# DC->DC Converter keeps blowing fuses?



## Tesseract (Sep 27, 2008)

Overlander23 said:


> I've got a Chennic 500W DC->DC converter on a 205v nominal system. The vehicle doesn't use much power at all, but the Chennic's 15A input fuse keeps blowing.
> ...
> The fuse seems to blow when my traction pack demands over a certain amperage (say 70-100+), and load voltage dips to about 196v. Keep in mind that the 12v load doesn't change.


Sounds like Chennic didn't spend the extra dollars to put an inductor in series with the input (maybe that's why they are so cheap?).

20 turns on core CK610060 from this site - http://www.cwsbytemark.com/index.php?main_page=index&cPath=206_238 - will do the job. I think Rebirth Auto sells these pre-made.


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## Joe Jackman (Dec 6, 2010)

Hi Jeff (and all). This is my first post to this blog, so for what it's worth, this might help.
I think the input capacitors in the Chennic are trying to discharge suddenly when you accelerate or otherwise suddenly drawing large current from the traction pack.
A >15 amp diode in the supply line to the Chennic would prevent those caps from trying to run your car during the sudden sags.
The diode should be at least twice the sag voltage and oriented with the banded (cathode) end toward the Chennic.
Hope this helps.
Joe.


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## Tesseract (Sep 27, 2008)

Joe Jackman said:


> ...
> A >15 amp diode in the supply line to the Chennic would prevent those caps from trying to run your car during the sudden sags.


That should work, too. Less expensive than the inductor, BUT, also less effective at isolating noise/ripple from the controller making it into the dc/dc converter (which will cook the dc/dc converter's input capacitor(s) in short order).


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## cruisin (Jun 3, 2009)

This is one more reason to get rid of those so called DC converters that keep crapping out on everybody. I have never seen so many people with the same problem and dont do anything about it. The solution, a couple quarter brick SS DC converters switched on with the ignition and charging a 3 cell li-ion battery pack. This will last almost forever and never give you a problem. Also, change out all the light bulbs to LED for a very low cost and power consumption.


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## Joe Jackman (Dec 6, 2010)

Thanks Jeffrey. I just thought that because it was working okay otherwise, the diode would be acceptable. But of course, if they didn't protect the converter from sudden sags, then what else did Chennic miss. Two birds with one ...choke...
Joe.


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## Overlander23 (Jun 15, 2009)

Thanks guys! I've got three 200W Vicor bricks sitting in the wings waiting to be put together, but I had already purchased the Chennic. Cheap is definitely cheap (only about $100 for the Chennic.) If all it really takes to keep it going is a minor outlay then it's probably still worth it. The unit is certainly much nicer and seemingly robust than the IOTAs (I have a DLS-220-30 to compare it to). The contents are fully potted in a nice heat-sinked enclosure.

Chennic advertises "reverse polarity protection", which is where the fuse comes in. After I posted, I began making the connection between lowering and possibly a reversal of current under traction load and that fuse going. So a diode-type device makes sense to me.

And the inductor makes sense from a filtering standpoint. Forgive my ignorance, but how does an inductor coil prevent voltage reversal? By essentially filtering out transient reversals? Is the filter period for the inductor quite long? Or is what is needed really an inductor and a diode? Though I've learned not to actual question Tesseract's advice , btw my tach does work now, thanks for that!


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## EVfun (Mar 14, 2010)

cruisin said:


> This is one more reason to get rid of those so called DC converters that keep crapping out on everybody. I have never seen so many people with the same problem and dont do anything about it. The solution, a couple quarter brick SS DC converters switched on with the ignition and charging a 3 cell li-ion battery pack. This will last almost forever and never give you a problem. Also, change out all the light bulbs to LED for a very low cost and power consumption.


So... you are recommending to change brands of DC>DC converter? Not a bad idea, but who's bricks do you recommend? The ones I pulled when I put in a concrete walkway don't work.


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## Tesseract (Sep 27, 2008)

Overlander23 said:


> ... Forgive my ignorance, but how does an inductor coil prevent voltage reversal?...


It doesn't! Rather, the inductor and input capacitor for the converter form a low pass filter that basically averages out the ripple from the controller. In contrast, a diode will only block the voltage troughs of the ripple while letting through the peaks. That is to say, the dc/dc converter's input capacitors will still be exposed to half the ripple from the controller

The core I previously suggested is a bit large for just protecting the dc/dc converter; Rebirth Auto sells it as a means of protecting the charger, too (it can handle up to 25A of current before saturating enough to render it less effective). I especially recommend it (or something like it) if you have a Zivan carger (the Elcon's - despite being much cheaper and from China - are better engineered in this regard; go figure).


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## Overlander23 (Jun 15, 2009)

As it's the weekend... and I'm impatient, I scrounged up a 6A - 50PIV rectifier and placed it in-line to the converter, as a test. Went for a spin, hit 250 peak traction amps, and my last 15A fuse appears to still be in intact.

