Build a radio control car battery charger

[mikesmixes]

Hey,

Does anyone know of any designs or circuits for building a fast charger for remopte control car batteries. They are 7.2V NiMh, 1700-2400mAh.

I need a fast charger for racing days. It must run off 12v car battery preferably.

Thanks.
Pat

 

[Nigel Goodwin]

Hey,

Does anyone know of any designs or circuits for building a fast charger for remopte control car batteries. They are 7.2V NiMh, 1700-2400mAh.

I need a fast charger for racing days. It must run off 12v car battery preferably.

All you really need is a low value, high wattage, resistor - which is what commercial units usually do. A timer would also be extremely useful, fast charging is already damaging your batteries enough, so you don't want to over do it!.

What charge rate do you want?.

 

[ante]

Pat,

How fast is fast in your book? C*2 ?
I made a peek detect charger for this purpose some years ago running of car battery or bench psu adjustable 0 – 5A. Are you interested?

Ante :roll:

 

[mikesmixes]

hey, thanks for the reply. yeah im interested in your peak charge detector. I need to charge in about 20-25 minutes. I know it damages the battery but "hey what can you do....?" Have you got schematics?

What "C" is around the safest for NiMh batteries? How long would 2C be, about 30min?


Are you interested in RC cars, or what did u build it for?

 

[ante]

Pat,

I built this circuit about 10 years ago when I was into RC-cars. At the time we used Ni Cads and the tracks where we used to race was sometimes not equipped with mains power. This circuit runs from a car battery or a 12 – 14 Volt PSU whichever is at hand. R1 and Q1 is not necessary if you don’t want thermal safety. I used this input connected to a temp switch NO. that closes at 40 deg C and was attached to the pack on charge. This was a safety measure if something goes wrong the charger cuts off before the pack gets fried.

Ante :roll:

 

[ante]

Pat,

I built this circuit about 10 years ago when I was into RC-cars. At the time we used Ni Cads and the tracks where we used to race was sometimes not equipped with mains power. This circuit runs from a car battery or a 12 – 14 Volt PSU whichever is at hand. R1 and Q1 is not necessary if you don’t want thermal safety. I used this input connected to a temp switch NO. that closes at 40 deg C and was attached to the pack on charge. This was a safety measure if something goes wrong the charger cuts off before the pack gets fried.

Ante :roll:

 

[mikesmixes]

hey thatnks for the circuit.

What is the max current that can be drawn from this circuit and is it suitable for charging Ni Mh batteries.

What is the best charging time for the battery on this charger? I will be using the car battery at races.

Thanks

 

[ante]

Pat,

The maximum current I have used is 5.5A but maybe 6.5A is possible. The MOSFET can be equipped with a small fan (apart from the heatsink) and there should be no problems. The charging time depends on the charging current and the capacity of the pack on charge. Can the Ni Mh cells these days be charged at this high currents? We always used Ni Cads because they could deliver much higher current to the motor and survive the fast charge abuse.


Ante :roll:

 

[mikesmixes]

I am going to mount a fan for the FET's heatsink for extra cooling. One more thing, does this charger actually go into trickle charge mode when the battery is full or does it cut-off.

If i leave out the Q1 and R1 for the temp sensor, would D1 and R2 be connectred up to your positive rail? Is the N/O thermal switch is connected to the positive rail or to ground??

 

[ante]

Pat,

The purpose of R4 is to trickle charge the pack after the main charge is finished. As you can see it is “bypassing” Q2 and is always connected to supply. If you omit R1 & Q1 don’t change anything else. If you want to use the “cut off” the temperature switch shall be connected between R1 and the positive rail. The NO switch will provide R1 with positive when desired temperature is reached. The cap C1 must be MKT type to work properly and the LED should be a green LED to have the correct voltage drop.

Ante :roll:

 

[ante]

I forgot to mark the positive rail, it’s the one on top as I am sure you can see. Supply is coming in from the left and the pack is connected to the right!

Ante :roll:

 

[mikesmixes]

hey thatnks for the info. I was asking about leaving off R1 and Q1. If I dont use them then where would ANODE of D1 be connected as with the left pin of the RV1....just wondering.

i am going to use a IRFZ48 for the mosfet just because i have a few left over, they have almost the same stats and the Rds-ON is about as low as the BUK455.

Will let you know how it is going.
cheers