Leisure battery and inverter

[Frm2005]

Hi all, bit of a head scratcher here, hoping for some advice on this. Here’s my set up, I’ve got a VW caddy maxi van I have a leisure battery powering a 3000w pure sine wave inverter. I have a 25mm² cable coming for the live terminal of my vans battery through a split charge unit which switches on when the vans running, charging the leisure battery in the back. The negative is bolted to the frame of the van. However, when I try and use my microwave it drops voltage on the screen of the inverter alarms and shuts off. It does work a bit better if the vans running linking both the main battery and leisure battery, but it’s very temperamental. It worked perfectly in my old van however, this vans a little longer, could volt drop be an issue? I’ve tried putting two leisure batteries in parallel too, this hasn’t resolved the issue. It’s a cheap 800w microwave I’m using, not sure if I need to try and use a lower wattage unit see if that helps, or move the inverter and battery closer to the main battery of the van. What’s your thoughts? Any advice is much appreciat
ed.

 

[pappajohn]

That's 800watt output.... The input could be at least double that and initial startup even higher.
For a 3000w inverter you are going to need four 100ah batteries.
The battery isn't capable of supplying that current for long so it sees it as the battery is flat.
At 1600w input it's pulling 135amps from the battery and it isn't designed for that sort of current drain

 

[Frm2005]

That's 800watt output.... The input could be at least double that and initial startup even higher.
For a 3000w inverter you are going to need four 100ah batteries.
The battery isn't capable of supplying that current for long so it sees it as the battery is flat.
At 1600w input it's pulling 135amps from the battery and it isn't designed for that sort of current drain

Ok, what do I need? I basically want to warm some pre prepped food up in the back of my van. What would be your suggestion for this issue as my current set up isn't working.

 

[oldiesontour]

How long is the 25mm cable between the battery and inverter,how far apart are you s b and lb ? Do any of the wires or connections get warm.
Regardless of any of the above pulling that sort of current from a single la battery will very quickly kil it

 

[Frm2005]

How long is the 25mm cable between the battery and inverter,how far apart are you s b and lb ? Do any of the wires or connections get warm.
Regardless of any of the above pulling that sort of current from a single la battery will very quickly kil it

The main van battery is about 5m away from the leisure battery. The inverter is about 2m away from the leisure battery. I've seen online people using a microwave with no issues in their set up. What microwave would I need to work? As mentioned I've just bought a standard cheapo on line. Do they make one specific for this type of set up?

^{_{Subscribers  do not see these advertisements}}

 

[starquake]

Yeah, needs to be a lithium battery and you may need 3 for that kind of draw. Depends on the BMS rating in the Lithium battery.
You can't draw that kind of power from a lead acid battery, it (as you have discovered) can't deliver that amount of charge rating.

We run that kind of thing on an Ecoflow Delta2 in our van (an all in one Lithium battery and inverter, able to deliver 2000w sustained 2400w peak pure sine wave). These can deliver that kind of flow as the BMS in them is rated for that kind of draw. Even most Lithium batteries will be limited in peak flow to likely need 2 of them. You could do it yourself, but you'll need to pick the right Lithium battery and BMS to deliver that kind of flow to your 3000W inverter. I presume the 3000w inverter is also a pure sine wave, as if it's not, it may not work to drive a microwave either.

You can setup a van to drive a microwave on lead acid, but youll need more than one battery to do so, likely between 2 and 4 depending on the rating, and even thats pushing most batterys to their limits. You'd be better using 1 or 2 correctly rated Lithium batteries though.
Putting together cheap components does require you to run the maths on things like peak current flow, and make sure your battery, fuses, are rated for them.

