# Yet another dcdc fuse blowing thread



## piotrsko (Dec 9, 2007)

first thing I'd do is to throw an ammeter on the output of the chennic then punch the throttle once in the driveway. The Sol manual states that it can dissipate up to 960 watts all by itself depending on what it is running.


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## Tesseract (Sep 27, 2008)

mk4gti said:


> My Chennic dc/dc converter, 300W, 120v keeps blowing the input fuse...
> I added a 100uH torrid Inductor coil (5A) inline with the input fuse positive side:
> ...
> DC/DC works fine at rest but fuse blows as soon as the vehicle accelerates
> ...


Another possible cause of the fuse blowing is plain old voltage sag. DC/DC converters draw a more or less constant input power so as the traction pack voltage drops they will pull more current from it. A smart DC/DC design will stop operating when the input voltage drops too low, and the fuse protecting it should be a slow-blow type rated for at least 50% more current than required at full load and low line, so to speak. So a ~5A fuse in this case, at a minimum.


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## Tesseract (Sep 27, 2008)

piotrsko said:


> first thing I'd do is to throw an ammeter on the output of the chennic then punch the throttle once in the driveway. The Sol manual states that it can dissipate up to 960 watts all by itself depending on what it is running.


Err... not quite!? Even the Shiva requires less than 50W from the 12V supply to operate! A Jr requires less than 10W. You might be referring to the losses on the high power side, though I don't recall mentioning any specific numbers for that in the manual...


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## piotrsko (Dec 9, 2007)

no, I saw somewhere that it can have an input requirement of up to 8 amps if all the 12 v controlled outputs were firing. Might be an early version of the manual. It is 4 am here, dissipate could be the wrong term.


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## mk4gti (May 6, 2011)

Tesseract said:


> Another possible cause of the fuse blowing is plain old voltage sag. DC/DC converters draw a more or less constant input power so as the traction pack voltage drops they will pull more current from it. A smart DC/DC design will stop operating when the input voltage drops too low, and the fuse protecting it should be a slow-blow type rated for at least 50% more current than required at full load and low line, so to speak. So a ~5A fuse in this case, at a minimum.


I appreciate your response Tess. Yes, with the colder weather, I have noticed more sag during hard accels (sags down 10-15V from 130V).

Although I can appreciate the fact that these DC/DC aren't the best quality, there are very common in conversions; there must be a solution!

I can try adding another inductor in series, would that help?
Would I need an inductor on the negative side?


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## Ziggythewiz (May 16, 2010)

Doesn't Jack R use a diode and an inductor as standard after dealing with these issues?


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## Tesseract (Sep 27, 2008)

piotrsko said:


> no, I saw somewhere that it can have an input requirement of up to 8 amps if all the 12 v controlled outputs were firing. Might be an early version of the manual. It is 4 am here, dissipate could be the wrong term.


That is correct - a brief pulse of 8A is required to engage each contactor. That's 96W, though, not 960W... 




mk4gti said:


> I appreciate your response Tess. Yes, with the colder weather, I have noticed more sag during hard accels (sags down 10-15V from 130V).
> 
> Although I can appreciate the fact that these DC/DC aren't the best quality, there are very common in conversions; there must be a solution!
> 
> ...


Another inductor won't help if the problem is the dc/dc is drawing too much current as a result of battery pack voltage sag... Not sure what to advise you in this case, as I am not familiar with the Chennic.

A better quality DC/DC - or using the original alternator, driven by the tailshaft on the motor - is the best solution, but the market doesn't seem willing to pay more for this admittedly unsexy device. It's not just a matter of having to compete with the ultra low (though rising) labor cost of a Chinese manufactured product, it's also that a proper design for a dc/dc in this environment is more expensive.


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## Yukon_Shane (Jul 15, 2010)

Tesseract said:


> ... but the market doesn't seem willing to pay more for this admittedly unsexy device. It's not just a matter of having to compete with the ultra low (though rising) labor cost of a Chinese manufactured product, it's also that a proper design for a dc/dc in this environment is more expensive.


