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Old 05-15-2022, 08:39 PM   #1
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Problems with new Victron Multiplus

Need some help y’all.

We just added a Victron multiplus 12/3000 onto our Winnebago vista 31ke. Also switched the batteries to golf cart batteries running in parallel. We had a shop do the install. We are having some issues over the weekend and taking it back to the shop. What are y’all’s thoughts on this situation and are there any specifics I need to direct the shop to look at and resolve?

On our Vista, the generator has to be plugged in to the 30A shore power input in order to power the RV. There is not a transfer switch.

After the inverter install we brought it home. Then started the generator, then turned on the HVAC. The shop had not plugged back in the generator cable into the 30A input when they unplug their shore power. So immediately the HVAC was trying to pull through the inverter straight from the battery, went for about 10 minutes before we heard the alarm, realized what happened and shut it off. We had the burned plastic/fishy smell.

I took it back to the shop, they checked it out and confirmed we didn’t harm the unit, just “ran the hell out of it”. We are installing a soft start on the HVAC to go easier on the generator and a transfer switch this week.

After I brought it back home Friday I started testing stuff. We ran 2 fans and a TV off the batteries. No issues. Then started the generator and let it run to charge the battery. In the compartment where the inverter is the I noticed it seemed a little hot and that smell was subtly back. Then I noticed the power cable that connects to the batteries looked like melted plastic on the cable connection.

So today I decided to get deeper on testing. I slowly added electronics every 15 min. I got up to pulling 215 W AC load with no problems. The temp (using a laser thermometer) was between 84-86 degrees F the whole time.

Then I ran the microwave for 1 minute. The wattage was pulling about 1250W. The temp at that cable jumped to 95 degrees F. Only time I saw it jump while pulling power.

After that I shut off all the devices inside and let it sit for 10 min. Then turned the generator back on and ran it for 10 min, then plugged it in to let it charge the batteries. The inverter switched over to bulk to start charging. Everything looked good.

Came back out to check on it after 30 minutes and the cable connection was at 230 degrees F. The red cable was sticky to the touch. The inverter itself and connections on the inverter were fine, 84 degrees. 86 at the fan. But the connection that went to the battery was dangerous hot. So Atleast I found what was melting the plastic ands causing the smell.

So long story short,

I am taking it back to the shop this week to resolve. I am planning to have them re-check everything on the current set up to see what is causing this issue before doing the transfer switch and soft start. Is there anything specific I should also have them check out?

We leave for a 6.5 week trip on 5/27 and trying to make sure everything is set up and safe!!!
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Old 05-15-2022, 09:11 PM   #2
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Unless the golf cart batteries are 12v dc they should not be in parallel.
More than likely they are 6v dc batteries and a pair should be connected in series to provide a 12v dc source of power.
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Old 05-15-2022, 09:59 PM   #3
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You are correct, they are in series doing exactly what you stated. This is why I don’t do my electrical work.
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Old 05-15-2022, 10:01 PM   #4
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How many GC batteries do you have?

What size cables are between the batteries and the MultiPlus? Distance between them is a factor too.

When set up, the MP can be set to turn off when the battery voltage get too low. Ask the shop what they set it to.

What's the purpose of adding the Soft Start? Without a lot of batteries, you'll not be running the HVAC off the inverter. But it might be easier on a smaller gas generator.
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Old 05-16-2022, 06:19 AM   #5
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highly likely the shop that installed this system undersized the cables between the inverter and the batteries as well as the cables between the batteries.

They should have use 4/0 cables......when you speak with them this is NOT the same as 4GA cables...... a 4/0 cable is about as big around as your index finger and especially with that 3000W inverter running a 12V battery bank it will easily overheat smaller cables, which is what it sounds like from your description. Try using a simple infra-red temp gauge on each of the battery lugs in the compartment you describe smelling overheating and you'll be surprised at how warm they are getting if the wire size is too small.

I'm sure others will tell you that this size cable is not needed for such a small system......NOT!!

Good luck
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Old 05-16-2022, 06:40 AM   #6
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highly likely the shop that installed this system undersized the cables between the inverter and the batteries as well as the cables between the batteries.

They should have use 4/0 cables......when you speak with them this is NOT the same as 4GA cables...... a 4/0 cable is about as big around as your index finger and especially with that 3000W inverter running a 12V battery bank it will easily overheat smaller cables, which is what it sounds like from your description. Try using a simple infra-red temp gauge on each of the battery lugs in the compartmentyou describe smelling overheating and you'll be surprised at how warm they are getting if the wire size is too small.

I'm sure others will tell you that this size cable is not needed for such a smallsystem......NOT!!

Good luck
Here are some pictures of the wire in question. I think it is the right size wiring. These are big wires, about the size of my index finger.



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Old 05-16-2022, 06:44 AM   #7
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The wire size should be printed on them.

