AC Unit intermittent surge problem

[howson]

Okay, so interesting findings here. The refrigerator does share a circuit with other receptacles and the refrigerator was not the issue. It turns out to be an issue with a Brother printer. We have now tried two different printer with the same results. I've also moved the printer to a separate circuit from the refrigerator and same results. The Multiplus starts assisting when the printer is powered on, and then I get a battery low and overload alert. One time the Multiplus went into Fault, and I had to manually turn it off and back on. As part of the test, I turned on an instapot, portable heater, and AC unit, drawing 3300 w from the inverter on battery only, and got an overload, but no fault.

Anybody else had issues with Multiplus and a printer?

Wow--how much power is that printer pulling? Do you have a BMV to monitor the amps being pulled from the battery?

[ncitro]

JohnD Yeah laser printers have a huge inrush when they fire up. They charge the toner inside to bond it to the paper. As said above that's why you cannot run them on a UPS either. I would put it on a circuit that's not wired into your inverter. Otherwise, though I am generally against anyone ever using an ink jet, that may be your only option.

As a side note, what do you have for batteries? I'm not surprised the MultiPlus could not handle the load, but I'm surprised you're getting a battery low error. Usually that would mean it can't pull enough current from your batteries. If you're running lithium that shouldn't be an issue, but if you're on lead acid I'd say you don't have enough batteries to supply the current the inverter is looking for. Even if you didn't have the capacity to do it for any length of time, I'd think you should still have the voltage if that makes sense.

[JohnD]

ncitro I have 4 100AH Battle Born batteries. I just ran a test overnight where I had the heater set at 62 (not very cold night, dropped to about 40), the refrigerator, and the tank heaters running. The refrigerator was set on AC. It was at full battery around 9 PM, and ten hours later it was at 12%. I haven't done any calculations, but that seems too low.

[JohnD]

ncitro I should also note that the batteries are wired with 4/0 cable, roughly 5-6 feet cable length from negative battery terminal, via shunt, to Multiplus. Roughly 4-5 feet cable length between positive terminal, 400 amp ANL fuse, 300 amp ANL fuse, disconnect switch, and Multiplus.

There is plexiglas above the wiring, so try to ignore the reflection. Negative battery terminal from leftmost battery goes to shunt. I will also note that the temperature sensor from the Multiplus is attached to the rightmost negative battery terminal (it happened to be an oversight, and the left one was not accessible at that point). Also worth noting that I attached a 1/8" x 1" copper bar to the to top two studs of the 250 AMP negative bus bar to carry the additional current. I had tried connecting the negative from the Multiplus directly to the shunt, but the bolt length on the shunt seems marginally too short for two lugs. The 300 amp fuse is a little dicey, but I think it is fine. I just bolted it in between the provided mount and the switch. Had I moved the switch down lower, and attached with a copper bar, then I wouldn't be able to get the circuit board in to the space above the batteries with it pre-wired ( I need to tilt the board forward to get it in unless I detach all the positive terminals) As it stands, I need to attach the Solar Charger after the board is up for the same reason. I have very little space to work with and was running out of time. I will probably re-wire portions at a later date.

[howson]

JohnD -- see https://gdrvowners.com/forum/operati...r-not-accurate or for a longer read https://gdrvowners.com/forum/operati...laying-100-soc

[ncitro]

ncitro I have 4 100AH Battle Born batteries. I just ran a test overnight where I had the heater set at 62 (not very cold night, dropped to about 40), the refrigerator, and the tank heaters running. The refrigerator was set on AC. It was at full battery around 9 PM, and ten hours later it was at 12%. I haven't done any calculations, but that seems too low.

That does seem like a lot of draw, but at the same time, four BattleBorns should be enough to handle the surge from the Multiplus. The inrush from the laser must just be too much for the MultiPlus to handle.

[openrangeowners]

According to what some people are posting, running the RV Fridge on AC will draw 3 amps AC, about 30 amps DC (via the inverter) - so over 10 hours that would be 300 amp/hours or 75% of your capacity. My inverter draws somewhere between 4 and 5 amps DC (with a few things plugged in like microwave, 2 TVs, etc.) - granted the fridge will not run continuously, but you also had your furnace running, so that probably made up for things . Sounds about right - 88% usage.

[JohnD]

So, I was lucky to avoid a catastrophe. We were testing the plumbing in the RV today and it started to smell hot. I went out and checked and found the positive cables to the Multiplus to be very hot, especially between the 400 amp fuse and the 300 amp fuse. It turns out that the nut holding the 300 amp fuse was loose. Fixing that seemed to fix the low battery alert, but still throws an overload and battery voltage ripple alert with the printer.

It got hot enough to mildly scorch the mounting board above the 300 amp fuse. Scary!

[howson]

It got hot enough to mildly scorch the mounting board above the 300 amp fuse. Scary!

Yikes. Scary is right.

