Recently bought a remote car and the battery seems to have died. The car runs slow even after i charge the battery for hours.
Where can I buy this rechargeable or disposable?
It’s two 18650 cells in series. You should be able to buy on robu.in. But I didn’t see any packs with this exact connector there - https://robu.in/product-category/batteries/batteries-batteries/li-ion/2-cell-7-4v8-4v/
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EDIT: Looks like this is “SM4P” connector, I can see a few such packs on amazon.
@rsaeon might know more.
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That’s a 4pin jst sm connector, Amazon has a few batteries that should be direct replacements if the wire colours line up. Other places would be cheaper, it’s literally just two cells and a wire.
how does charging happen on these? I think there is no BMS inside the 18650s? So can two 18650s in series be charged just like that?
Can you show it’s charger?
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There is a BMS inside for sure.
Thanks for the info @roadrash99 @rsaeon
Found one with similar specs for a $ on Alibaba
Do i have to get a similar mah battery or 2000 will work too? I’m a total noob in electronics so idk much about this
The additional pins are for balance charging. Sometimes there’s protection circuit inside the pack but it’s technically not necessary since you’re connecting the middle wire as well.
The 4pin connector pack is the same as 3pin pack, middle two pins connect to the series connection between the cells.
These usually come with a USB charger, the balance circuitry is on that:
A 7.4v pack with a 2pin connector has a bms built-in, no doubt.
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You can always go higher, it’ll just take longer to charge.
There is no BMS in such packs.
They are meant to be charged with balance chargers hence the extra pins.
Each battery +/- is wired to the terminals and the balance charger will is responsible for getting each one to 4.2V
@warlock7x
I have way too many of these packs that need periodic replacements as my son are I are into RC track racing.
Eventually I started building my own packs as it turns out to be a fraction of the cost of pre built packs.
Having said that, you will need a spot welder to do this plus shrink wrap supplies so getting the equipment may not be worth it for just a one-off need.
For a one-off need, try ordering one off robu.in
even if its a 3 pin one, you can reuse the existing 4 pin JST as 2 of the 4 will be joint inside the pack to the middle serial connection
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It confused me, but yes now that I see it, this battery may does not have a BMS.
The 4 wires might be connected to terminals of both the batteries individually. The wire color gives it away.
- B1 + (red)
- B1 - (black)
- B2 + (red)
- B2 - (black)
Similar to this, not sure about the order.
So basically these batteries are 2 individual cells >> not << wired in series. What happens is when this battery is connected to the toy, the toy itself bridges two of the terminals, one from each cell, making it a 2S pack or it may not bridge it and use the cells individually.
This is a clever design by the toy manufacturers to save cost.
To the charger the battery shows itself as dual 1S cells, so each cell is charged individually, which becomes balance charging by definition without using any traditional balance charging circuitry.
But what about the protection? Over discharge? Short circuit?
I guess in these low value toys, where manufacturers are saving costs, they probably handle these in the toy itself, and I doubt they are using any standard practices.
I don’t know how this will work, because the 2S battery we buy from robu most likely will have a real balance charging pin with total of 3 pins.
and the toy itself expects a 4 pin dual 1S battery.
Sure with some tinkering we can bridge the pins in toy ourselves and connect this battery to the remaining two pins. This will work. But to charge this battery a real 2S battery charger will be required.
Getting the equipment isn’t worth it indeed. Can I buy it from you instead?
As in actual competitive racing?
Probably could just get a 2S holder and swap out the cells whenever they degrade too much to be usable.
I might also need a rechargeable battery replacement for my kids toy but the tear-down of the toy itself is a pita. Someday I will do it and ping you. Then suggest me the max capacity one For it but again max capacity shouldn’t mean a bulged fat battery which the toy might not accommodate.
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I cant find one that has an SM4P connector. The toy car has this connector.
Yeah, it looks like you’ll need to make one, but that shouldn’t be too hard since you’ve already got a dead-ish battery, just detach the wires and have a local technician solder them on to the holder.
Its not really a cost saving measure but more of a standard protocol for Li-Ions thats been in existence for long now.
Its a standard design for 2S/3S or similar serial packs. And is actually a good design since it makes replacements very easy since the cells are also standard sized.
Its LiPO batteries that usually come with BMS and not Li-Ion
As for the 3 pin pack vs the 4 pin pack, 4 pin for 2S is actually not exactly standard but 2 of the 4 will be wired to the serial connection between Batt1 + and Batt 2 - pin.
Can either be checked via a DMM (zero resistance/ zero voltage) or by cutting open the shrink wrap.
The 4pin JST connector will anyway need to be reused for this
Just get the 2S battery from robu.
Wiring it up to old JST is pretty easy and I can help you out with that.
Whatever you would spend on covering shipping can anyway be spent on a cheap DMM (multimeter) so that you can validate your connections easily.
As for track racing - this is not exactly a popular hobby in India.
That also makes finding proper hobby grade cars extremely difficult. Most toys available locally are binary throttle and steering .. at max you will find proportionate (analog) throttles
I have over the years picked a bunch of mid to high range hobby grade cars during travels - including 1:28 Kyosho Mini-Zs, 1:12 bashers and 1:43 micro units
I have also setup a medium sized track + lap timing setup that we use for the smaller units for lap speed runs and for races..
Its a fun albeit sorta expensive hobby though
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