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My Grandson loves his Batman RC car, but it needs 4 x C type 1.5v batteries, which are heavy and don't last long enough for him.
I'd love to convert it to be rechargeable, but if that's too complicated, then maybe just change the battery connector to a male or female plug and buy a made battery pack with a USB charging plug/lead.
It's a heavy toy, so I think that's why it needs 4 c batteries, because they hold more Ah than AA's.
I'm a little unsure if I need a battery that equals the average Ah of 4 C's at 1.5v, or if I need a 6v battery?
How do I work this out as I don't have any of the box, instructions and he's had it a while and his Mother cant remember where he got it, so searching for it has yielded no results so far.
The C's go into the toy with opposites in a line (so c1=+2-, c2=-2+, etc) so down one side of the battery tray across all 4 batteries you get plus, minus, plus, minus - make sense? I think this means they are configured in series? if so this mean it's a 1.5v circuit?
And now my head has exploaded lol.
I'm fine with soldering a BMS( battery management system) module into it, along with cutting a hole in the toy for a charging wire, but I have no idea which BMS module to buy or if I even need one or if it would be better to just get a pair of plugs and connect one to the battery cables in the toy.
I'm looking for pointers on how to go about this and to learn how to work this out for myself in future.
Thanks in advance,
Posted : 18/01/2023 9:00 am
Welcome to the forum! Can you share a picture of the battery holder? It would be quite surprising if they're wired in parallel to yeild 1.5v, as 6v seems more sensible for a heavier rc car.
That's really the first thing to determine.
If it turns out that they're wired in series for 6v, then two lithium batteries might work for it quite well, although you'll have to make sure that they have a protection circuit like these ones do: https://uk.rs-online.com/web/p/speciality-size-rechargeable-batteries/8801558
The problem is fitting them inside as I think they're slightly longer than C battires.
Have you considered getting rechargeable C cells?: rechargeable c cells
Converting it to lithium needs to be done right if done at all, as if they're wired up wrong for charging they can be quite dangerous (though usually the protection circuitry prevents it, but it's not guaranteed).
This post was modified 3 years ago 3 times by DIY Perks
Posted : 18/01/2023 11:04 am
Topic starter
Hi DIY Perks,
Thank you for your reply.
I’ve attached some pictures - I don’t know if this is series or parallel, hoping you’ll be able to determine that from the pics.
I think you’re probably right as this toy has multiple motors, so it would need more than a 1.5v circuit and 6v makes sense in my head anyway.
Why would I need expensive batteries with voltage protection if I’m going to add a BMS thingy / circuit board with a USB charging plug on it? Like this one:
BMS (I know the voltage is wrong and there’s on USB connector, I’ll need to add that to it.)
My point is the BMS board already has voltage protection? (Not arguing, just a bit lost lol)
My thinking is I buy this or something like it, connect it between the toy and the batteries (of which I think they’ll need to be 4) or I may buy a pre-made 4 battery wrapped pack, like this one:
6v lithium ion wrapped with plug
Or I could (somehow) put together some of the Lithium ion 18650 cells I recovered from an old laptop battery that didn’t charge but all 6 of the lithium ion cells in it were 100% fine.
So, if I put two of these 18650 cells together, each are 3.7v, then I’d have a 7.2v circuit, instead of the 6v I need?
Maybe I’d need some kind of BMS board that is adjustable, so I can turn the volts down to 6v maybe?
Hint: This is where you come in! Lol
P.s. - pls don't recommend a solution using those pesky molex type plugs - I can’t see them properly anymore to crimp them, and I don’t have a pin crimper anymore lol.
I don't mind "customising" the battery bay to acommodate rechargeable cells, as I plan to cut into it elsewhere for the USB charging port (unless I end up connecting one of those pre made wires to the toy, so as I only have to unplug the battery pack to charge it up.
Yes, I did consider buying rechargeable C batteries, but this is much more about learning how, as I know there will be lots of other situations where I'll need to change the power sources of.
Take care & look forward to your solution!
Steve
Posted : 18/01/2023 7:12 pm
It would be worth testing the charger you linked to first to see if it protects any batteries connected to it from overdischarging. If it does, you're quite right, having protected 18650 batteries is not necessary. It just doesn't seem to mention it in the listing so it's always worth testing to make sure it has that functionality.
The battery compartment is indeed series by the way!
If you're worried about 7.2v (well, probably more like 8.4 when fully charged) then you could power it through a voltage step down board before it hits the toy. My guess is that 8.4v would probably be ok anyway, but no guarantees!
Other than that it seems like you have most things ready to give it a go 🙂
Posted : 19/01/2023 11:14 am
Topic starter
I think I've found the right one to do the job, but I just wanted to check with more knowledgable people than myself.
I want to use 4 x 18650 batteries, but keep a 7.4v circuit. I think if I wire 2 pairs of 2 x 18650 batteries in parallel and connect each pair in series, I'll basically have a longer lasting 7.4v battery than I would if I only used 2 x 18650 batteries, make sense?
If that's right, I'm also a bit stuck on how to wire it all up and where to put the connector (and would I buy just any old USB-C connector if this is the correct charger board to buy & use) to plug in the charging cable, which I would like to be just any old USB-C cable, that way, there's no hunting around for the right charger, just any old USB-C cable will do it.
Guidance her ewould be greatly appreciated!
Many thanks in advance,
Steve
Posted : 28/01/2023 11:43 am