For what it’s worth, you could save a bit of time and money by going with a 2S lipo pack instead of wiring an 18650 battery carrier. For example, you could get something like this pack which is already wired with a decent set of bullet connectors and a balance plug.
It doesn’t sound very safe to me to use a battery holder to power a gas car! 1/5th on top of that!
Imagine what would happen if a bump on the road causes one of the batteries to pop out of the holder while at full throttle. That’s an accident waiting to happen.
I would either use a hard case lipo pack from hobbyking, or use 18650 cells but solder them together. You have to buy tabbed cells to do that.
It’s not powering the car, only the servos. And the holder will be in a dedicated radio box, the clearance in the box won’t even allow the battery to pop out now that you mention it i will also wrap the batteries with velcro. Also the car has 3 separate fail safes.
I know it’s cheaper, but I like the idea of using 18650s and it’s a hobby so it gives me something to play with.
Also this holder is beast! I’m talking to this one guy who is pulling 30amps through it without problems.
What if the batteries move in the holder, compress the spring and momentarily open circuits on the positive side? That would cause a short loss of control.
You also need to place balancing wires unless you are going to remove the cells and charge them individually.
The only advantage I can see in favor of 18650s is the higher power density compared to HK Lipo packs.
You should also consider the fact that if your servos are rated at 7.4V, using a holder like you want will induce a lot of parasitic resistance which will reduce the torque of your servos.
That is a good point with the spring compressing. I will have to watch out for that (if it does compress the engine will cut off so it will be easy to tell and once i regain power the brakes will throw on). The only reason I plan on putting it in a holder is so I can remove and charge them individually. The servos are actually rated at lower then 7.4v… I plan on running them hot, but others do as well without problems.
I like using 18650 because they are used in my other hobbies. Ecigs, flashlights, power banks, ebikes. and I have the gear to charge them and everything. With lipo I’d have to buy a charger and worry that it is gonna catch fire in my house.
Plus I get more experience with 18650s so I can apply it to whatever else i’ll do in the future. Already learned a lot about 18650 holders, which will apply when I plan on making my own ecig mod.
It’s up to you. What you want to do is doable, but I wouldn’t do it.
If you decide not to go that way, you can get a cheap charger:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7028
It’ll do a good job and is safe as long as you plug the balance plug! You’ll also be able to measure the capacity of your cells.
Then just get a 2S hardcase pack and be careful not to overdischarge it.
Thanks for the input! I’m just doing this as a hobby to keep me occupied. Any problems and I can just abandon the idea.
That is a nice charger and not too expensive. I’ll keep that in mind if I plan on going with lipos.
The car has 4 separate fail safes now that I think about it. My radio also monitors the receiver power and cuts the engine/pulls on the brakes if the battery reaches a specified voltage. It’s pretty safe.
These cheap holders are indeed total crap, I had bought several of them on fasttech but they are very cheap and have high resistance. They are too tight and if you solder on them to make them better the plastic melts quickly.
I now use only these boxes: https://www.fasttech.com/p/1258801
They have a better quality and reasonable price.
Do you have a link to the picture in post #18, this one looks nice.
These one seems like the best you can buy 18650 Dual Battery Holder, THM, P/N1049
I’m talking to the guys on the ecig forums where it is mostly used and one guy is running 30amps through his without problems.