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rik avatar image
rik asked

Welding via multiplus 48/5000/70 from 10kwh LiFePo4 (51.2v 200ah)... problems

Hi , previously I have welded off my old set of lead acid batteries via a cheapo 5kw inverter without any difficulties (stick welding via a small inverter welder typically around the 70-100a range with a 2.5mm rod).

Having upgraded to the multiplus and a lithium, I had dreams of being able to comfortably zap things together into the night without running the generator (10kw water cooled 1500rpm lovely thing it is too ).

What I've found instead is that upon striking up, very often the bms will shut the battery down for 10-20 seconds before restarting, or the multiplus will give a shutdown red flashing. Everything 'should' be well within specifications of both battery and inverter , but no ! Not only that , but if I am charging up from the generator and running the welder direct from the generator (ie not going via the multiplus), I still get overload problems .

What am I doing wrong ? ! It all used to work okay ! Even with my knackered set of 200ah 48v lead acids and cheap inverter ...

Do I need to look at my earthing ? Install some kind of capacitor ? A spike suppressor or something? I'm a very capable DIYer and been at this off grid stuff for 24 years , but the internal and programmable nature of this newer technology is making me feel old !

Help me Obi Wan !!


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8 Answers
nickdb avatar image
nickdb answered ·

What size, spec and model is your battery pack?

Unfortunately with lithium, size does matter, especially with bigger loads that surge. Factor in a low frequency inverter and you can have issues.

Battery requirements go up significantly without grid and lithium is not tolerant of leaving its comfort zone.

100A? Assuming that is DC. Can you be more specific on the load?

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rik avatar image
rik answered ·

100 amps DC on the welder shouldn't draw more than 3.5kw at 230v , at least that's to say it runs normally on a 13a fuse plug socket all day long.

What I don't know is if the striking up the arc produces a momentary spike that puts the lithium's fussy BMS's nose out of joint , and if there's anything I can do to smooth out the shock?

Thanks for replying, I appreciate it . Rik

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rik avatar image
rik answered ·

And it's an "Eco LiFePower" (dreadful brand name I'll grant you), 51.2v 200ah wall mounted battery with 16 cells . I haven't looked inside the thing to count them or to see any of the gubbins therein, I had trusted it did what it said on the box :

Recommended discharge current 100 A (5 KW)

Maximum discharge current 200 A (10 KW)

peak discharge rate 250 A for 5 sec

As far as I know, I shouldn't be exceeding the recommended discharge, I only have a 5 KW inverter , so I can't very well do any more ...

Anyway, I'm kind of clutching at straws . Thanks for reading. Rik


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kevgermany avatar image
kevgermany answered ·

Guys have used my EasySolar (which has the same multiplus in it) for welding without problems. But there's a much larger lithium battery bank behind it. Nearly 20kW/H. Guess it's your battery/BMS.

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Michelle Konzack avatar image
Michelle Konzack answered ·

I have the MultiPlus-II 24/5000 and have no problems using my new ESAB Rebel EMP235iC with 200A Welding current.

I run this Monster at 140A with ED100% and the MultiPlus-II only smile.


It is NOT your MultiPlus-II 48/5000, but the too small LiFEPO4 batteries...


I have currently 2940Ah (70,5kWh) of SOPzS Batteries, which can cope much better with Peak-Loads from a welder.

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rik avatar image
rik answered ·

Thanks Michelle , my purse thought 10 kwh would do the job , especially after looking at the spec sheet . I looked online to where I got the battery from last year and they're still selling them (annoyingly , even cheaper than then ! )... well , I'm going to get some help with the parameter programming and see if that helps , otherwise, back to the drawing board .


Thanks everyone for your replies , Rik

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matt1309 avatar image matt1309 commented ·
Hi @Rik


Cant throw a ct clamp on the battery could you? Or see montor data from BMS. Would at least confirm to you that it's the battery that's the issue.