I'm still curious how many amps of DC power that printer is pulling through the inverter. You should be able to monitor on your BMV (since you have a shunt I assume you have one). But at this point it might be prudent to stop using the printer--period--when the Multiplus is inverting.

Oh--and switch the refrigerator over to propane when inverting (except--this is a controversial opinion--when towing). Your batteries will last a lot longer!

[JohnD]

Unfortunately, tightening that connection did not solve the problem. I am actually on the road now, so fixes will be a bit more difficult. I was running the electric hot water heater and a space heater, pulling 3600 watts according to the battery monitor. The same location heated up again. Too hot to touch. The 300 amp fuse looks like it was about to melt. Any ideas from the experts? Is there something wrong with the 300 amp fuse or the way it is mounted? I was planning to do a Harvest Host tonight on the way south, but won't be drawing any A/C from the Multiplus until this is fixed. I may have to find a campsite for hookup instead.

[howson]

Unfortunately, tightening that connection did not solve the problem. I am actually on the road now, so fixes will be a bit more difficult. I was running the electric hot water heater and a space heater, pulling 3600 watts according to the battery monitor. The same location heated up again. Too hot to touch. The 300 amp fuse looks like it was about to melt. Any ideas from the experts? Is there something wrong with the 300 amp fuse or the way it is mounted? I was planning to do a Harvest Host tonight on the way south, but won't be drawing any A/C from the Multiplus until this is fixed. I may have to find a campsite for hookup instead.

John,
Using 3600 watts means there was 300 amps of 12vDC coming from the batteries. Watts/voltage=amperage That's a very high load being pulled from the batteries--the inverter was in overload since 3600W/120vAC=30amps. The 12/3000 is meant to provide a maximum sustained 25A of 120vAC (or 3000 watts).

Bottom line: there may be nothing wrong with the setup.

Forgive the bluntness--but stop using the inverter with high amperage devices for a long duration.

My .02: when boondocking, run the water heater on propane. Do not run any form of electric heater of any type off the batteries for any length of time. The Multiplus is great for short-term use of high amperage devices (like the microwave) but not for the long term.

This advice also pertains to your RV refrigerator (assuming you do not have a residential). When boondocking, run the refrigerator on propane, not AC. You may have to manually select the propane mode.

I'm just an owner like you...but if you consult a licensed electrician or certified RV mechanic I am very sure you'll get the exact same advice. Hopefully the owners here who are (or were) electricians will back up what I've just written.

Howard

[ncitro]

JohnD Howard is exactly right. That's past the Multiplus max running capacity and well into it's surge capacity. I would expect the fuse to be hot lol. Having an inverter connected to all the circuits in the rig (which it sounds like you are) requires some manual power management on your part to prevent an overload. HWH and fridge on propane, and use your propane furnace for heat. Even if the Multiplus could keep that load up, at that draw your batteries would only last for a little over an hour (I think I remember you had for BattleBorns).

[openrangeowners]

I think I see what might be contributing to your heating issues - the contact area on the 300 amp fuse is under the bolt. Most fuse holders sandwich the fuse between two washers to provide a larger surface area on both sides for the power to go through. I would recommend adding a washer below and above both sides of the fuse (on the one that is visible, the terminal lug probably takes care of bottom part, but you have the bolt on the top without a larger washer between it and the fuse (at least from the picture it appears to be that way).

Upon further review, I do see you have a washer under the bolt and above the fuse end ... so probably disregard my comment ...

[openrangeowners]

Can you eliminate that connection by connecting the switch directly to the post instead of going through the 300amp fuse (one less connection to cause an issue)? I was told the 400amp fuse will be sufficient to protect the wiring and the inverter will shut off if overcurrent driven.

[JohnD]

Thanks for all the replies. I should probably add that I'm an electrical engineer (or was one about 30 years ago). I appreciate that I'm going to need to be selective about how I run things while boondocking, but I'm also trying to shake this thing down a bit and ensure everything is working properly. This morning, I was actually plugged in to a 15 amp circuit and trying to put a bit of heat into the RV because it was 25 degrees, and I was going to be driving in cold weather for a bit, all while saving some propane, because we are in short supply and boondocking tonight.

Personally, I'm not comfortable with a system where the consequences of mismanagement are fire vs throwing breakers. I suspect this fuse is not capable of handling this load. The other day when I was experiencing these problems, the negative (black) cables were ambient temp, but the red from the output of the 400 amp fuse through the switch were scorching hot. There is clearly too much resistance through this section. The fuse should blow before it starts a fire. I will have some time to troubleshoot in a couple of days and I will start with Mark's recommendation of skipping the 300 amp fuse and test it at high loads to see how hot it gets. Again, I intend to be careful about how I use the system in real life, but I can't always expect to be on my game, or expect the same of my wife and guests. I don't want the penalty to be fire.

Edit: Upon re-reading my post, I hope I didn't come across as arrogant or unappreciative. I'm not sure how I would reword it to ensure that is the case, so I'll just leave this comment. I appreciate all the input.