Upgrading to LiFePO4 & 3500W inverter on 12V system. Please check this for issues!

[LifeStudent]

Upgrading a camper trailer Solar system. Attached wiring diagram for your review, please!!!

So, here’s a little info to help out with any answers y’all feel like supplying.
On a trailer camper, she has 3 Seraphim 305W 60-cell Mono panels.
She has …
Reliable 2500W 12V 120VAC Inverter (I’m concerned about the reliability of this brand, so open for suggestions).
Epever 80A 200V (though I suspect the paperwork is wrong and it’s actually a 150V) Charge Controller. Model: Tracer8420AN
She started with 4 golf cart batteries and had trouble running her microwave at full power.
She has now purchased 3 Li Time 12V 200Ah LiFePO4 batteries with a 100A BMS to replace the others.

She’d like to be able to run the microwave at full power, and she’d like to be able to use her air conditioner on solar (and past sundown occasionally). Those are the only power hogs that will be used. I’ve added pics of those two appliances for reference. A soft-start is being installed on the AC unit as well.

On the wiring diagram, there are some dotted lines that depict how something WAS wired on the old system. They also indicate areas that need clarification before the wiring diagram can be complete. For the purposes of this safety check, those can be ignored.

Thank you for any helpful input!!

 

[Tomthumb62]

Needs more batteries or a smaller inverter.

3500w/12.8v/0.85 inverter efficiency = 321 amps. Which would likely trip the BMS on one or more of the batteries.

 

[Tomthumb62]

Without doing maths, I’d say 3500W inverter is probably enough, using a soft start device on the A/C, to run the microwave and have the A/C start up at the same time. But I’m not sure about it, so I’d ask someone better with the math.

In any case, I don’t think you’d be able to go with a smaller inverter, so either get a fourth battery or convert to a 24v or 48v. IMO, anything over 200A is pushing it, or maybe it just scares me. 48V can be scary, too. But fora 12v system you’d need 4/0 AWG cable at least if not bigger, depending upon the length needed.

 

[LifeStudent]

Without doing maths, I’d say 3500W inverter is probably enough, using a soft start device on the A/C, to run the microwave and have the A/C start up at the same time. But I’m not sure about it, so I’d ask someone better with the math.

In any case, I don’t think you’d be able to go with a smaller inverter, so either get a fourth battery or convert to a 24v or 48v. IMO, anything over 200A is pushing it, or maybe it just scares me. 48V can be scary, too. But fora 12v system you’d need 4/0 AWG cable at least if not bigger, depending upon the length needed.

Thanks. Already checked the math on the cable size, so good to go there. Definitely using 4/0 cable… and paying special attention to make sure the connectors and connections are done right. 24V may be in the future, but not right now.

 

[LifeStudent]

Needs more batteries or a smaller inverter.

3500w/12.8v/0.85 inverter efficiency = 321 amps. Which would likely trip the BMS on one or more of the batteries.

Actually wondered if a 3000W Inverter would be enough. The inverter she purchased has bad reviews, and when I opened it up I found eight 40A fuses inside! Two were looking wonky! Any suggested brands? Thanks!

 

[Tomthumb62]

Actually wondered if a 3000W Inverter would be enough. The inverter she purchased has bad reviews, and when I opened it up I found eight 40A fuses inside! Two were looking wonky! Any suggested brands? Thanks!

Yikes that sounds sketchy.

Sorry I can’t recommend any thing specific as I’m only familiar with inverters 2000W and lower. I do love our newest 1000W Victron.

Are you able to measure inrush current with a clamp meter for the microwave and A/C? Or measure Power Factor with a kill-a-watt device? I don’t own a microwave but I’ve read that they can be brutal on inverters. And maybe she could get by with a smaller 600-700W microwave. Perhaps those measurements could help you better estimate size of inverter.

 

[LifeStudent]

Yikes that sounds sketchy.

Sorry I can’t recommend any thing specific as I’m only familiar with inverters 2000W and lower. I do love our newest 1000W Victron.

