Using a lipo for DC/DC charging.
 

For the knowledgeable peeps out there?!

I want to get a lipo to use to field charge my smaller lipos off my DC/DC charger

I want to be able to charge 2S and 4S with a max capacity of around 2000mah

I’m trying to get my head around the voltage part

Obviously upping the mah of the supplying lipo will give more charges but would it be beneficial to up the voltage of the storage lipo?

You only need to make sure that the supply battery provides enough voltage for the charger, and has sufficient capacity. Increasing the supply voltage beyond what the charger requires won't be beneficial (unless you're using something like an iCharger doing high current charge rates, which I wouldn't recommend).

Also, I'd recommend hooking up a voltage alarm onto the supply battery so you don't discharge it too far.

Thanks

So I’d be better off getting a higher mah 4S then a 6S

I use an iCharger at home but this is for an ISDT DC/DC charger, also as my charger is a dual charger if I wanted to charge two 4S lipos how would I need to up spec the supplying lipo?

That depends on the specs of the ISDT charger. Does the charger manual tell you the input requirements to do what you want?

If you want to charge two 4S packs off one 4S pack, that supply pack is going to need a very high capacity. You might be better off with a deep cycle lead acid battery for the supply.

This is the spec

https://cimg8.ibsrv.net/gimg/www.rct...e43383c7c.jpeg
I use a 24v power supply at home so really I’d never need to charger 2x 4S lipos but would definitely want to charger 2x 2S 300-400mah lipos as that will be at the club races I go too.

Max input current of 35A does limit the power output based on input voltage, so yes you actually might see a performance variation with a lower voltage input. What current do you charge your 2S packs at?

My 1/28’s only use a 330mah-360mah lipo so usually 1c-2c

As said I use an iCharger off a decent PSU at home and comps etc but for the fun one night a week club racing I used to just take my 2S lipos precharged but there’s obvious downsides to this, hence the ideal of just taking the small P20 charger and a 4-6S 5000mah lipo with me.

This is the main purpose of my idea but off the back of that it would be nice to have the back up of being able to charge a 4S if needed, but then I guess to do that I’d already have to have the supplying lipo already charged and I do have a audio dry cell car battery in my van I had from my car audio days 🤔 maybe I need to rethink that part!
But still ideally I’d like to be able to take one decent precharged lipo with me each week and charge my smaller 2S lipo’s off it at the club!

Thanks for all the advice 👍🏼

So you want to drain one LiPo battery to charge another.......

It is indeed a better and much cheaper choice to get a small car battery. For sure at a junk yard you will find a cheap battery.

Yep!

I do have a dry cell battery but again the same applies to my 406/PSU set up, I only want to travel light and only need to charge up at max 6-7 360mah lipos

As I’ve said I race 1/28 scale which use tiny 2S 330mah-360mah lipos now at proper events I’ll take my iCharger and PSU but once a week we race at a local community centre I planned on using the small ISDT P20 DC/DC charger and take a single charged 4/6S 5000mah lipo to use as the supply to charge the smaller ones?

Apologies if it’s a stupid request for advice but to me seems the most logical way around it!

There is sockets at the venue but not many and then that would require setting up with extension leads etc and dictate where I can place my kit.

I could just buy a heap of the 2S lipos and charge prior to going but that would require me buying a few plus on some nights I’ll only go through 3 packs over days 6-7 so seems more seasonable to just take one large charged lipo as I can then use it to charge and what I don’t use I can balance charge my other lipos etc

Plus the single lipo would only mean one charge and one storage/discharge depending how the race went so more convenient then having to charge and discharge multi lipos once a week.

Sounds like you'll be charging at less than 1A per channel. At that low rate, input voltage won't matter.