Hi all,
I'm installing a 750W 36V rear hub brushless motor onto a SLA system. Once everything is connected, with the throttle control on off, I get a huge spark when I make the final connection between the controller and the batteries.
I've been reading on this forum that the spark can be considered normal, since some capacitors inside the controller are being charged for the first time.
But how do I tell between a short circuit and a normal spark? I'm a bit afraid because the spark makes a loud pop and a bright light. I have the power connector soldered from the batteries, and the other end of the connector from the controller. Do I just put the two together and hold on tight? What kind of risk is there for electrocution? =) Thanks!
a short circuit will continue to draw significant current after the spark.
if it were a short, you would also get a second spark when you break the connection.
if its just the input caps charging, the current will fall to near 0.
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Thanks Matt!
I wired in a heavy duty switch so I could break off the connection quickly if it there was a short. The fuse blew.
I am wondering if the placement of my fuse is the problem. Here's how I currently have it set up:
Would this wiring be better?:
Thank you all!
Electra Voy 88911 Community Site:
http://electravoy.blogspot.com/
Doesnt' matter how you wire the series connection, all components still see the same current rush. ;)
If you don't like the spark, you could put a switch-duty rated circuit breaker in there instead of (or in addition to) the fuse. Leave it turned off whenever you connect the pack, and then no spark will be visible because it is inside the CB.
Also, the CB will pop if it really is a short circuit but not from inrush.
If you use the CB to switch on and off, it must be rated for switch duty, and say so, or you will quickly wear it out as it seems most are only designed for a few cycles, a few dozen at best, in their lifetime (for high-voltage breakers, like on houses, anyway).
Also, make sure the CB is rated for your pack *DC* voltage at your maximum current draw, or else it may just weld itself shut trying to open up under load if something goes wrong at max current. Many breakers have a very small DC voltage they will work at, compared to the AC voltage they are rated for. Same for relays. I've already been there and done that. :(
If the fuse blows, try using a slow-blow fuse instead of a standard (fast blow) fuse. The inrush current could be very high for an instant, if there are a lot of large capacitors in the controller.
Another way around this is a "precharge resistor", which would be wired across the breaker or switch, in parallel to it, and in series with the battery-to-controller connection, so that when you plug in the battery it slows down the rate at which the caps charge up. Then after a few seconds (10-30, depending on your resistor, the voltage of your pack, and the capacitance of the controller), you throw the switch or breaker to short across the resistor and turn on your system fully. This is what car-sized EVs use.
--
Michael Elliott
Cybernetic Necromancers, Discorporated
Phoenix, AZ
Watch me build an electric-assisted recumbent bike from recycled junk:
http://electricle.blogspot.com
You had some great info in the replies. I just wanted to add a bit of color:-
short circuit == big flash, vaporized connectors, hot wires, and a big current that just keeps going
normal spark == pop, crackle, maybe a startle, and that's it
I have a collection of half-vaporized tools to prove the first definition.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
Thank you both for the great replies!
I have ordered some slow blow fuses, and a new fuse holder. I will report my findings soon!
Here's the MAXI slow blow/time delay fuses I ordered from McMaster:
I then ordered a compatible fuse holder from eBay:
Electra Voy 88911 Community Site:
http://electravoy.blogspot.com/