You can't expect to run a Microwave on a single lead acid and have it work, you are pulling near 80A from a single battery (current draw), and a lead acid battery is rated at around 1-2C max, ie, 20A is all you should pull from a single Lead acid ideally (20A on a 100A battery is the 5 hour rate, which usually derates a 100AH battery to about 80AH)...
Lithium's are rated for usually 3-10C, ie, you can pull up to 100A per BMS typically, or 1000W ish on a typical modern Fogstar (read the spec sheet for max current draw).. So to drive a 3000W inverter you'd want potentially 3 Lithiums.

Even trying this on a single lead acid may have cooked your battery I'm afraid, it's well beyond manufacturing tolerances for a single lead acid to attempt to pull that kind of current. And if you've got a cheap microwave, is your inverter a pure sine, as if it's not, it may not run a microwave fullstop anyhow.

So it's not really a head scratcher, its you trying to use a battery well beyond the manufacturers tolerances. You need lithium or more lead acid. Nothing else really. Try looking at the spec sheets for the batterys you want to use, and make sure they are capable of actually delivering 3000W (lead acid can't deliver beyond the 5 hour rate typically (ie, divide the battery capacity by 5 (ah capacity) and thats your PEAK current per batetry).

 

[oldiesontour]

Obviously the lower the wattage of the microwave the better,the shorter the cable between the battery and inverter the better.
Your van battery/engine running may help a little but as it will be connected to the leisure battery A by a relay that won't be rated anywhere near the current your trying to draw B. The same applies to the cable between the batteries,you risk taking fuses out or if not properly fused much worse.If you put two LBs in parallel with minimal length cables all round and good earth's you may just get it to work...but it will shorten the life of your batteries .50mm cable would be better at reducing voltage loss.But lead acid is just not designed for sustained high current draw and voltage will drop under load

 

[Frm2005]

Yeah, needs to be a lithium battery and you may need 3 for that kind of draw. Depends on the BMS rating in the Lithium battery.
You can't draw that kind of power from a lead acid battery, it (as you have discovered) can't deliver that amount of charge rating.

We run that kind of thing on an Ecoflow Delta2 in our van (an all in one Lithium battery and inverter, able to deliver 2000w sustained 2400w peak pure sine wave). These can deliver that kind of flow as the BMS in them is rated for that kind of draw. Even most Lithium batteries will be limited in peak flow to likely need 2 of them. You could do it yourself, but you'll need to pick the right Lithium battery and BMS to deliver that kind of flow to your 3000W inverter. I presume the 3000w inverter is also a pure sine wave, as if it's not, it may not work to drive a microwave either.

You can setup a van to drive a microwave on lead acid, but youll need more than one battery to do so, likely between 2 and 4 depending on the rating, and even thats pushing most batterys to their limits. You'd be better using 1 or 2 correctly rated Lithium batteries though.
Putting together cheap components does require you to run the maths on things like peak current flow, and make sure your battery, fuses, are rated for them.

You can't expect to run a Microwave on a single lead acid and have it work, you are pulling near 80A from a single battery (current draw), and a lead acid battery is rated at around 1-2C max, ie, 20A is all you should pull from a single Lead acid ideally (20A on a 100A battery is the 5 hour rate, which usually derates a 100AH battery to about 80AH)...
Lithium's are rated for usually 3-10C, ie, you can pull up to 100A per BMS typically, or 1000W ish on a typical modern Fogstar (read the spec sheet for max current draw).. So to drive a 3000W inverter you'd want potentially 3 Lithiums.

Even trying this on a single lead acid may have cooked your battery I'm afraid, it's well beyond manufacturing tolerances for a single lead acid to attempt to pull that kind of current. And if you've got a cheap microwave, is your inverter a pure sine, as if it's not, it may not run a microwave fullstop anyhow.

So it's not really a head scratcher, its you trying to use a battery well beyond the manufacturers tolerances. You need lithium or more lead acid. Nothing else really. Try looking at the spec sheets for the batterys you want to use, and make sure they are capable of actually delivering 3000W (lead acid can't deliver beyond the 5 hour rate typically (ie, divide the battery capacity by 5 (ah capacity) and thats your PEAK current per batetry).

