I was cleaning up my “general electronics” drawer where I keep wires, motors and other misc stuff and I found a 9.6v NiCd battery and charger from an old old RC car I had 3/4 years ago. I don’t know the mAh rating on the battery or any ratings of the charger other than its input/output voltage/current.
I was wondering two things really but the main thing is: Would it be safe for me and the battery to use this 9.6v NiCd charger on a 6/7.2v lynxmotion battery?
Second question is: Could I be able to use this 9.6v battery (its got the same type of connecter as lynxmotion batteries and the wire harness) but only charge it upto 7.2v?
Oh, and I lied. Theres a third question. If I could be able to use the 9.6v battery but charged only to 6/7.2v, is there a cheap but quality way of limiting the battery to charge only upto 6/7.2v? Or like a time switch where the switch turns off after x time goes by?
I seen these sorts of things built into battery chargers that you can buy for like 30-60$ (like the hitec charger for example). I was just wondering if its possible to build your own one.
Also, if it is not suggested for me to use the 9.6v battery and charge it only upto 6/7.2v, you guys thing I should cut off the connector? It is a male connector which mates perfectly with the wire harness from lynxmotion.
Hmm… I left my 9.6v battery in the charger for like 2-3 hours and it went upto 11v and after waiting an hour it went down to 10.6v and has stayed at 10.6v since then. I check it with multimeter every day.
I wouldn’t recommend doing it.
Overcharging the battery, or charging it too quickly will damage the cells.
With NiMh, it’s pretty safe to do that (you’re house probably won’t burn down from a bit of overcharging), but damaged cells will have a greatly reduced capacity.
If you’re going to bother buying quality packs from LM, then you might as well buy a quality charger and power supply.
That’s just my opinion, though…
As for ways to lower the charging voltage to suit 7.2V chemistries, it can be done.
But, I’m not sure if just lowering the voltage will make the charger suitable.
I suppose the easiest way would be to throw some large-current diodes in series with one of the charger’s output wires.
Using your volt meter, you can start stringing diodes together until you get a drop of around 2V.
Make sure that the diodes can carry enough current.
This charger’s output is 11.6v @ 165ma. The current is A LOT lower than other battery chargers I seen. Most chargers are .6-4A. So, pretend you have a dead battery (0v or something very low) that was originally 9.6v… and you charge the battery and have a multimeter measure the voltage of the battery and then unplug the battery when it gets to 6 or 7.2v. Isn’t it safe to use?
And, I am not talking about limiting the amount of voltage that goes into the battery from the charger. I am saying that this “device” that will be added in, will stop the flow of current/electricity when it senses that the battery has been charged to 6/7.2v OR will automatically shut off the flow of current after some amount of time (Say 1 or 2 hours). Would any of those two be possible?
Wait, does lowering the output voltage of a charger decrease the amount that a battery can be charged to? So, if you decrease the output voltage to 6 or 7.2v then the battery can get charged only to 6/7.2v?
Hmm…
That’s a lot more than I’d assumed, probably too much to bother burning off with diodes.
As for cutting it off at a certain point…
It’s doable.
Off the top of my head… you could use a micro with an ADC.
If you place a voltage divider (of two equal-valued resistors in series) across the battery terminals and use a micro to read the voltage drop across one.
Then the micro multiplies that value by two to find the true voltage of the pack.
When the pack reaches the proper voltage, the micro opens the charging circuit using a transistor.
You’ll want to make that voltage divider with high-valued resistors (100k or greater sounds good to me) since you want the current that it’ll be stealing from the batteries to be as minimal as possible.
And, you might want to have that voltage divider controlled by the micro through the same transistor that controls the charging.
That way, you don’t have the resistors robbing the battery of power when the charger isn’t charging the batts.
There might be similar ways to employ this with a non-programmed digital circuit (maybe opamps?) or an analog circuit.
I think using a micro sounds like a better idea, though.
You’ve got your Atom onboard, anyhow, so you might as well use it to monitor the batts.
This’ll come in handy later, since you’ll be able to have your bot monitor it’s batteries and go charge itself autonomously when they’re low.
Do you think I could put one of these: On-Board Battery Checker inbetween the charger and battery? This way I can visually see when the battery is charged at 6v or 7.2v and unplug it myself.
I don’t want to use my basic atom because I don’t want to risk it being blown up and also don’t want to remove the ABB from the SES electronics holder. Buying a basic stamp would be pointless because I could buy charger for that price, and buying a PIC wouldn’t be a good idea since I know nothing about them or how to use them. Plus the programmer would cost 50$ in which case I could just buy a charger