I couldnt find your battery online but might be worth checking the BMS settings are setup correctly or at least see if it'll tell you what safety mechanism caused it to flag. (ie overcurrent or under voltage etc). Some of these BMS have bluetooth app for monitoring.

Does seem odd that the peak the multiplus can provide is less than the peak the battery can provide yet others are running similar loads on their multiplus fine.

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rik avatar image rik matt1309 commented ·
Thanks for your reply, I'll put a clamp on it in a day or two (out at work), and let you know how I get on .

The batteries are still online via ELP energy (annoyingly cheaper than when I bought mine ! Typical ! ).

Someone else has suggested some kind of filter to reduce spikes and 'noise' near where the welder is plugged in , but I don't know what to look for really in that respect.

Thanks again for replying. Rik

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Al avatar image Al rik commented ·
As others have mentioned, you probably need a larger battery bank, but do you have bluetooth to the BMS? Are the cells properly balanced? It could be a stray cell causing a low voltage warning.
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matt1309 avatar image matt1309 rik commented ·

'I cant spot mention of which BMS it uses to suggest if there's an app available to for you to see the data so think CT clamp is your best bet.


I reckon once you've got the numbers I'd go back to manufacturer. Based on what you've described and the fact others have managed to power similar load with the same inverters and the battery specs, sounds like you should be able to achieve those numbers easily but at least with numbers you'll be able to confirm it how some evidence for battery provider.


EDIT: is it just my understanding or is the welder on AC side?

So if battery spec is rated for max output of inverter and the inverter is determined to not be the limit then battery must be really under performing.

Unbalanced cells is a good shout! What SoC is the battery at when you're welding/is it less impacted when battery is near full?


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sharpener avatar image sharpener rik commented ·
Worth trying the kind of filter typically used on the AC inlet of washing machines and dishwashers. Will handle 2.2kW continuous and probably >3kW peak. Can probably get one for free from your local waste tip.
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Juha Tuomala avatar image
Juha Tuomala answered ·

Lead acid batteries are ideal for starting and can monetarilly give 500A or more. That certainly helps in welding application as well. Sometimes I wonder how lucky people were that such early chemistry allows electric starters for primitive combustion engines almost 100 years ago.

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Michelle Konzack avatar image Michelle Konzack commented ·
I have installed a Customer 3 Quattro 48/15000 with a singel set SOPzS 4350Ah 48V (200kWh and 160kWh usable) and nor the Quattos or Batteries have a problem running a VERY BIG (I think, it is max 460A) 3-Phase welding machine from ESAB.


The impulse which go trough the Inverter to the Batteries is so high, that if my customer would have used LiFePO4 Batteries, the would have been around 500kWh, while the SOPzS cost only 18.000€...


You pay already for a DIY 16S 320Ah (16,3kWh) LiFePO4 with 200A BMS over 2000€ hence you would need 40 LiFePO4 sets which cost 60.000€ to get this installation running. Since you can not put 30 Sets separately parallel, you have to put al least 5-6 cells parallel and this is where to REAL problems start.


Nothing for El-Cheepo DIY.


It will create real headaches and get very dangerous.


Hence for industry applications including welding @home Lead-Acid Batteries is the way to go.

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Al avatar image
Al answered ·

@Rik To add to my comment of checking if the cells are balanced.

Do you have the battery connected to the Multi and a GX? You can see the error codes, or looked at the advanced widgets on VRM for the battery to see what's happening whilst welding?

As a side note, if it is this battery: https://www.elpenergy.co.uk/product/51-2v-48v-200ah-lithium-lifepo4-wall-mount-batteries/ and you have not changed the charge settings then you're overcharging the cells and they wont last long! Charging LFP to 3.65v is already unnecessary (3.45v - 3.5v is easier on the cells) but the data sheet says termination current / tail current is 100mA, that will quickly overcharge the cells. Termination for 200Ah cells should be 10A minimum @ 3.65v

See here: https://nordkyndesign.com/charging-marine-lithium-battery-banks/

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