Wow, you seem to know your apples when it comes to this. I just want to warm a pre cooked meal in the back of the van. What do I need? Obviously my current set up doesn't cut the mustard. It worked ok in the old van but I'm open to suggestions. I want to be able to buzz some pre prepped food in the back of the van when away on business. What do I need?

 

[oldiesontour]

Ideally a lithium with 200amp BMS ( and decent psw inverter) or a power pack .

 

[starquake]

Wow, you seem to know your apples when it comes to this. I just want to warm a pre cooked meal in the back of the van. What do I need? Obviously my current set up doesn't cut the mustard. It worked ok in the old van but I'm open to suggestions. I want to be able to buzz some pre prepped food in the back of the van when away on business. What do I need?

Cheapest/quickest way is a Ecoflow Delta2 imho. Others will differ in their view and say build your own, but I've found it cheaper/easier to just buy a small all in one solution. It recharges off your cig lighter when driving, OR via solar, OR via mains (or a combination).

If you do insist on building your own, you should try thicker cables as above (50mm) should reduce the voltage drop and may make it work with 2 leisure batteries. If you do not have a pure sine wave inverter it may not work on some microwaves anyhow, so you'll need to swap for one that is pure sine.

I'm not saying it's impossible, but a sustained (10 min + load) of a microwave or airfryer to reheat, needs 2 minimum lead acids, or 1 minimum 200A BMS (ie, 2000w) rated lithium connected.

Trying to run a 3000W inveter on a single lead acid just won't work, thats a peak load of 250A.

The reason these Ecoflow units work, is they don't have 2 metre runs of wiring between the battery and the inverter, or the voltage drop involved, thus don't need to cater for the voltage drop on the wiring. I suspect your cabling should be 50mm as above from my basic putting your figures in a wiring size calulator to stand a chance of this working.

^{_{Subscribers  do not see these advertisements}}

 

[starquake]

I can confirm (as have one in our van) a Delta2 can run an airfryer for a 30 min cook just fine (but it does use half the battery!).

 

[oldiesontour]

Depending on what inverter you have A lot of unbranded ones claim to be PSW but are infact Modified sine wave

 

[starquake]

Depending on what inverter you have A lot of unbranded ones claim to be PSW but are infact Modified sine wave

Agree, and these won't work for modern (inverter based) cooking implements typically.
The issue with the cheap inverters is there is no guarantee on the cheap Chinese imports and short of putting them on a Oscilloscope yourself no way of knowing.

Brands that I know do decent Pure Sine wave that actually are include Victron.

If it's worked (the inverter) for you in your old van, chances are the inverter is fine, it's voltage drop on the wiring causing it. ie, extra battery and thicker cables.

 

[oldiesontour]

Agree, and these won't work for modern (inverter based) cooking implements typically.
The issue with the cheap inverters is there is no guarantee on the cheap Chinese imports and short of putting them on a Oscilloscope yourself no way of knowing.

Brands that I know do decent Pure Sine wave that actually are include Victron.

If it's worked (the inverter) for you in your old van, chances are the inverter is fine, it's voltage drop on the wiring causing it. ie, extra battery and thicker cables.

A good indication of psw is try a fluorescent tube ...they often won't work on dirty power.
Other names Edecoa,Renogy,Reliable power,generally if it is £120 for 3kw psw ...it either ain't PSW or it ain't 3kw

 

[Kannon Fodda]

A microwave will often pull double it's rating at startup. So the 800W microwave needs at least a 1600W supply. Ignoring that there is inefficiency in inverters, that at 12V means some 72Amp is being pulled from the battery systems. Not sure how the previous van coped with that but as above few lead acid battery types will be happy with much more than 20Amp draw. They may briefly do more but will suffer and shorten life.

Lithium (lifepo4) is more versatile and those batteries can usually handle 100A current without a difficulty. Problem is that your wiring needs to be compatible for recharge. Hence self contained power packs may be a better solution in a smaller camper orientated van that you only spend a day or so out and about.