Are you able to measure inrush current with a clamp meter for the microwave and A/C? Or measure Power Factor with a kill-a-watt device? I don’t own a microwave but I’ve read that they can be brutal on inverters. And maybe she could get by with a smaller 600-700W microwave. Perhaps those measurements could help you better estimate size of inverter.

Unfortunately, can’t get power in to measure things, so just going off specs given. The microwave won’t be used but for 5-10 minutes at a time (and she’s already had to use it at half power before this upgrade, so she could always default to that if needed).

My concern is that she has what she needs for the AC (the main reason for the upgrade). Will an additional battery really make the difference? I actually have another post regarding this part that has the math computations …

Confused about inverter sizing as it relates to panels and batteries

My friend was told that she needed to upgrade her 2500W inverter to a 3500W inverter just because she’s upgrading her batteries, and someone else said it had to do with her solar panels. I have watched a lot of Will’s videos, and surfed this forum and other resources (but I’m not saying I know...

diysolarforum.com

 

[Texas-Mark]

Needs more batteries or a smaller inverter.

3500w/12.8v/0.85 inverter efficiency = 321 amps. Which would likely trip the BMS on one or more of the batteries.

The microwave only draws 1300W. Makes no sense to go smaller on the inverter, just don't max it out. A larger inverter won't have to work as hard. The 3 batteries should be fine as long as there is not something like an AC kicking on while the microwave is on. And even then the BMS surge is usually higher than the rated output.

 

[LifeStudent]

The microwave only draws 1300W. Makes no sense to go smaller on the inverter, just don't max it out. A larger inverter won't have to work as hard. The 3 batteries should be fine as long as there is not something like an AC kicking on while the microwave is on. And even then the BMS surge is usually higher than the rated output.

The BMS surge is 280, so that is correct. The AC and microwave at the same time can be avoided.

 

[Tomthumb62]

My concern is that she has what she needs for the AC (the main reason for the upgrade). Will an additional battery really make the difference? I actually have another post regarding this part that has the math computations …

Maybe the soft start device will be enough. But I can’t read the specs on that A/C unit to make sense of the math. Sorry, maybe someone else can. But 3x100A BMS is not a good match with a 3500W 12v inverter that can easily pull well over 300A. You do not want to trip the BMS and repeated doing so can damage the BMS, leading to battery replacement unless you want to cut open the case and try to replace it yourself. So either a smaller inverter, 24V system or a fourth battery.

 

[Texas-Mark]

But 3x100A BMS is not a good match with a 3500W 12v inverter that can easily pull well over 300A.

Still not seeing your logic. I have exactly that configuration in my cargo trailer conversion and it works fine. Starts a 5K BTU AC without even a hiccup, and I was just using a 1500W heat gun (for a few minutes) at the same time with no issues. Nobody says you have to max out an inverter's rated output, and it's not going to magically draw any more current from the batteries than the load you put on it.

 

[FLD]

We have a 3000/9000 SunGoldPower low frequency inverter-charger and a 500 amp-hour lifepo4 battery bank of one 300ah battery (200 amp bms) and two 100ah batteries (each has a100 amp bms). Our rooftop AC is a Coleman Mach with a soft-start.
The inverter-charger pulls 130 amps from the battery bank when the rooftop AC starts and runs. The camper's 12-volt devices consume up to 10 amps intermittently.
If the AC were to run continuously, the fully charged batteries should hit the low voltage disconnect in about 3.5 hours. With a more reasonable AC 50% duty cycle, we might get 7 hours of run time before low voltage disconnect
We've never tried using the microwave when the AC is on but I can do it this afternoon.
I'm planning to add another 300ah battery, for a total of 800 amp hours.
Edit: I just used the microwave while the AC was running. The amp draw topped at 246 amps. I kind of expected the 300ah battery’s 200 amp BMS to disconnect but it hung there for the 30 seconds the microwave was heating a cup of coffee.
Hopefully this helps.
On a sunny day our 600-watt solar panel setup can generate up to 50 amps. On an overcast day like today, they only generate 10-12 amps.

