DIY Open Source EV Charger

[jackbauer]

Not trying to be smart but whats wrong with a transformer / rectifier charger? Having a transformer made up with a suitable secondary voltage to suit whatever pack voltage is not very expensive. All that is needed then is a simple circuit that looks at the pack voltage and drops out the charger at a certain point.

[lhogberg]

Originally Posted by adamj12b

I hate to be a bearer of bad news, but using the controller as a charger as well is very dangerous.

Of course using a controller as a charger is nothing but dumb! (edit: OK, I'm exaggerating, but the cost of extra contactors would probably be greater than the savings) My idea was just to place the charger in the same case and on the same heat sink as a controller, and since the battery-capacitors are allready there, more won't be needed.

This saves money, weight and space

[lhogberg]

Originally Posted by jackbauer

Not trying to be smart but whats wrong with a transformer / rectifier charger? Having a transformer made up with a suitable secondary voltage to suit whatever pack voltage is not very expensive. All that is needed then is a simple circuit that looks at the pack voltage and drops out the charger at a certain point.

Since the grid voltage is varying quite a lot, the charger voltage will vary as well and can be over gas voltage. Also a transformer of this size, is very heavy and expensive.

[sawickm]

Adam,

In order to use the controller as a charger, you would need to rewire the battery from the battery side to the motor side, you would then need to apply some kind of DC power to the battery side of the controller. This would require some large contactors to be able to switch back and fourth.

The controller outputs are BM+, B-, M-, what do you mean by re-wiring the batteries and motor? Do you mean isolate the batteries from the motor using larger contactors? Does that mean you could not share the busbars of the controller between the motor and charger?

A better idea, I think, to keep things cheep would to use a power stage that is only 1/5 of the drive controller. This would be 2 MOSFET/diode pairs, capable of 50A.

Could a separate charger PCB containing the (MOSFETs/diodes/charger controller) bolt on to the Revolt’s busbars, heatsink, and use the same enclosure?

-Mark

[jackbauer]

As long as the transformer was designed for a slightly less than full charging voltage and incorporated a simple overvoltage protection circuit i don't see a problem beyond the weight. I'm leaning towards having two taps on the primary that will let me do a fast charge then drop to a float charge. Much as i like the idea of a switchmode charger it doesn't provide isolation unless designed around an almost impossible to source custom hf transformer.

[lhogberg]

Originally Posted by jackbauer

As long as the transformer was designed for a slightly less than full charging voltage and incorporated a simple overvoltage protection circuit i don't see a problem beyond the weight. I'm leaning towards having two taps on the primary that will let me do a fast charge then drop to a float charge. Much as i like the idea of a switchmode charger it doesn't provide isolation unless designed around an almost impossible to source custom hf transformer.

Don't forget that maximum charging voltage has a quite strong temperature dependence. The higher the temperature the lower is the maximum charging voltage (i.e. gas voltage).

[jackbauer]

Fair point. Just looking at some easy options.

[MPaulHolmes]

instead of a transformer to get you to a rectified voltage of like 300 or something, you could just do a voltage doubler with 2 caps and 2 diodes. It wouldn't be isolated. Is that bad? hehe.

[jackbauer]

I'm not sure about the whole isolation issue. My thinking is that the car body should be connected to mains earth while charging.

[MPaulHolmes]

That would let you leave out a 25 pound transformer from the design.