My mentor gave me some old motor 269’s and some motors just labeled “MOTOR MODULE” which seem to be a servo or have an encoder or something because it’s 3 wire. Anyways he also gave me two 7.2 3000MAH NiMH batteries. I want to know if they have a built in BMS. I assume they do because there is only two wires coming out of the pack and there appears to be two cells just by feeling the pack. The main questions are, do they have a BMS built in?, do I need a special charger?, If I need a special charger why if they have a BMS (I’m assuming that the old BMS would have a charging feature like modern ones but idk), How would I charge them if I put them in parallel?
Assuming it looks like this:
There is NOT a BMS. This is a low end nimh r/c car pack consisting of 6 sub-c cells in series. You can trickle charge overnight or fast charge in ~15 mins with a r/c charger. Not sure how long the vex charger would take.
Your local hobby shop likely has some trickle chargers for old tech like that that they might give or sell you for cheap.
following what turbodog said, those batteries do NOT have a built in BMS. it’s just voltage in, voltage out. from the picture, it looks like a mini tamiya connector, and chargers for those batteries and connectors are prevalent in the r/c world.
No BMS. These batteries will happily start a fire if shorted or damaged.
Just for transparency, I’ve edited the OP for formatting purposes.
The situation would need to be exactly right. I raced r/c using these same cells for years. There were TONS of abuse dished out. I saw cells get HOT and vent, but never saw a fire. Never heard of one either.
Once r/c went to lithium cells… that’s when we saw fires during races.
If you short any high current pack, or damage it, you open the door for a fire, BMS or not.
Moral of the story: don’t drop your packs and don’t use one that’s got obvious problems. Treat them like the $100 that they cost to replace and the untold damage they can cause from a fire.
how does It charge safely and balance if there is no BMS? And If I put two in parallel do I just connect the output straight to the charger? how would the cells balance?
Ah, you youngsters… growing up in the age of BMS and lithium-based cells.
If you trickle charge it, the cells that are first to reach full charge continue to charge, bleeding off excess charge as low-level heat.
If you fast charge it (like in r/c racing) you typically build a pack from loose cells that have been rated to be exactly the same capacity… so no balancing required except for the occasional trickle charge.
I would NOT charge packs in parallel. The lower voltage one will overcharge and the higher voltage one will never reach full charge.
So can I charge them separately and them reconnect them into parallel once done charging?
It actually is just a motor. The 3 wires are power, ground and PWM signal. It has a built in motor controller.
Worlds 2014 7.2 battery combusted after battery cable sheared by lift mechanism.
You can now say you have heard of it
2014 was nimh? To nitpick, I only see smoke… which I have seen when cell covers/wiring get really hot. I’m talking flames… of which I’ve only seen after moving to lithium.
Nimh had a lot going for it… and is certainly still viable tech in the right circumstances.
take it whichever way you wish - smoke is a good indicator of chemical reaction happening, either cell level, or encapsulating level … field techs removed the robot there and stated it combusted.
Had another incident year later (I think) of battery meltdown had to kick battery out of area…
Just accept that energized systems have their perils - maybe not as dramatic as lithium ion on YouTube…
Nitpick is what we do:). end of the day, we keep students safe.