 

[Tomthumb62]

Nobody says you have to max out an inverter's rated output, and it's not going to magically draw any more current from the batteries than the load you put on it.

You're totally correct. However, it's always a risk and unnecessarily dangerous. If you have an inverter than can pull more amps than your BMS or fuse or wiring can handle, but you don't intend to use it, you'll always be wondering if you're getting too close to going over an edge. Plus cycling the BMS/fuse/wiring/etc to get hot and cool down can lead, over time, to corrosion/oxidation and then it's a downhill road from there.

If you have an inverter that simply cannot overtax any part of your system, you never have to worry about nor do you ever need to train your guests or house mates to NOT turn on too many things at once. And they will probably no even less than you do as to how much is 'too much'.

 

[Texas-Mark]

However, it's always a risk and unnecessarily dangerous. If you have an inverter than can pull more amps than your BMS or fuse or wiring can handle, but you don't intend to use it, you'll always be wondering if you're getting too close to going over an edge.

Sorry, but I have to disagree again. What risk? What danger? How hard is it too just stay within the confines of the limits? Put an appropriate size fuse/breaker in the battery cable for the max desired load if that paranoid. Shunts/current meters are cheap. Who does not have one? By your logic the grid is risky and unnecessarily dangerous because it is over-sized for a house. But wait... that's what circuit breakers are for, and using common sense on how much one can safely run without tripping breakers or the mains.

Putting in a smaller inverter solves nothing, and IMO just creates problems. As I mentioned, a larger inverter does not have to work as hard as one that is pushing it's limits. That's one of the reasons I went with a large one. I don't believe it is over-sized. I just don't plan to come close to maxing it out for more than a few seconds, if ever.

 

[Tomthumb62]

By your logic the grid is risky and unnecessarily dangerous because it is over-sized for a house.

You're comparing apples to oranges. In a appropriately sized house electrical system, all fuses/breakers and wires will be sized properly. A breaker should not ever trip and if it does, it should be a rare occasion, not a daily thing. In the case we're both referring to here, the person was trying to put a 328A load (in theory if maxing the inverter out) on 3x100A BMS. Unless it's top tier BMS, it's risky (not paranoid) to not only run three BMS at full capacity, but 9.3A overcurrent for each of the three BMS. You could put a 250A breaker on that load, but it's hard to know in this situation that that wouldn't simply be tripping all the time because their A/C and microwave would be drawing too much current. I think they need either a 24v system or a fourth battery for the possibility of 400A loads.

I'm talking about a specific example here. You seem to be taking my words out of context and extrapolating them to generalities.

 

[Texas-Mark]

You're comparing apples to oranges. In a appropriately sized house electrical system, all fuses/breakers and wires will be sized properly.

In a properly wired and fused system, and knowing your loads, it does not matter how big the inverter is. It will only supply what is asked of it.

In the case we're both referring to here, the person was trying to put a 328A load (in theory if maxing the inverter out) on 3x100A BMS.

You keep thinking that people are going to max out the inverter. Why? If they know the draw of devices, it's a non issue. I don't max mine out because I know what my AC draws and I know my other loads. Firing up that heat gun simply proved it could handle 1500 more watts than I normally use.

You could put a 250A breaker on that load, but it's hard to know in this situation that that wouldn't simply be tripping all the time because their A/C and microwave would be drawing too much current.

IF it's tripping all the time, then yes, a bigger battery bank is needed, not a smaller inverter. But for the AC, the biggest draw will be on startup and a big inverter (LF) will absorb most of that without much effect on the BMS. The OPer already said the BMSs have a healthy surge capability.

In any case, IMO it would be easier to add another battery IF needed, than needing to get a bigger bigger inverter AND still needing another battery.

 

[LifeStudent]

Edit: I just used the microwave while the AC was running. The amp draw topped at 246 amps. I kind of expected the 300ah battery’s 200 amp BMS to disconnect but it hung there for the 30 seconds the microwave was heating a cup of coffee.
Hopefully this helps.

Thanks for the update! Does help.

