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. 🙂

[red31]

any watts at 19 v? 😉

[Snowman9000]

I'm back. I'll try to comment without going back and quoting all the various things I want to remember to comment on. 🙂

First, Mr Wizard, I agree that the solar controller to the battery needs to be after the 100A fuse. That was a big mistake, as we now see.

Question: where was the voltage reading taken? Answer: Point A. Before the battery fuse, after the controller. Tied in with everything.

Now, when the 100A fuse blew and the controller went to 19.6v, that voltage was being sent everywhere else. To the inverter (which has internal protection), to the genset controls, to the fuse panel and everywhere beyond, and possibly even to the chassis battery, depending on the logic of the little system that controls the interconnection relay. Oh, even that thing too got hit with 19.6v. If nothing blew, I'll be really lucky.

I'm having a hard time accepting that the 100A fuse blew just as the genset started. I mean, sure it could have done that. I know that the 19.6v had nothing to do with the fuse blowing. But, the genset ran for several minutes, then shut down with the error code. It seems likely that was the moment the fuse blew. But why? I wonder about what I think was a chattering relay at the genset. With all the genset noise and rattles, it was hard to say. In fact I had removed the cover on the genset was trying to pinpoint the noise when the genset shut down. Maybe it's the starter relay, and it caused the fuse to blow. I wish I knew how to troubleshoot it. It obviously works when it's time to start the genset.

BFL: As jrnymn said, I saw the 19.6v after it had been present for a few moments, THEN disconnected the panels.

ALL: Any recommendation on the size of the replacement fuse? This is all pretty new installation, and I decided on the 100A. Well, I DID use my clamp on ammeter and measured 70-some cranking amps, and that's when I decided on 100A. It's supposed to be a catastrophic fuse. Size wise, it is protecting 2 gauge cabling. It sure seems like it needs to be bigger, like 125 or 150?

[jrnymn7]

BFL,

He saw the 19.6v, and then opened the panel-to-controller circuit. So for a few minutes there was panel power to the controller, with no connection to the batteries.

[BFL13]

jrnymn7 wrote:
Hmmm, that's a good point, PT.

Maybe the controller was not damaged, but simply passing thru Voc, due to no load?

I keep asking--howinheck can it pass through anything when the OP said he opened the panel to controller path with that circuit breaker??? There is no input to pass through.

[jrnymn7]

Morningstar SS 20 Manual

[scrubjaysnest]

The SS 20 is a PWM controller, with no battery(s) connected it will rise to Voc of the panels that is why you have a means to disconnect a CC input first. The CC output needs to be wired directly to the battery via it's own fuse or breaker as others have said.

Loose connections or corrosion between the battery and genset will cause it to draw more current when starting. This is most likely the fuse failure.

Do a step by step check. Wiring, connections etc. Replace the fuse. Check your 12 volts at the distribution panel. Everything ok. With the converter turned off and the CC disconnected from the battery(s); connect to shore power and turn the converter on. Everything ok. Turn the converter off and disconnect shore power. Start the genset; everything ok. Turn off the genset. Connect the CC; everything ok; now start the genset; everything ok. With the genset and the CC both on turn on the converter; everything ok.

[jrnymn7]

Hmmm, that's a good point, PT.

Maybe the controller was not damaged, but simply passing thru Voc, due to no load?

[pianotuna]

Hi snowman,

If there is the equivalent of "no battery (fuse blown)" then the controller does not know what voltage battery it is connected to. That is how they "decide" what voltage to output (12, 24, 36 etc.)

What controller is it?

It is prudent to connect the controller to the battery using a fuse that would protect that wire. Doing that through a 100 amp fuse essentially means the wire to the controller is unprotected.

Hopefully the control boards will not have let out the magic blue smoke.

[jrnymn7]

Actually, according to his schematic, even the 19.6v solar voltage could not have made it to the bank, seeing as it had to go thru that (blown) 100a fuse.

So, the gennie's starter blows the 100a fuse, just as the gennie starts up. This in turn disables all power, both in and out of the battery bank. The solar controller becomes inoperable, due to its being connected to the panels only, and thus stops bucking. And there's no other damage to the bank, or anything else... all due to that blown fuse.

[BFL13]

In the OP , he said he opened the breaker between the panels and controller. So he had the controller still connected to the batteries, which is correct.

He then noticed he had no voltage anywhere, which is correct since his solar was off and his genset had shut down, so no converter on.

What we don't know is what voltage the converter would do if only he had a 120v source to run it.

[jrnymn7]

Then doesn't it make sense that the 100a fuse blew moments after the genset fired up, causing the solar controller to be connected to the panel array only, thus damaging the solar controller, which in turn stopped regulating/bucking the voltage? And if so, I would not expect there to be any collateral damage, seeing as there would be no power from the batteries to the 12v distribution once the 100a fuse blew, and only the bank would see that 19.6 volts.

[westend]

jrnymn7 wrote:
"My other WAG is that something drew over 100 A of current from the battery."

Could the genset do that, initially, on start up?

What genset? If you have a starter on the genset with a loose connection or is failing, yes, it's possible.

[jrnymn7]

"My other WAG is that something drew over 100 A of current from the battery."

Could the genset do that, initially, on start up?

[MrWizard]

replace the fuse, clean those heavy connections including the genset cables
buy or borrow a clamp on DC amp meter and check the amps load when the generator is starting

i agree, i think the high reading is because the solar is disconnected from the batteries via the blown fuse

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

FYI
the panels are supposed to be disconnected before disconnecting the batteries
some controllers would be damaged by a fuse blowing and disconnecting from the batteries

[BFL13]

With the panel to controller path open, there was no more controller input and so no output. Your shunt measures solar output which was 13.6 before you started the genset.

Then you got 19 volts. Nothing to do with the solar. The genset started the converter, which has been dormant for ages.

Some converters have been reported to run up in voltage due to some sort of internal fault. To check the converter without involving the genset (which shuts off), unplug it from the rig's receptacle and run an extension cord to it from the house or some other 120v source. Now check the converter's output voltage.