Am I correct in assuming that this means you've given up on the idea of an Evnetics DC/DC converter?


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## mk4gti (May 6, 2011)

So I added a diode to the inductor and low and behold, no fuse blowup. I even tried a smaller 10 amp fuse (compared to the "stock 15A") to see if I was close to the limit, still fine.

I used a N5408, a 3A, 1000V rectifier diode. It does get a bit hot.

Can anyone confirm if this will be safe ?


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## Ziggythewiz (May 16, 2010)

Your max load is around 3A, isn't it? I'd probably go with a 5 or 10A diode if available to keep it cooler.


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## mk4gti (May 6, 2011)

Yeah 2.3A really. (300W / 130V). Perhaps a 5A would be better suited.

I think what would happen is the controller would suck in the power from the DC/DC caps (at least, that's what I read on another board).

Although I have basic electronic background, I'm wondering if a 5A diode+ 100H inductor be a safe setup?


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## Tesseract (Sep 27, 2008)

Yukon_Shane said:


> Am I correct in assuming that this means you've given up on the idea of an Evnetics DC/DC converter?


As a standalone product? Yes. I am still considering making it an option to be integrated with the charger because that turns a $500 retail standalone DC/DC into a much more palatable $300 option on the charger.




mk4gti said:


> So I added a diode to the inductor and low and behold, no fuse blowup. I even tried a smaller 10 amp fuse (compared to the "stock 15A") to see if I was close to the limit, still fine.
> 
> I used a N5408, a 3A, 1000V rectifier diode. It does get a bit hot.
> 
> Can anyone confirm if this will be safe ?


I can't confirm this is safe - that's up to Chennic to determine (and good luck getting confirmation from them...) but it sounds like voltage sag was, indeed, the problem so this is a viable solution.

Running 2.3A through a 3a diode is technically ok, but not good engineering practice. You can use two of the diodes in parallel with a small amount of resistance (e.g. - 0.1 to 0.47 ohms) in series with each to ensure they share current equally or use a bigger diode.


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## palmer_md (Jul 22, 2011)

Tesseract said:


> As a standalone product? Yes. I am still considering making it an option to be integrated with the charger because that turns a $500 retail standalone DC/DC into a much more palatable $300 option on the charger.


Bummer on the standalone, but if you offer it with a charger, that is probably still ok. I can use a better charger and just sell the one I have. Details of the charger getting announced this week at EVCCON? or is it still under development?


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## Joey (Oct 12, 2007)

mk4tdi, thanks for posting the results with the diode. This is the dc-dc I will probably use if a more robust solution is not available by the time my project needs a dc-dc.

Tesseract, $500 for a stand alone dc-dc or as an option on the charger would be a good value to me because the quality/reliability of the existing products, in this application scares me. Looking forward to hearing more about the charger.


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## mk4gti (May 6, 2011)

Joey said:


> mk4tdi, thanks for posting the results with the diode. This is the dc-dc I will probably use if a more robust solution is not available by the time my project needs a dc-dc.


I will update this thread after a few days ...
As for the diode, please don't copy me on the part number. I had it in my toolbox and decided to try it.


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## Tesseract (Sep 27, 2008)

palmer_md said:


> ...Details of the charger getting announced this week at EVCCON? or is it still under development?


The charger is still in the "exploring options" stage and I am not getting paid to develop it so I am working at a pace commensurate with that level of compensation... 




Joey said:


> ...
> Tesseract, $500 for a stand alone dc-dc or as an option on the charger would be a good value to me because the quality/reliability of the existing products, in this application scares me. Looking forward to hearing more about the charger.


Unfortunately, you are in the minority here; most people seem content to suffer the shortcomings of the available dc/dc converters in exchange for the extremely low price. How much does that 300W Chennic cost again? $99, the last time I checked... it's hard to compete with $99.


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## mk4gti (May 6, 2011)

Well, I got to work (headlights, heater, radio, controller) and fuse didn't blow. So far, so good.



Tesseract said:


> How much does that 300W Chennic cost again? $99, the last time I checked... it's hard to compete with $99.


