Re: Another EV bike :)
Posted: Mon Jan 27, 2014 2:33 pm
The welder took shape (of sorts) this weekend.
In the photo, the capacitor is the large aluminium piece over on the right. On the breadboard are 3 IGBT's (2 connected) on the right. The large resistor is a 200W 2R5 resistor for charging/discharging the capacitor through, to achieve the correct weld voltage in the range 0-24V.
The board with the lcd is the control board, which controls the pulse output to the IGBT drivers, and a power supply at the back left, supplying, 5V,15V and 24V.
I got the thing working and started doing some test welds. The capacitor earth was connected via a 100Amp car jump lead as opposed to bolting it in place because it gives me a quick safety disconnect point. A few test welds with this setup and everything seemed to be working fine, the scope shoed the IGBTs were switching cleanly and quickly, so i replaced the jump lead with some very heavy gauge cable.
A few test welds and I hadn't quite got as far into setting the variables as needed, when first one and then the other IGBT blew.
A 165F capacitor at 24V such as this can dump so much current , that I guess my 10mS pulse duration allowed the current to exceed the maximum of the IGBT's.
I'm a bit stuck now. I don't want to blow a small fortune on 4 or 5 IGBT's, but I want to weld these cells up, so maybe my best bet now is to look on eBay for a suitable welder which can be modified, used, and then returned to standard trim for resale afterwards.
The small 70Amp MIG welder I have here justr isn't powerful enough and acts like a resistance welder, heating the tabbing strip quickly to a cherry red colour, but, I suspect it would be just too hot for the lithium cells.
It's possible that I could go down the route of a much smaller capacitor, of 2F at 15V, but then that is more expense which will return nothing back to me afterwards.
It's time to start Googling again !
In the photo, the capacitor is the large aluminium piece over on the right. On the breadboard are 3 IGBT's (2 connected) on the right. The large resistor is a 200W 2R5 resistor for charging/discharging the capacitor through, to achieve the correct weld voltage in the range 0-24V.
The board with the lcd is the control board, which controls the pulse output to the IGBT drivers, and a power supply at the back left, supplying, 5V,15V and 24V.
I got the thing working and started doing some test welds. The capacitor earth was connected via a 100Amp car jump lead as opposed to bolting it in place because it gives me a quick safety disconnect point. A few test welds with this setup and everything seemed to be working fine, the scope shoed the IGBTs were switching cleanly and quickly, so i replaced the jump lead with some very heavy gauge cable.
A few test welds and I hadn't quite got as far into setting the variables as needed, when first one and then the other IGBT blew.
A 165F capacitor at 24V such as this can dump so much current , that I guess my 10mS pulse duration allowed the current to exceed the maximum of the IGBT's.
I'm a bit stuck now. I don't want to blow a small fortune on 4 or 5 IGBT's, but I want to weld these cells up, so maybe my best bet now is to look on eBay for a suitable welder which can be modified, used, and then returned to standard trim for resale afterwards.
The small 70Amp MIG welder I have here justr isn't powerful enough and acts like a resistance welder, heating the tabbing strip quickly to a cherry red colour, but, I suspect it would be just too hot for the lithium cells.
It's possible that I could go down the route of a much smaller capacitor, of 2F at 15V, but then that is more expense which will return nothing back to me afterwards.
It's time to start Googling again !