Also loo at wiring from battery to inverter. Too small a cable invokes heavy resistance and thus cable overheating and voltage draw (latter contributing to the warning signals). A 3000W inverter really needs at least 50mm sq cables for less than 1.0m length between battery and inverter.

^{_{Subscribers  do not see these advertisements}}

 

[Jev88]

As well as increasing batteries so they can tolerate the high demand you can also buy microwaves with reduced wattage down to 500w with a soft start circuit to reduce the initial spike in demand - for example from Kitchenwareonline who convert them for truckers.

 

[Richard n Ann]

want to be able to buzz some pre prepped food in the back of the van when away on business. What do I need?

Have you got a gas oven? I occasionally use ours for warming up a curry and it takes about half an hour. It also warms the van up nicely for UK camping

 

[Frm2005]

Agree, and these won't work for modern (inverter based) cooking implements typically.
The issue with the cheap inverters is there is no guarantee on the cheap Chinese imports and short of putting them on a Oscilloscope yourself no way of knowing.

Brands that I know do decent Pure Sine wave that actually are include Victron.

If it's worked (the inverter) for you in your old van, chances are the inverter is fine, it's voltage drop on the wiring causing it. ie, extra battery and thicker cables.

Thanks for your advice here, looking at the numbers the Delta2 would be the cheapest option. How long does the delta2 take to charge? This is the inverter I have.

https://www.amazon.co.uk/dp/B07SBLTWRG?tag=mhf04-21

 

[starquake]

Thanks for your advice here, looking at the numbers the Delta2 would be the cheapest option. How long does the delta2 take to charge? This is the inverter I have.

https://www.amazon.co.uk/dp/B07SBLTWRG?tag=mhf04-21

Depends on how you powering it, but on mains it takes about 60 mins to do a 80% charge at max speed (you can control the speed with app so if you have longer you can charge slower). On Solar it takes 400W so about 2-3 hours if you have 400W of solar connected and it's empty and the sun is full. On the cig lighter it charges at about 120W, so about 5-6 hours as you drive. You can get other Deltas from Ecoflow that offer varying storage and power output requirements, but I can confirm I've ran a normal microwave, along with a small airfryer on mine, as well as a toaster and kettle (low wattage). Ecoflow sell an additional cost B2B charger if you need faster than 120W charging, that directly is wired into a vehicle, to allow far faster charging in addition. I wouldn't personally say get that, as solar on your van roof is probably more useful and also cheaper!

It's why many of us own Delta2's -> it's quite cheap when compared with batteries when you actually size the batteries and inverters for an equivalent size. Some people also upgrade their vans to Lithium and put in Victron gear, but you are looking at a bill of around £1200-2000 for that.

BTW - > That inveter is 6000W peak, no wonder you stuggled! Thats a 500A startup surge as it energises at 12V. It's probably modified sine (many of these chinese inverters actually would only deliver about 2000W sustained too), despite it saying Pure Sine, but would probably work fine if it had enough batteries connected in all likelihood, but looking at those amazon photos the wiring is dangerously (fire risk) undersized that came with it. IF that continued to the build inside, I would be worried a bit personally about the quality of the inverter, given they are not supplying from the looks of it with enough copper to allow the inverters capacity to be reached. That said, a quality Victron pure Sine at that rating would be > £800.

(I also can confirm btw, Ecoflow do use Real Pure Sine waves, which is why their kit is such a good price).

 

[oldiesontour]

As said by Starquake the power pack is probably your cheapest easiest option..other than adding more lead acid..Again unless you can DIY lithium is going to need a B2B. The battery it's self plus fuses,cable,isolator etc if you use your existing inverter for mid market kit fitted £700 minimum totally DIY £500 ISH.
2 new 110ah lead acid £200 + a low wattage mwave + decent install DIY may be £400 ish