# Kelly HWZ DC/DC Converter blowing fuses



## skooler (Mar 26, 2011)

This is quite often caused by excessive voltage sag. Basically the input caps on your dcdc become a better source if power for your controller than the battery pack - The fuse blows on the input because of power coming back out of the dcdc.

The solution is to fit a diode and a toroidal inductor on the input to the dcdc - or sove the sag issue.

Evnetics have a good writup:

http://www.evnetics.com/support/faq/


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## Andrew Burns (Mar 16, 2011)

Skooler, Thanks for your help, now that I've had a search around for the word "Inductor" I've found a lot of the threads you've described. I've been thinking that the fuse must be on the output side of the DCDC converter because it had such a high rating but it does actually make sense for it to be on the input side. I guess they just chucked a 20A fuse on there instead of ~2A it should actually draw because it's a fast-blow fuse instead of slow-blow and there is probably a decent inrush on startup.

I'll give the inductor and diode a go and fit a lower rated slow-blow fuse instead of the fast-blow one, hopefully that solves my issues.


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