How much juice do these things suck on start-up?

[Electrobent]

My cruise controller arrived today and I hooked it up. 

I triple-checked everything, downloaded the Pro-Kit users guide to make sure I had not missed anything.

I hooked up the battery and flipped my switch and half a second later the 20A mini-breaker I have in series with the power switch blew.

Do I need a bigger fuse or is something wrong?

[GM Brazil]

20A?

My Magic Pie sucks 30A.... with a 48v battery. Bu I do not know your setup details, power of the motor, voltagen, etc.

[Electrobent]

48V 1000W Cruise Controller, non GM NiMH batteries

[Bikemad]

I hooked up the battery and flipped my switch and half a second later the 20A mini-breaker I have in series with the power switch blew.

Do I need a bigger fuse or is something wrong?

Eric,

The controller is rated at 50Amps and the motor will probably draw over 40 Amps under extreme load, so your 20A mini-breaker would seem to be a bit on the low side.

I have attached a graph showing some dynomometer results for a GM 1000W 48V motor.
As you can see it's drawing 37.46Amps at its maximum tested load, if it was loaded even more, then the current would be higher!

Hope this helps.

Alan
 

[Electrobent]

Looks like I guessed about right when I bought a 45A breaker.  I have two connections to solder and then I can test that.

But the 48V regen controller never flipped the 20 amper.  It flipped once riding up a hill with the 36V setup.  


45A was enough--it immediately spun up perfectly---and reverse works too!

I should have this thing all put together this weekend.

I'll report again after the first ride

[Leslie]

Yea those caps in the controllers will draw a bit of current when switched on.  Large capacitors can draw more than your motor with in a spike.  If your breaker is sensitive, problems may be intermittent.

Pre charge circuit is what I am working on now.

Just an idea.  I am using a LM317t, cap on the adjust and discharge diode to delay the voltage current surge to a relay.  The main switch switches a 1 ohm resistor to the controller and charges the caps and initiates the lm317t, takes its time, about 500 ms (depends on the cap) to induce the relay to give a true connection to the pack.

If I finish this one with success I will post my circuit.

ATM I have one relay working on the bench but I am using 2 lm317t's, one in current limitation configuration to charge a large cap to build up the voltage to the coil slowly and a another to regulate the voltage to the coil. The voltage regulator isn't needed but serves to protect the 120 ohm coil while I tinker.

The new one I am working on is in simulation ATM and looks to be superior as it requires a smaller cap on the adj that delays the voltage rise on the output to the relay.

This circuit in spice is not straight forward either, as the cap needs a discharge path when the device is switched off and the input voltage is way over the specs of the regulator, standard schematics and values tend to fail in simulation.     

[Bikemad]

The simple solution for the  pre-charge is to have a momentary push button switch and resistor across your main switch contacts.
Simply hold the button down for a second before throwing the switch and you'll get no spark at all.

If you don't have a switch, it might be easier to put another connector on your battery positive connection.
This would be wired in parallel to the Positive cable but would have the resistor fitted in-line.
You simply connect the Negative lead first, then the Resistor lead followed by the Positive lead and again no sparks!
Simple solutions may not always be the best solution, but they are usually easier and cheaper.

Here's another interesting method that I came across while searching for a solution:


This picture shows both the connectors on the motor (speed controller) side.
It uses a ½Watt 33Ohm resistor with one end connected to the controller's negative female socket and the other end left sticking out of the heatshrink.
With this method, the positive lead must be connected first, then you simply touch the sticking out part of the resistor with the battery negative plug to pre-charge the capacitors in the controller before pushing it right into the socket. (Simple but effective yet again.)

Alan