Definitely seems like a wire has been overloaded trying to run the a/c unit.
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Old 05-16-2022, 06:47 AM   #8
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hard to tell from your picture, but is that Blue Sea T fuse holder melted? Some of the black plastic under the red cable looks damaged.
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Old 05-16-2022, 07:00 AM   #9
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hard to tell from your picture, but is that Blue Sea T fuse holder melted? Some of the black plastic under the red cable looks damaged.
100% it is.

My theory….

When we accidentally ran the HVAC for 10 minutes and had that initial issue it overloaded that cable and melted the fuse holder messing up the connection.

So then when I simply ran the generator to charge the batteries later it is causing the continued overheating of that cable. And continuing the overheat where the fuse holder was damaged causing the subtle smell versus the strong smell with the HVAC.

We do not want to run the HVAC on the battery. Not enough power for that. That was an accident, but I think that 10 minutes of accident jacked up that cable.

Other than that the inverter itself seems to be doing exactly what it is designed to do, correctly.

Does that hypothesis sound right? Are there some other Areas we should dig into to make sure we are safe?
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Old 05-16-2022, 07:32 AM   #10
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How many GC batteries do you have?

What size cables are between the batteries and the MultiPlus? Distance between them is a factor too.

When set up, the MP can be set to turn off when the battery voltage get too low. Ask the shop what they set it to.

What's the purpose of adding the Soft Start? Without a lot of batteries, you'll not be running the HVAC off the inverter. But it might be easier on a smaller gas generator.
2 GC batteries running in a series. The purpose of the soft start was to lower the wattage coming in at the startup on the HVAC. We only have a Onan 4000 as our generator. And the AC pulls over 3k watts on the startup and then settles around 1500W. The thought was to not push or peak anything on start up.
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Old 05-16-2022, 08:49 AM   #11
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100% it is.

My theory….

When we accidentally ran the HVAC for 10 minutes and had that initial issue it overloaded that cable and melted the fuse holder messing up the connection.

So then when I simply ran the generator to charge the batteries later it is causing the continued overheating of that cable. And continuing the overheat where the fuse holder was damaged causing the subtle smell versus the strong smell with the HVAC.

We do not want to run the HVAC on the battery. Not enough power for that. That was an accident, but I think that 10 minutes of accident jacked up that cable.

Other than that the inverter itself seems to be doing exactly what it is designed to do, correctly.

Does that hypothesis sound right? Are there some other Areas we should dig into to make sure we are safe?
When you go back to the shop, you might want to have a conversation with them about hooking up your HVAC to the AC#2 outlet on the MultiPlus, at least understand your options. This will not allow the air condition to do what it did (inverter running the roof a/c.)

I don't know how you're set up, it may require a new wire routed from the MP up to your air conditioner circuit breaker, possibly even setting a separate sub panel for the HVAC only.
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Old 05-16-2022, 07:43 PM   #12
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3000k Multiplus should be able to run an AC but not with just a pair 2GC batts. Also should be able to provide boost to run it in hybrid/load share mode. Once AC compressor started ,should been pulling about 12A @ 120v so only 120A 12v.
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Old 05-17-2022, 04:32 AM   #13
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3000k Multiplus should be able to run an AC but not with just a pair 2GC batts. Also should be able to provide boost to run it in hybrid/load share mode. Once AC compressor started ,should been pulling about 12A @ 120v so only 120A 12v.
The boost part for sure - we've used our many times to add a bit of current when plugged into a 30-amp pedestal. Amazing to see how seamlessly it can go from charging the batteries to helping the shore power start up an a/c unit, and then switch back to charging.

But, the problem I've seen with trying to run a large load such as a microwave is the discharge profile of the lead acid batteries. The voltage drops pretty quickly with them under heavy load, so even another pair of AGM might not provide much a/c run time.

It's not that they don't have the ability to go longer, it's that they don't have the ability to maintain constant voltage under heavy load. If we didn't sell the coach, the plan was to upgrade to lithium batteries. They do much better holding voltage under load and should perform better powering something like a microwave, a/c unit, etc.
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Old 05-18-2022, 06:45 AM   #14
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UPDATE

Thanks for all the feedback everybody. Looks like we have it resolved.

We upgraded the wiring to 4/0. The manufacturer recommends 2/0, but after hearing y’all and trouble shooting with my tech we learned that 4/0 was the only route to go.

After that we added the smart start to the HVAC.

Last, we did some programming on the inverter to focus more power to the AC Lead when running something heavy like HVAC or microwave instead of trying to split equal between charging battery and running power.

Made these changes and this thing runs like a dang champ. We pushed the limits hard on it yesterday to test and it is a beast.

We are set up to hit the road next week and are a step ahead on transitioning to full solar next year.

Thanks again!
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