# DC DC help



## Travdude (May 11, 2009)

That countdown is probably the capacitors charging up. Those DC DC converters do spark a lot when you first connect them. Does it blow the fuse when you connect it?


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## Guest (Feb 7, 2011)

Never did that before? Do these need a precharge? I think I heard that they should be precharged.


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## EVfun (Mar 14, 2010)

Most DC to DC converters have some input capacitors that will spark a bit when powered up. My old Todd converter will actually take out a fuse sometimes and I don't like the pop next to my fingers when putting it in. I turn off everything on the 12v side and precharge it by bypassing the fuse holder with a 100 ohm resistor. After about 5 seconds I put the fuse in.


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## Guest (Feb 7, 2011)

I tried again and used a 150 ohm 50w resistor for precharge and even with that it just snapped crackled a popped and I did not connect it. Not sure what is going on but it is mighty strange. Odd in deed but I will keep trying. 

Pete


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## Guest (Feb 7, 2011)

?????????????


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## KiwiEV (Jul 26, 2007)

What sort of charging system do you have? A single pack charger, or the one-charger-per-battery method? 
If it's the latter, I have a theory what's causing the hard spark.


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## Guest (Feb 7, 2011)

I don't even have my charger connected yet. Single pack charger is what I will use. I remember that I had a circuit breaker on the Ghia and I just connected everything with no power. I did not have a precharge on the Synkromotive controller as it's built in and no precharger to the DC DC converter either. I connected it all then activated the circuit breaker and never once had any sparks. I will try that gain rather than trying to connect while power is on. I will connect my on/off disconnect switch which I now have but removed from the MG. I will connect it up tomorrow and then connect the DC DC up and see what happens. No power to the controller circuit boards during this testing. Should just work. 

Pete


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## Woodsmith (Jun 5, 2008)

Could it be the same problem as shown on this thread?
http://www.diyelectriccar.com/forums/showthread.php?t=53246
Something nearly faulty before could become a proper fault after being vibrated about a bit in use.


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## Travdude (May 11, 2009)

Maybe an isolation issue? Might try taking the DC DC out of the car and just connecting it to the pack alone. That would tell you if you have a bad DC to DC.


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## Guest (Feb 7, 2011)

Tried that too. Same result. Got word out to Kelly Controls.


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## cruisin (Jun 3, 2009)

What controller are you using? Some controllers like the Kelly are NOT isolated from the car 12v-. Some spark at connection when connecting a DC converter is normal. Dont use a digital Amp meter as it is not isolated either. Use solid state DC converters that are isolated and will last forever.


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## Guest (Feb 7, 2011)

Both my Kelly and synkromotive controllers are isolated as is my Kelly DC DC converter.


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## DIYguy (Sep 18, 2008)

Pete, are you running an aux battery?


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## EVfun (Mar 14, 2010)

Hey Pete, I've got an idea. First, disconnect either the positive or negative wire from the output of the converter so you can be sure there is zero output load. Then power the unit up with a 60 watt light bulb in place of the fuse. If the light bulb gets bright and stays bright there is a problem. If the light bulb gets bright and then slowly fades dim things are looking O.K. The bulb will limit input current to about 1/2 amp so if there is a problem you won't go removing traces from the circuit boards. With the unit powered up through the light bulb and with the output still disconnected measure the output voltage and see if it is right. Think of it as similar to precharging a Curtis controller.


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## Guest (Feb 8, 2011)

Can do. I normally don't run an aux battery. No load was on the dc dc. Light idea sounds great.


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## Guest (Feb 8, 2011)

Hooked up a light to the DC DC and connected the negative side and positive side in that order and then screwed in the light. Light quickly lit and went dim and out. I connected up my multimeter to the output and I get 13.5 volts out. Viola it works just fine. Before I was hooking up the positive and then connecting the negative side and getting that harsh sparking. Connected up the negative then positive this time. That was the only difference in connecting the dc dc. Working once again. Yippie. Now to clean up behind the dash. Got some wayward wires to figure out and to replace the amp and volt meter wires to properly work. 

Moving once again forward. 


Thanks for all the suggestions guys. 

Pete


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## corbin (Apr 6, 2010)

Hey Pete -- I was also having a large spark when plugging in my pack. the DC-DC converter was always on, however the 12v output was on a relay. I do have a 12v aux battery, so I didn't need it to always be on, so I wired it to the other side of my negative contactor (I have two in my system, the negative is turned on with "key on"). I know you already saw my post, but I also modified the DC-DC converter per Lee Hart's suggestion. Details for others at:

http://www.corbinstreehouse.com/blog/2011/02/plug-bug-iota-dc-dc-converter-fix/

corbin


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