Powertool batteries to power inverter (mobile power station)

China Man

China Man

China Man

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22 Oct 2002
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London
I have seen some products that you can buy off the shelves to power 230V but they are really expensive and often limited in power.

Makita brand such as BAC01 which will require a 36v battery pack that you buy separately. Ali Express usually have the 1-2 batteries small inverter of 300W which is not really useful for camping etc.

I found a 36V inverter on Ali and some ready made battery brackets with wire out, I will be starting a built thread and hopefully a video for my channel. My goal is to make one which is powerful enough to run a rice cooker (Chinese we can make a lot of dishes from rice cooker). Any one done it before?

My plan is to run 10x 5ah batteries, 2x18 in series to get the 36v and then 5 pairs in parallel, I get lots of batteries for review so I have plenty for the built. It will be a one way system as the batteries will still need to be charged via mains individually, I do have home solar and I can charge the batteries at home with excess solar or cheap rate at night.


 
I understand as a lay person it would be crazy to make your own as you can get an off the shelve unit for around £800-£1000. I already have around 20x 5ah Makita type battery and will be getting more for free so it will be a way for me to use/test the batteries as well as a fun project. I intend to spend no more than £150 and I already have terminal crimps and big gauge cables etc.


I already have an off the shelve mobile power station but it is only 300W which is great for the odd laser engraving off site and recharge with a small solar panel, I though I would go bigger this time

 
China Man said:
My plan is to run 10x 5ah batteries, 2x18 in series to get the 36v and then 5 pairs in parallel
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36V x 5Ah x 5 pairs = 900Wh.

So your proposed system can provide in total 900W for an hour, assuming it can deliver the current. It might have to be 450W over 2 hours. Maybe you can get 1800W for 30 minutes. I don't know what the max current is on those batteries.

How much does the rice cooker use, peak and average?

Seems like a bulky and risky way to deliver minimal energy. Statistically you're running 10 battery sets. If those are off brand items I'd not like those odds!

I'd probably rather buy a car battery with 60-70Ah. That will give you similar total energy with a single item to charge, less wiring, MUCH safer. Even buying a bag full of quality 18650 cells would be a better idea.

Fun project though :D
 
We use a small rice cooker which is around 300-500w and cooking rice with it will be around 20 minutes.
I have induction cooker which has 2 sides total 2800W, I am sure it will be once side only and choice of 100w to 1000w and not 1000w to 1800w

A car lead acid battery is a no go, they don't discharge like lithium. A bag of 18650 will need a lot of wiring and BMS which would be a lot more risky than the 18v pack which is already wired?

The battery holder with lead is only a few quid each, I can add more if needed. Once the 10 battery pack is made it will be just add more to the busbar anyway.

Lets see how it goes, apparently there are already company and also another crazy person making these.....


I doubt mine will be as neat as I will not open the case of the inverter but to built a separate battery pack but link it together.
 
I'm sure it'll probably work, you'll just need to ensure you limit the current draw from the batteries.

Most 18v power tool batteries won't want to output more than about 8 amps continuously as that's what most first party inverters are rated for (150watts for an 18v pack), so i'd try and stay within that limit as they'll know what they're doing with their calcs.

Seems like most power tool batteries are rated between 1 and 2 C so for a 5ah battery i'd really not want to go higher than say 7 amps personally if you value their longevity.

So with your 10x batteries that should be 1440 watts before losses if you want to push things. But you'll only realistically be getting 30 minutes of run time assuming all the batteries all in good health
 
Every 6 months or so I get some batteries for review, I may end up making a 20s since it will be just another board with the battery clips :)

My appliances which I potentially be using is relatively low power, my rice cooker is 400w and rice only is 15mins max to cook 4 people rice, with meat and veg is around 18min max for 4 people, Instapot is 1000w and it will take 20mins to pressurized when full for strews it is usually less then 10 mins then low power to keep it under pressure.



I guess the inconvenience is to charge the batteries as this is a one way system, each batteries needs to be charged separately. I have one single and a double charger so I can charge 3 batteries at once only. Need to find a solar solution to that if I am going on a long trip etc.

Got another free battery as I type :) now I have 22 batteries lol

 
China Man said:
We use a small rice cooker which is around 300-500w and cooking rice with it will be around 20 minutes.
I have induction cooker which has 2 sides total 2800W, I am sure it will be once side only and choice of 100w to 1000w and not 1000w to 1800w

A car lead acid battery is a no go, they don't discharge like lithium. A bag of 18650 will need a lot of wiring and BMS which would be a lot more risky than the 18v pack which is already wired?

The battery holder with lead is only a few quid each, I can add more if needed. Once the 10 battery pack is made it will be just add more to the busbar anyway.

Lets see how it goes, apparently there are already company and also another crazy person making these.....


I doubt mine will be as neat as I will not open the case of the inverter but to built a separate battery pack but link it together.
Click to expand...
I can't imagine taking that on a camping trip, it looks more of a burdon than anything else.
 
lol, not everyone is Bear Grylls. It does takes up space in the boot but the luxury of not having to start fire or bring coal.
 
The inverter and battery holders arrived and I spent 5 hours putting it together and did some quick test.
Powering my mini heat gun of 250w for 15 minutes and everything is cool to the touch. It was well into mid night and I did not want to start proper test in case of fire etc so called it a night. Over all it weight 10kg and almost all the weight is from the 10 18v batteries.

