Want to build a portable Charger

Hey guys…

I have a 12S4P on my Mountainboard. While I can get far enough for a satisfying ride I wouldn’t mind having another extra 1 or 2P’s on demand.

So I was thinking about building a 12S1P or 12S2P Portable Pack that will be used to charge the 12S4P.
So does anyone have experience with some tested circuitry to limit the current properly ?
Maybe I also have to build a 13S1P instead to be able to have enough charging voltage and limit the voltage as well.

Of course it would be better to just build a whole new pack that is 12S6P in the first place but I was just thinking about the on demand solution where I can still have my relatively light weight board when I don’t need the extra Amps and then just carry a portable pack whenever needed.

Anyone thought of a solution to this already ?

A LM317 could be used to limit the current I guess and there are also many voltage regulators available (LM317 can also be used to regulate voltage). However I never built a charging circuit yet (only power supplies)…

So paired with this it would be possible to have an adjustable portable battery pack that can charge the battery pack of my board. I could install two meters (one for current and one for voltage) to monitor everything.

The Bad thing is that the LM317 only is rated for a maximum of around 40V Output :frowning:

The LM317HV might fit the bill ?

So any ideas guys ?



If you do a 14s charger then it can top off the main pack when it’s dead, only need to step down then
3.6 * 14=50.4
4.2 * 12=50.4


This is the easiest solution for sure. Just get a simple step down module with built in current limiting.


Sadly all of the step down converters with current limiting only go up to around 32V. So I would have to build something custom for my 12S Setup.

This one might work… Input up to 60V and Output to 50V with a maximum of 20A that can be regulated to any setting you want…


Might go for something like this… super versatile


An alternative that requires no modification other than a discharge bms is an ac inverter for a car…

Run a 4s battery into an inverter and use that to power your 12s charger.

Effeciency would drop a fair amount and the size would be a bit bigger, but this is a stupidly simple solution if you dont care about engineering something

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Yeah I thought about that but the power/efficiency loss made it a no go for me :frowning:

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Btw, can i get a link to that adjustable converter? I would like to look into that for a non esk8 related project.

Sure you can… I got the exact same one already but for lower voltages - I use it as my lab supply it’s perfect for DIY Projects and to limit current to detect shortcircuits etc.

Basically they are called DPS you have many variations available:


Those prices are amazing… i thought it would be closer to $100 usd for something so versatile.

100usd is 89 euro if that helps

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Yeah… they are super cheap - there is also versions available with bluetooth etc.
I have mine running for years without issues… also EEVBlog reviewed one of those and said it’s a really good product for the price

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Well tomorrow im going to do some research and pick up a few of different sizes. These are much needed, i just didnt know they existed.

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So yeah basically with this DPS it is possible to make a 14S Pack and regulate it to a charging voltage of around 50V and limit the current to around 4A.
Then as the 14S Packs gets “drained” the output voltage will automatically fall off and probably stop charging by itself.

So that should be safety enough to not overdischarge the charger pack (I guess)…

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Also thinking about it more properly… I am about to build a 0-50V Portable Lab Power supply with 20A Current… I mean… this would be perfect not only for esk8 but for basically…



This subject always interested me.
For this particular case though, since you have a top mount enclosure, how difficult is it to make another 12s4p and change them out on the trail?

I have been thinking about doing that for my Trampa since the way it is wired, I can just slam another battery on top without having to even mess with opening the box.


Basically it comes down to that my battery pack is designed inside a case including the BMS and it’s such a super tight fit that its not just plug and play… you have to manage the cables down to the micron to get the case to close… but I get your idea…

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Do you use a loop key?


Anti Spark Switch and a Button… which also sits in the same box with literally a negative amount of space around it (black hole paradox)

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Sounds like you need a bigger box :rofl:

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