# failure of Chennic dc-dc ?



## mizlplix (May 1, 2011)

I have seen them go open mostly, but,,,hey it is possible. I would be looking/checking for a ground-to-chassis for the traction pack through the DC-DC.

But blowing both fuzes is a hint.

Unbolt the DC-DC from the chassis. set it on a non-conductor to isolate the box. Put in both fuzes. Did it blow them.

If no, then it would seem it has a component shorted to ground internally.

Pack off....VTOM one fuze holder at a time. from the DC/DC side. Holder to DC/DC box for continuity.

Maybe if you carefully inspected it and did a spot repair, it would work again?

Miz


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## dtbaker (Jan 5, 2008)

mizlplix said:


> I have seen them go open mostly, but,,,hey it is possible. I would be looking/checking for a ground-to-chassis for the traction pack through the DC-DC.
> 
> But blowing both fuzes is a hint.


both fuses blew again after I disconnected DC-DC out...




mizlplix said:


> Unbolt the DC-DC from the chassis. set it on a non-conductor to isolate the box. Put in both fuzes. Did it blow them.


dc-dc is mounted on plastic....


I will be digging into this tomorrow I hope.


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## Roy Von Rogers (Mar 21, 2009)

dtbaker said:


> both fuses blew again after I disconnected DC-DC out...
> 
> 
> 
> ...


Why keep putting fuses in, ohm the input, it will tell real quick.

Roy


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## dtbaker (Jan 5, 2008)

Roy Von Rogers said:


> Why keep putting fuses in, ohm the input, it will tell real quick.
> 
> Roy



I did not have multi-meter in car in parking lot where it died.... had spare fuses so I tried one shot to narrow it down. got car towed home and hope to dig in tomorrow.


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## Roy Von Rogers (Mar 21, 2009)

dtbaker said:


> I did not have multi-meter in car in parking lot where it died.... had spare fuses so I tried one shot to narrow it down. got car towed home and hope to dig in tomorrow.


 
I was wondering ...lol

Dont you have an aux battery ??

Roy


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## dtbaker (Jan 5, 2008)

Roy Von Rogers said:


> I was wondering ...lol
> 
> Dont you have an aux battery ??
> 
> Roy


I do not use an aux batt... dc-dc is 'always on'. 

I had a tiny battery,and then switched to a big capacitor in attempt to eliminate headlight blink when vacuum pump comes on.... I am thinking that if that capacitor got too depleted, the inrush to refill it MAY blow fuses. May go back to a slightly larger batter. I really don't have room for a big one gracefully anywhere under the hood.

I plan to disconnect everything, test dc-dc for internal short, and re-connect one item at a time....


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## Ziggythewiz (May 16, 2010)

There's always the lithium mini AUX batt approach. If supported by the DC-DC anyway, it shouldn't take much at all.


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## Roy Von Rogers (Mar 21, 2009)

Unless you hook a celllog to a lithium aux battery to keep it from totally discharging itself, I wouldnt use a lithium for such task.

Roy


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## dtbaker (Jan 5, 2008)

ok, turns out that the input side of the Chennic dc-dc was indeed shorted... kind of a bummer since it has only been in use for about 1 year. Luckily I had another one sitting on the shelf waiting for my next build. I popped it in, and appear to be back in business.

I would love to figure out if this was a freak death, or a result of cheap components, bad design, and whether I should expect much longer life from a more expensive unit like an Elcon or something else? I really don't like the fact that this failure happened when the car was basically 'just sitting' in a parking lot while I was in shopping, not even under load!

So, I took the top cover off to see if I could see anything burnt up... really cant since everything is 100% potted. For comparison, I also took a picture of the brand new one.... which looks slightly different, but not drastically.

Any ideas on what can cause a failure like this?

Any comments on whether an Elcon or something else would be worth paying a lot more for to get longer life?


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## palmer_md (Jul 22, 2011)

dtbaker said:


> Any comments on whether an Elcon or something else would be worth paying a lot more for to get longer life?


I'm awaiting the Evnetics DC-DC. I hope it surfaces soon.


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## dtbaker (Jan 5, 2008)

palmer_md said:


> I'm awaiting the Evnetics DC-DC. I hope it surfaces soon.



It sure would be slick if the Solitons had a built-in 13.8v output rated up to 500 watts! That plus the built in contactor would be a big plus over competition.

back to reality TODAY though.... any comments?


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## Coulomb (Apr 22, 2009)

dtbaker said:


> back to reality TODAY though.... any comments?


Well, those screws look like they're holding two switching transistors to a heatsink. Is it possible to get to the other side of the board, where the transistor leads come out? I'm guessing that a likely failure mode would be shorting of those transistors, collector to emitter or drain to source.

Failing that, it seems to me you have to figure a way of melting or dissolving away the potting compound. I've only ever dug away the soft silicone-like potting, that that's a PITA.

Any experts out there on de-potting? Seems like it would be a handy skill for an EVer, or at least for the community to have one or two experts at.


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## dtbaker (Jan 5, 2008)

I don't think I will be taking this thing apart... I'm not THAT curious. 

I will note however that after further reading, I may have shortened its life by choosing a nominal voltage one step below my system nominal. I did this thinking that I wanted the dc-dc to not 'brown out' when voltage sag under load brought the nominal system voltage in down. In retrospect I think the Chennic design may be too sensitive to the over-voltage at end of charge (even though there was no real load), and the cycling up to the top of its rated voltage during charge cycles may have been hard on it.

Second issue that MAY have been hard, but I don't know, was the time I had tried a large capacitor (1F stereo cap) in parallel to reduce headlight 'blink' when vacuum pump fired up at night. Perhaps the quick response and then equally quick recharge of the cap was too much for the dc-dc. On that front I have replaced with a 3ah battery, so we'll see if the replacement Chennic behaves better.

...next dc-dc will probably be a higher capacity one like the ACME available at EvoleElectrics


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