Perhaps. I would be willing to pay more for quality. I inherited this dc/dc as part of a kit and decided to rock it. 

It does not make sense to me that you almost need to be an Electrical Engineer to install such a simple device.


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## Ziggythewiz (May 16, 2010)

mk4gti said:


> It does not make sense to me that you almost need to be an Electrical Engineer to install such a simple device.


If you're driving a home-built EV I would argue that you ARE an Electrical Engineer.


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## skooler (Mar 26, 2011)

Tesseract said:


> $500 retail standalone DC/DC


Seems perfectly reasonable to me!


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## PStechPaul (May 1, 2012)

If the diode is getting hot it is probably marginally rated for the application. You can use a bridge rectifier which can be found with 10A to 35A rating for a dollar or so, and can be easily mounted and connected with QC slip crimp terminals. An old computer power supply probably has one or more you can scavenge. The output rectifier may be a three terminal center tap type in a TO220 package and may even be Schottky which will run at half the power loss due to lower forward drop. A standard silicon diode at rated current will drop up to 1 volt so at 2.3A that's 2.3W which is a lot for a 1N5408 diode. You could mount it on a heat sink, but a larger rectifier is the way to go.

I have a bunch of these which are 2x20A 45V and cost about a dollar: http://www.mouser.com/ProductDetail...=sGAEpiMZZMuIUjt4yeP9c5NLLsTwJPGJfdwIkqPP2EA=


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## zanktwo (Mar 18, 2011)

Can one use house batt with the dc/dc


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## dtbaker (Jan 5, 2008)

the chennics seem sensitive to voltage sag, they they sag when hit with a sudden load like vac pumps coming on... I had one die in less than one year. It MIGHT have been because I was experimenting with different ways to solve sag causing headlights to blink when vac pump came on. Different story, but a little ATV aux battery did the trick.

My new project came with a 675watt dc-dc from belktronix. American made and looks bulletproof, for $325 with soft-start option. Its pretty big, and heavy, but should be trustworthy.


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## skooler (Mar 26, 2011)

FWIW I run my chennic with a 60Ah Sinopoly aux battery and an inductor on the input side.

Has worked flawlessly, my voltage hardly ever drops even with the vacuum pump and headlights on.


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## dtbaker (Jan 5, 2008)

skooler said:


> FWIW I run my chennic with a 60Ah Sinopoly aux battery and an inductor on the input side.
> 
> Has worked flawlessly, my voltage hardly ever drops even with the vacuum pump and headlights on.


reminds me to re-cap what seems to be emerging as 'best practice'. 

The dc-dc and the charger *should* have 100uH inductor on input side added if you use a Soliton controller, and won't hurt if you have Zilla or one of the other modern controllers, not required with Curtis controllers.

Aux battery really is a good idea... soaks up the spikes in load, and may give you a little time if dc-dc fails. Something as small as an ATV battery (just 3ah) seems to do the trick for about $40.

wiring your dc-dc as 'always on' is a good idea to cover the small background loads and prevent big load to recharge aux battery when you key-on. (remember to disconnect BOTH main and aux batteries for storage over a week!)


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## mk4gti (May 6, 2011)

Over a month daily use of the car and no fuse blowing up.  I think this diode / coil combo is what was needed to help with the sag and/or ripples.

Anecdote: The other day I almost got stranded. I didn't realize but the 300W dcdc will not deliver enough watts to charge the battery when the lights/radio/heating are on. The battery was below voltage for the controller to kick on. My dc/dc is wired to start when the controller is on, so it was a catch 22.

I almost had to ask a co-worker for a boost (how ironic is that?). At least I didn't need a push start


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## Siwastaja (Aug 1, 2012)

Just as a side note, $99 for a "cheap Chinese" 300W converter sounds a bit high to me... How about a AC/DC switch mode PSU? They run at about $30 for 300W on Ebay. Heck, you have the diode there already. (But, it is a bridge rectifier and designed to run from AC; with DC, only two of the diodes heat up at double average load. If this is a problem, you should bypass the rectifier altogether, and if you still need a diode, add one.)


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