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 > Onan Micro 4000 Generator Won't Start

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txnese

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Posted: 07/05/18 05:40pm Link  |  Quote  |  Print  |  Notify Moderator

The chassis engine fires right up, so that battery is good. I checked the house batteries with a volt meter and it reads about 12.6 volts. I also checked the generator's starter relay, got 12 volts on input side, and 0 on the output side. I push to start the generator and the output side shows like 4 volts. I was thinking bad starter solenoid, so I used a starter jumper switch to give the output side 12 volts and nothing still happens. I would replace the starter itself, but the light on the button is dim. I almost want to blame the control board, but don't know enough to condemn it. I'll do some checking in the morning. Just doing what I can before I turn it over to an RV shop.

DrewE

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Posted: 07/05/18 07:22pm Link  |  Quote  |  Print  |  Notify Moderator

txnese wrote:

The chassis engine fires right up, so that battery is good. I checked the house batteries with a volt meter and it reads about 12.6 volts. I also checked the generator's starter relay, got 12 volts on input side, and 0 on the output side. I push to start the generator and the output side shows like 4 volts. I was thinking bad starter solenoid, so I used a starter jumper switch to give the output side 12 volts and nothing still happens. I would replace the starter itself, but the light on the button is dim. I almost want to blame the control board, but don't know enough to condemn it. I'll do some checking in the morning. Just doing what I can before I turn it over to an RV shop.


The control board would not affect the voltage drop when the solenoid is engaged; the current for the starter does not go through the control board, but just from the battery positive (on one side of the solenoid), through the solenoid to the starter, and then to ground.

You have either a poor connection somewhere or a bad battery. Note that the generator often starts from the house battery, not the chassis battery, so the fact that the motorhome engine starts right up does not mean the battery supplying the generator is fully charged.

Assuming the house battery is charged, I would go over the wires to the battery, both the positive and ground ones, and the positive and ground connections at the generator. Something is almost certainly amiss there somewhere. The generator starter is a significant load (albeit of short duration), somewhere around 100A or so, and it doesn't take much of a poor connection to cause a significant voltage drop that would not be particularly noticeable for many other devices like lights etc.

I've seen a few battery cables that were corroded near the connectors inside the insulation, such that at first glance they looked okay when in actuality they were nearly or entirely open and just about falling apart.





Sam Spade

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Posted: 07/06/18 06:10am Link  |  Quote  |  Print  |  Notify Moderator

txnese wrote:

I push to start the generator and the output side shows like 4 volts.


Still assuming things that might not be true.

Do that again while measuring the input side of the solenoid.

The do it AGAIN while measuring the voltage at the battery.

Yes it is possible to drag the battery down to 6 V momentarily and then have it register 12 or more when the load is removed.

You STILL have not proved that the battery and connections are good.


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j-d

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Posted: 07/06/18 06:35am Link  |  Quote  |  Print  |  Notify Moderator

The odds are FAR GREATER that the ONAN is powered by the Coach/House Battery than by the Chassis/Engine Battery.
It's odd, but that little 4KY is VERY demanding on the House Battery. I've had the House battery seem good, find it didn't crank the ONAN. Replaced House Battery and all good including ONAN. Actually tested ONAN getting ready for a trip, found it wouldn't crank. Stopped at Walmart on the way to the campground and got a battery. Our coach has a single 12V Deep Cycle (trolling motor) House Battery.

Check all Battery Connections from House Battery to ONAN, including GROUNDS.

Try this: Put your meter across the House Battery and try to crank the ONAN. I think you'll find that "Load Test" will pull your House Battery Voltage down into Single Digits.


If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB

txnese

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Posted: 07/07/18 08:47am Link  |  Quote  |  Print  |  Notify Moderator

Battery was left to charge overnight. Tested fine with voltmeter, I also took it out to O'Reilly and have them tested the batteries. I have a voltmeter on the battery and voltage stays about 12v during starter. Tested on the input side of the starter solenoid and voltage is above 12v, this should show cable connection between battery terminal and solenoid is good. I tested the output side of the solenoid and get 12v with starter cable disconnected, with starter connected I get 8 volts. Bad starter? In the meantime, I'm double checking grounding cables.

* This post was edited 07/07/18 08:54am by txnese *

youracman

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Posted: 07/07/18 10:36am Link  |  Quote  |  Print  |  Notify Moderator

txnese- re: " I tested the output side of the solenoid and get 12v with starter cable disconnected, with starter connected I get 8 volts"

I assume you get the 8 volts while pressing the starter button. Please also let us know what voltage the other (power input) lug on the Onan starter solenoid reads while holding the start button down. If the 12 volts you measured at that lug was "open circuit" it does not guarantee you have a good copper path all the way to the battery; but a measurement under load tells a lot more.

Just data, FYI: My Onan service manual states that the minimum voltage allowable at the starter itself is 10 vdc. Of course "more is better"..... a lot better.

Also just some "real world" data: I actually pulled the plug wire and measured the starter current on my 4K Onan Microquiet a couple of years ago. It was 57 amps steady state. As DrewE mentioned, the inrush current is probably at least 100 amps.

Good luck with the fix.....keep us posted; we're all learnin'

ed s Currently: Denver, CO Formerly: Alvin, TX


Ed Sievers, Denver, CO
07 WGO Outlook 31-C; '16 Kia Soul with 6spd DIY Tranny
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txnese

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Posted: 07/07/18 01:32pm Link  |  Quote  |  Print  |  Notify Moderator

When I removed the cable from the solenoid to the starter, I get 12 volts on both sides of the solenoid with the start button pushed. when I reconnect the cable to the starter, input side has 12 volts, output side has 8 volts. So either starter is bad and drawing too many amps or solenoid is bad.

I've ordered a solenoid and it should be here Monday. Will keep everyone posted.

* This post was edited 07/07/18 01:38pm by txnese *

youracman

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Posted: 07/07/18 02:01pm Link  |  Quote  |  Print  |  Notify Moderator

Yup.........your diagnosis sounds "right on". Really hope it turns out to be a bad solenoid. I had to drop the whole unit on mine to replace a bad/weak magneto..........not fun, but doable. Whole thing weighs about 175 lbs.

Look fwd to your "got it fixed" post.

Sam Spade

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Posted: 07/08/18 06:51am Link  |  Quote  |  Print  |  Notify Moderator

txnese wrote:

I have a voltmeter on the battery and voltage stays about 12v during starter.


If that really means "during the time the starter is trying to run", then it indicates that there is a bad connection between the battery and starter. That might include the contacts in the solenoid.

The voltage at the starter should be within a couple of tenths of what it is at the battery.

Sam Spade

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Posted: 07/08/18 06:54am Link  |  Quote  |  Print  |  Notify Moderator

txnese wrote:

when I reconnect the cable to the starter, input side has 12 volts, output side has 8 volts. So either starter is bad and drawing too many amps or solenoid is bad.


IF....both of those measurements were made with the start button pushed, then the contacts in the solenoid are burnt. When the solenoid is closed, the voltage should be the same on both sides.....regardless of whatever else is happening.

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