The Makita compatible 18v batteries have rating of 90-99Wh and of course with age and manufacturing BS it would be less than that in real life. My next video will be testing it in my garden running my 400W rice cooker, 1000w insta pot and then my induction hop, it should be fun




 
China Man said:
lol, not everyone is Bear Grylls. It does takes up space in the boot but the luxury of not having to start fire or bring coal.
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I do a fair bit of camping and would never bring a rice cooker with me. Have you considered gas? You can get a Campingaz Twister Plus which takes CV470 cartridges that you can buy practically anywhere in the entirety of Europe. It'll take up less space than that battery bank and inverter while being a lot lighter. Generally find a medium pot is enough to cook on for 4 people which this setup can just about take. For larger scale cooking I'd be looking again at something like Campingaz Bistro 3 with CP250 cartridges for bigger pots. A single pot + gas is much more versatile in a camp scenario imo
 
lol, I am Chinese and can't do without rice, when I say camping it is more like glamping and not back to nature and backpack / tents.....

I would not bring a power station if I am doing survival in the wildness, most likely driving to a site or park and start cooking on a picnic table (no open fires allow places)
:) If it is only for cooking I guess a gas stove and can would be the way to go and we do that with hot pot cooking at the table anyway. This would be for a lot of different uses, just like any power station on the market.
 
I had considered making something similar to what you are trying, except i didn't have batteries already so in that scenario I was going to buy 4x 105Ah LiFePo4 cells to make a 12v pack, a BMS and then add a 500VA inverter on the side for consumption. I was then going to to use something like Victron blue smart charger at wall power to charge it up and potentially have a SmartSolar MPPT at the car so i could bring it back to the panels to charge. Basically making a diy power station except the charge components are separate to make it more portable

In the end though i thought it was OTT for what i wanted and ended up just getting the MPPT charger and connecting it to the car battery/panels for when i don't move it for several days to keep things topped up while i use it for charging/lighting etc
 
Gammawolf said:
I had considered making something similar to what you are trying, except i didn't have batteries already so in that scenario I was going to buy 4x 105Ah LiFePo4 cells to make a 12v pack, a BMS and then add a 500VA inverter on the side for consumption. I was then going to to use something like Victron blue smart charger at wall power to charge it up and potentially have a SmartSolar MPPT at the car so i could bring it back to the panels to charge. Basically making a diy power station except the charge components are separate to make it more portable

In the end though i thought it was OTT for what i wanted and ended up just getting the MPPT charger and connecting it to the car battery/panels for when i don't move it for several days to keep things topped up while i use it for charging/lighting etc
Click to expand...
If going down the BMS and Lifepo4 route then I would just buy off the shelve, the tech is getting popular and price is much more reasonable than a few years ago. EcoFlow gets my vote if I am spending my hard earn etc.

It is so sunny outside so I did the tests of the inverter.

Cooked "magic rice" with the 400w mini rice cooker
Boiled 0.8L of water with the 250-100w mini kettle
Pan fried egg and frankfurters 1200w induction hop

Non of the cable, inverter casing, batteries got above 25c outside is 10c and sunny. The Thermal camera pick up more heat from the sun on the battery black casing than the battery working hard. The inverter fan did not come on once and only activated when I turn on both side of the induction cooker and it start to draw 2300W, inverter not happy and start beeping for a minute or two before I chicken out and turn the stove off. At 11kg it is neither here or there, heavy yes but not impossible to move around with one hand.

Over all my plug in power meter show 0.35kw used and the inverter battery indicator showing 40% left, not that I would draw anywhere close to 2kw for the last 40% without knowing if the built in cut off protection will work or not. I was a nice and easy project and I have some good footage for YouTube etc. Another £25 for 10 battery clip and I get myself a nice backup power generator :) 1800wh lol

 
China Man said:
If going down the BMS and Lifepo4 route then I would just buy off the shelve, the tech is getting popular and price is much more reasonable than a few years ago. EcoFlow gets my vote if I am spending my hard earn etc.

It is so sunny outside so I did the tests of the inverter.

Cooked "magic rice" with the 400w mini rice cooker
Boiled 0.8L of water with the 250-100w mini kettle
Pan fried egg and frankfurters 1200w induction hop

Non of the cable, inverter casing, batteries got above 25c outside is 10c and sunny. The Thermal camera pick up more heat from the sun on the battery black casing than the battery working hard. The inverter fan did not come on once and only activated when I turn on both side of the induction cooker and it start to draw 2300W, inverter not happy and start beeping for a minute or two before I chicken out and turn the stove off. At 11kg it is neither here or there, heavy yes but not impossible to move around with one hand.

Over all my plug in power meter show 0.35kw used and the inverter battery indicator showing 40% left, not that I would draw anywhere close to 2kw for the last 40% without knowing if the built in cut off protection will work or not. I was a nice and easy project and I have some good footage for YouTube etc. Another £25 for 10 battery clip and I get myself a nice backup power generator :) 1800wh lol

Click to expand...

Very nice, but how do you charge it ?
 
At the moment charging it 2 at a time with my makita chargers, have not figured out how to charge them safely in bulk.

To be honest I think I will just stick with that as this will not be used all the time and more a fun project
 
Bulk charging lithium batteries is a pain in the rear - very few off the shelf products for the task and quite a lot of complications to DIYing it safely.
 
Rroff said:
Bulk charging lithium batteries is a pain in the rear - very few off the shelf products for the task and quite a lot of complications to DIYing it safely.
Click to expand...

Tell me about it....

I certainly would not want to be in China man's shoes, I can just imagine the frustration when his Mrs says

" Dear, can you pack your gizmo for tomorrow's trip, I'll whip you up a nice treat with the stove"
 
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