In the field RC LiPo charging

Batteries and Chargers Rechargeable Batteries
1

Hey everyone,

Complete new boy here so be nice and simple with any replies.

I have a question regarding the powering of dedicated 12v chargers, used to re-charge 2S LiPo packs used in RC cars and buggies, the 2 normal ways are to have a large capacity Car / marine battery, or to take a small generator.

My question is, would it be possible and practical to use one of the smaller Power station/ banks available on Amazon and other sites for a clean and easily transportable option ?, I have asked around and have not found anyone who can give a definitive answer on the possible use of a Power station (example added below).

The LiPo I would need to charge are. https://hobbyking.com/en_us/turnigy-nano-tech-ultimate-4600mah-2s2p-90c-hardcase-lipo-short-pack-roar-brca-approved.html?queryID=3ebf7cf1706e50f0454e9c7af1cd7253&objectID=30790&indexName=hbk_live_magento_en_us_products

The type of Power station / bank is. Amazon.co.uk

So the maths completely confuses me, I need to understand if the capacity of the Power station would be capable of powering a 12v battery charger to recharge the above LiPo cell packs a total of 10 times in the field.

Many thanks for any replies and info / suggestions.

2

So the question is whether a battery pack can be used to charge another battery pack (with the correct charger in between)?

If so, the answer is yes. I have seen people use all kinds of batteries from automotive lead batteries to marine applications to DIY lithium packs to power their hobby charger.

check what requirements your charger has and see what works.

(i.e. my hobby charger goes from ca. 11V to 20V)

3

Thank’s for your reply, I understand it will work, my main question is how many full recharges of the Lipo could I expect to get.

If I will only get say 6 charges from the Power bank, it would not be enough for a days racing, as I said its the maths that I have no clue on.

4


Number of charges is equals to your source capacity divided by your battery capacity

Source capacity = 412 Wh (As advertise not sure if true)
Battery capacity = 4.6Ah * 7.2v = 33Wh

412/33 = 12 Chargings but this is not so including power loss and I rounded some numbers so lets say 8-9 if advertised numbers are correct

5

Thanks YuvalS, that’s what I was expecting to hear, the margins are too close to make this a viable option.

6

Welcome to BLF!

In addition to the capacity of the large bank being possibly lower than advertised, please also keep in mind any step up or down in DC power causes some loss to heat. Even more so with DC to AC and vice versa (about 15% loss for that alone). If you already have 12V DC chargers, I would suggest considering a power bank that has 12V cigarette lighter output to eliminate one step of voltage conversion. A rule I use for calculating minimum capacity needed is:

Total Wh needed / 0.85

So in your case:
33Wh x 10 charges = 330 Wh
Divided by 0.85 = 388 Wh (minimum power bank capacity needed)

I’ve used a 500 Wh Jackery power bank to run a 12V electric blanket off the cigarette socket all night for camping. The blanket drew an average of 30W per hour. It pack held up nicely and still had about 40% remaining (very little loss and capacity seems to be as advertised). The Jackery solar panel charged it back to 85% in a full day of winter sun.

Depending on your budget, a larger pack is a viable option for your needs. The cost for reputable brands in the US is about 85 cents to $1 per Wh capacity. More for bells and whistles like USB-C quick charging, built in solar panels, etc.