It's unknown if the regulator is even the issue, one would have to do some troubleshooting to see if it might be ignition or other problem. For occasional "microwave use" a $400 chinese suitcase inverter genset would easily check the box, so one has to decide how much time and effort to put into a 20+ year old generator needing potentially unobtanium parts vs $400 replacement.

Mark B.
Albuquerque, NM

 

[Debr]

Hi Mark,
This is what blew on the inverter .
The generator runs just fine but it won't power the coach without it.
I was looking to see if anyone had one and did a replacement on one.
My son replaced the fuse so we'll see if it works.
I know it's old but a new generator is about 4,000.00
Here's hoping

 

[Mark_K5LXP]

You might get lucky and replacing the cap will resolve it. Generally when one pops they're all suspect, since they do age out. The standard practice when refurbishing an old supply is to replace all the electrolytics while you're at it, they're not expensive and most of the work is in getting the unit in a position to service it. While it's on the bench one can inspect things for corrosion, loose hardware, bad solder joints, loose connectors and all the myriad of things that causes "vintage" equipment to fail.

Mark B.
Albuquerque, NM

 

[stedyblazin]

Thank you Tom this was very helpful.
I was wondering if you know of a replacement inverter that would work for this generator?

Hey Debr do you still have this generator?

 

[Larry N.]

Debr hasn't been back for over two years.