Hi !
I am building an electric cart (Just for the fun of it), got my hands on 24V 500W brushed dc motor.
I already own 6 Dewalt's 5ah 20V battery packs which I would like to use in parallel connection in order to run the motor.
(I do realize that the output power will be significantly lower than the rated output power)

My biggest concern is how to make sure I dont ruin the batteries.
I belive these batteries can deliver 5-10amps with no problem, So heating the batteries is not my first concern as the current should be no more than 21Amps in total (which is for 24V) and less than 4 amps for each battery.

Low Voltage Protection for each battery will also be used in order to make sure I dont overdrain the batteries so I think I got it of the way as well.

I am not sure about mutual currents between the battery packs, even if I fully charge all the batteries I gues voltage diffrences might develop.
Are such currents harmfull ?
I was thinking to connect a diode at the positive terminal of each battery pack in order to prevent such currents.

Here is a drawing of the electrical system.
Please let me know what you guys think!

 

As long as the voltages are the same when placed in parallel, it is OK. Once they are in parallel, a voltage difference is impossible, since they are all connected together. A few millivolts of difference is also OK, they will equalize quickly.

You should be aware that the current you have calculated is the run current. Start current may be 5X or more higher. If the battery cannot provide the start current, the motor may not start.

 

As long as the voltages are the same when placed in parallel, it is OK. Once they are in parallel, a voltage difference is impossible, since they are all connected together. A few millivolts of difference is also OK, they will equalize quickly.

You should be aware that the current you have calculated is the run current. Start current may be 5X or more higher. If the battery cannot provide the start current, the motor may not start.

I got two questions following your answer:

1.The PWM speed controller allows me to adjust the voltage between 0V-20V, So if I gradually raise the voltage, Can I assume the start current will be pretty low, like soft start ?
(maybe 2x nominal but not higher) ?

2. For the parallel connection, What if the voltage difference is more like 0.1V is it harmfull ?

3. What if I connect a small a resistor (say 1ohm) at the output of each battery?
Will it keep the mutual charging currents low ?
Thanks!

 

A 500 watt 24 volt motor will require a bit over 20 amps for the rated output.With six matched battery packs that will be a bit over three amps from each battery. And the effort to match the connections so that the load will be equal on all six batteries does not seem simple. In addition, the chance of damaging the battery packs is real.

 

20V Dewalt 5AH battery packs can deliver more than 40A each, and routinely do so when powering Dewalt tools. Consider the larger power drills, which deliver around 1000W (mechanical); that will require over 50A from the battery, which it can do, but not continuously.

Your 500W motor is not going to deliver exhilarating performance for an electric go cart. It is going to be like a "power wheels" (barbie car version). You are better off just using a Dewalt drill to power your go cart. Then all the speed control and battery protection circuits are handled for you, and it will have more power.

 

I was off by little bit. Barbie car is actually only 200W so this 24V motor will be slightly more peppy.