 

[FLD]

I understand both sides of the conversation.
In our case, a low frequency 2000/4000 watt inverter-charger would have worked just fine for our camper. The only reason I bought the 3000/9000 inverter-charger was because it can charge at up to 85 amps whereas the 2000/4000 charges at up to 45 amps. I wanted the higher charging capability.
This inverter typically runs at 50-55% of it’s continuous rating when the rooftop AC is running so the smaller one would have worked fine.

 

[Mia]

Sorry, but I have to disagree again. What risk? What danger? How hard is it too just stay within the confines of the limits? Put an appropriate size fuse/breaker in the battery cable for the max desired load if that paranoid. Shunts/current meters are cheap. Who does not have one? By your logic the grid is risky and unnecessarily dangerous because it is over-sized for a house. But wait... that's what circuit breakers are for, and using common sense on how much one can safely run without tripping breakers or the mains.

Putting in a smaller inverter solves nothing, and IMO just creates problems. As I mentioned, a larger inverter does not have to work as hard as one that is pushing it's limits. That's one of the reasons I went with a large one. I don't believe it is over-sized. I just don't plan to come close to maxing it out for more than a few seconds, if ever.

I’m far from a professional and just adding a thought here…. ie) But it’s not necessarily a house setup which would typically lean towards closer to a 48v setup than a 12v setup, and as such the wiring would be better able to handle the physical science side of things as a result; and not for nothing, but there’s a lot of bouncing and movement going on in a camping trailer then a house- and things can/will get loose and possibly scraped up over time more frequently as a result, so even with the best of plans, it may not play out in theory; and secondly I personally wouldn’t feel safe knowingly setting it up so that it could be close to being maxed out, exactly because of the fact that I’m still learning and not yet fully obtained a confident enough handle on the actual repercussions of such possible concerning issues of such a system.

My initial 12v experience was just using it to run the lights and a 3 way fridge on the dc option occasionally to help conserve propane while camping . Now we’ve moved up to semi-gl’amping it and want to use it to run our household appliances while we are not hooked up to shore power (such as coffeemaker, the microwave, to charge up and run our electronic devices)… Such as with running the fridge off of AC so that it will switch over to LP automatically in the case of a failure as much as possible while in transit to save on the use and cost of propane, since we have ”prepaid” and hence now have a degree of free power being generated from our 40 amp SCC and the 40 amp dcdc charger… and hence have enough power being produced while driving to keep the batteries charged up… so our plan now is to use the inverter to take advantage of the lifepo4 storage battery bank in order to use such appliances as the microwave for a few minutes to heat up some food for lunch or make a pot of coffee, etc. and other than that mostly it would just be used to run the fridge and e-devices or led lights, water pump , UV water treatment as needed.

Also, has anyone experienced better results running their 3 way fridge off an inverter while in transit than the 12v directly? The couple of times we’ve tried using the ac (power not air conditioning) option on the way home on a travel day to see how it would do, it actually seemed to keep the temps up better than our previous attempts when it was run solely on dc, which seems counterintuitive to me. I’ll obviously need to continue to research it more scientifically this winter season (as fingers crossed) we will be doing some snowbird traveling without hookups finally (and really test out the complete power system which consists of a 520 aHr lifepo4 battery bank, 400 watts of solar, the 40 amp Epever SCC along with a 3000 watt Renogy inverter; hence gl’amping it up in an Arctic Fox 990 truck camper, lol!)

 

[Texas-Mark]

I personally wouldn’t feel safe knowingly setting it up so that it could be close to being maxed out,

Seems like some of you are still missing the point. The only way anything gets maxed out is if you put too big of a load on it, and max it out. It's like having a 550hp engine in your car. It's not going to magically go 120mph and 10K rpm unless you push on the accelerator.

As I said, I've been running a 12V 3500W inverter forever, and yet no loads that I have not put on it, magically appear. It runs 24/7 happy as can be at about half it't rated output. But if I do need to max it out short term, it still works just fine. And if something did short out (which could happen regardless of inverter size), that is what fuses and a BMS are for.