Ran genset, now seeing 19+ volts from solar

[Snowman9000]

My MH has been sitting in the driveway for several weeks with the solar panels keeping it charged. NO shore power. Today I went in to run the genset.

The voltage meter read 13.6v before I did anything. The battery switch was On. No appliances or systems were turned on, it was on minimal life support.

I started the genset. After a minute or so I started the AC. After another minute or two the genset shut down. It was blinking 29, which means battery voltage over 19v. Which I thought was silly. I tried to restart it a couple of times but it shut down immediately and blinked 29. I putzed around and scratched my head for a bit.
Note: While the genset was running, I thought there was a relay chattering at the genset. That has been a recurring random issue.

Then I glanced over at the voltmeter and it was reading 19.6! I immediately tripped the circuit breaker coming from the solar panels into the Morningstar SS-20 controller, and the voltmeter went blank, telling me there was no longer ANY voltage in the house.

I checked my 100A fuse at the positive post of the battery bank and sure enough, it was blown. The battery bank read 13.2v at that moment, with the house cables disconnected. That's where things stand now. Let's set aside questions of what collateral damage there might be to boards and stuff.

It sure seems to me that the controller was letting the 19.6v go right through it. Or am I jumping the gun on that? How could running the genset (and therefore the converter) have damaged the controller?

What would blow the 100A fuse? It does serve the genset starter cable as well as the house. The genset cranking amps are 70-something. The fuse is a good one, a MRBF like this:



Put it another way, is there anything other than cranking the genset which could have blown the fuse?

My plan to start troubleshooting will be to disconnect everything from the batteries except the controller, then reconnect the panels and see what kind of voltage there is. And go on from there.

Thoughts?

Here is how I've got it wired. Obviously this is not a professional schematic. 🙂

[Snowman9000]

jrnymn7 wrote:
Yes, that was my concern... using the chassis to complete the neg pathway. Seems kinda odd to me.

It's pretty common.

[jrnymn7]

Yes, that was my concern... using the chassis to complete the neg pathway. Seems kinda odd to me.

[Snowman9000]

I see the source of your confusion now. The terminal up by the shunt is a stud on the chassis, which Forest River used for the same purpose. I just added connections to it. And the panel is also using the chassis for its negative connection. So the panel is definitely in the circuit.

[jrnymn7]

O.K., I see that now. The neg goes down to what looks like a chip bag clip, and then to the PD converter, but then it stops there. It is the pos side of the PD converter that continues to the panel, while the neg goes to ground. So it still may be a case of the 19.6v not getting to the panel.

[Snowman9000]

I am sure I have confused some of you by the timeline of genset starts, restarts etc. I am confused myself, so sorry about that. I do know this: It was flashing the high voltage error code when it shut down, and I was able to get it restarted more than once in that condition. Which would suggest that the fuse was blown, yet it restarted!

HOWEVER, the chassis-house interconnect might have been energized by what its black box read as having charging available for the chassis battery from the house side. It saw voltage greater than X (I'm guessing X = 13.0 or so) and its logic probably says "if V>13.0, close the solenoid and divert some charging current to chassis battery". There would have been enough volts and current from the solar controller to close the solenoid. Then the chassis battery would have been tied in to the house side, allowing the genset to do restarts/attempted restarts.

That is my theory about why I could continue to run the genset starter after the fuse blew. It sort of wraps up all the loose ends except for why the fuse blew. I'd like to say it was just the draw of the cranking, but why did the genset run for a few minutes, then sense 19.6v and shut down? We may never know, as I plan to put a larger fuse on and go from there.

[Snowman9000]

ewarnerusa wrote:

MrWizard wrote:
...i think the solar connection to the batteries belongs on the other side of that fuse,
move the solar connection or the generator connection
so that either fuse doesn't blow or solar is always connected...

Sorry to thread jack, but I hadn't considered this before but it makes sense. My solar controller is currently wired like the OP where the controller connection at the battery is on the protected side of my catastrophic failure fuse. It made sense to me at the time for EVERYTHING to be on the protected side, but I guess not?. Does a DC circuit breaker care about the direction of current to do its job?

It's my understanding that the direction does not matter to a circuit breaker.

[Snowman9000]

Drew,
No, the genset is definitely wired to the house battery. It did not start once the fuse blew. At the tail end of all this, the genset would not start. However its switch was still making it appear to me that it was available, this would be due to the juice coming from the solar. I did not fully describe that portion of the situation.

The terminals are all squeaky clean and tight, they all are like new.

I chose the fuse size myself. It is something I added that was not there from the factory. I do understand that it is supposed to be sized to the cables. I can't figure out what made it blow, and that bothers me.

Jrnymn: The solar is fed into the wiring prior to the fuse and battery. When the fuse blew, everything except the battery was able to get current and voltage from the solar.

I am not using the Load terminals on the controller. Just the terminals for the panels and battery. As to the negative path, everything is connected on the negative side before the batteries too.

[ewarnerusa]

MrWizard wrote:
...i think the solar connection to the batteries belongs on the other side of that fuse,
move the solar connection or the generator connection
so that either fuse doesn't blow or solar is always connected...

Sorry to thread jack, but I hadn't considered this before but it makes sense. My solar controller is currently wired like the OP where the controller connection at the battery is on the protected side of my catastrophic failure fuse. It made sense to me at the time for EVERYTHING to be on the protected side, but I guess not?. Does a DC circuit breaker care about the direction of current to do its job?

[jrnymn7]

Snowman said,

"Now, when the 100A fuse blew and the controller went to 19.6v, that voltage was being sent everywhere else."

I don't understand how 19.6v could be distributed throughout, without damaging anything?

It appears the "solar circuit" is limited to the panels, controller, and batteries. The 100a fuse blowing opened this circuit, thus stopping all power flow from the panels.

There appears to be no negative pathway to create another circuit thru the 12v distribution panel. This would be achieved by connecting to the "load" output terminals of the controller, correct?

[DrewE]

So the genset starts with the fuse blown? It must be wired to the chassis battery, not the house battery.

Don't replace the fuse with a higher capacity one without first verifying that the wiring and other components beyond the fuse can safely handle the higher current. The fuse is a safety device; putting in an oversized one defeats much of that.

The fuse may have blown not because more than 100A was flowing through it but because of e.g. aging or somewhat poor connections at the fuse causing extra heating.

[Snowman9000]

OK, everything checks out working fine, no damage to boards or anything I can think of to try.

I tried to run the genset but it was sucking air (1/8 tank). The chattering I was hearing was the fuel pump sucking air. I can't imagine that would blow the 100A fuse though.

I drove her into town, got gas, and now the genset is running well. Like I said, everything works, I'll just have to get a new bigger fuse. And a spare.

Don, I like a fuse for that catastrophic application.

[pianotuna]

Hi,

I'd consider a DC circuit breaker instead of the fuse. I would NOT use an auto reset one.

[red31]

@Voc, I=zero therefore watts = zero

[Snowman9000]

red31 wrote:
any watts at 19 v? 😉

You know, I panicked so quickly that I didn't read the watts.