Hopefully I can procure the inductor sometime next week.


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## waveformblue (Jun 17, 2011)

As mentioned before, the controller motor load is discharging the DC-DC input caps. The pull is so strong that the polarity on the converter briefly reverses. This is where the "reverse polarity protection" blows the fuse. My guess is that the protection is no more than a reversed medium-current diode across the input and the 15-Amp fuse. The circuit is protected when the fuse blows. If this is the case, I wouldn't do that too often, as the diode may eventually short before the fuse opens.

Is there any way for you to connect the DC-DC directly to the battery ? If there is a remote enable line on the converter, use it. Otherwise, wire in a separate switch or relay to the converter input and call it a day.

Also mentioned above...a choke at the converter input will greatly reduce ripple induced by the controller. However, too much inductance that close to the controller's capacitor bank could introduce a different breed of gremlins.

The best place to connect the input of any DC-DC converter is across the battery.

Good luck.

~


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## Overlander23 (Jun 15, 2009)

The converter is attached directly to the traction pack and switched via an independent EV200. Well... that is to say, the traction pack is attached to the + and - input terminals of the Soliton-1, the charger and DC->DC converter are also attached to the input terminals of the Soliton-1 (the input terminals of the Soliton-1 are acting like HV power distribution posts).

The switching of the Soliton-1 happens inside the Soliton-1. The switching for the converter happens at the independent EV200. The charger is just directly attached with no switching.

I could pull the fuse for the secondary contactor, and have just the Soliton-1 power up. Or vice versa, pull the Soliton-1's ignition fuse and start just the secondary HV circuits.

If this setup is bad practice, I'd like to know. I can't imagine it would make much of a difference sourcing the converter power directly from the traction pack terminals rather than the Soliton's input terminals... aside from maybe controller noise.


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## Tesseract (Sep 27, 2008)

waveformblue said:


> ...Also mentioned above...a choke at the converter input will greatly reduce ripple induced by the controller. However, too much inductance that close to the controller's capacitor bank could introduce a different breed of gremlins.
> 
> The best place to connect the input of any DC-DC converter is across the battery.


Correct; not so much; correct. In that order... 

The "not so much" is because the whole point of the controller's input capacitor is to minimize the effect of stray (or intentional) inductance in the battery circuit. The inductor I specified for Rebirth Auto to sell is approximately 100uH with sufficient amp-turns to support 20-25A of DC current flow without saturating too much.




Overlander23 said:


> ...the charger and DC->DC converter are also attached to the input terminals of the Soliton-1 (the input terminals of the Soliton-1 are acting like HV power distribution posts).
> ...
> If this setup is bad practice, I'd like to know. I can't imagine it would make much of a difference sourcing the converter power directly from the traction pack terminals rather than the Soliton's input terminals... aside from maybe controller noise.


This setup wouldn't be bad practice IF the charger and dc/dc converter manufacturers all realized that the batteries they are connecting to aren't perfect DC voltage sources - the controller can cause the battery voltage to swing wildly with current demand (ie - voltage drop across the pack's total resistance) as well as from its switching (ie - the ripple). It's not unusual to see a 2:1 swing in pack voltage at the controller's battery terminals as a result. You can certainly design dc/dc converters to tolerate this type of abuse but that's the key point: you have to design them for it! 

Anyway, the fuse on the Chennic dc/dc keeps blowing because the AC ripple from the controller is flowing through its input capacitor. If, say, the input capacitor is 100uF (typical for this size dc/dc) then it will have a reactance of 200 milliohms at 8kHz. A typical amount of AC ripple voltage from the controller's operation is 25Vpp, in the form of a sawtooth riding "on top" of the DC pack voltage. This will result in 50App (or 29Arms) of AC current to flow through a capacitor that is unlikely to be rated for more than 1Arms of ripple. No wonder these things blow up so often, eh?

The rectifier is a good solution for the dc/dc but it won't help the charger (indeed, most "smart" chargers won't function properly if you put a rectifier in series with their output because they won't detect the pack voltage on startup). The inductor works in all situations, but it is more expensive. That said, it's virtually impossible to damage it, which is certainly not true of the diode


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## Overlander23 (Jun 15, 2009)

Jeff, you mentioned before that the Elcon chargers were a little more robust than Zivans. Seeing as I have an Elcon, is the ripple issue something I'll have to worry about? 

Would it make sense to put a relay in-line with the charger outputs to physically disconnect it from the HV circuit while the ignition switch is on? This, of course, would only allow charging with the ignition off.

Using the Googleator, I came across one of your posts on the EVDL regarding the use of inductors for DC/DC converter applications and chargers. It was mentioned that the cabling between the controller and the pack acts as an inductor, but you caveated that it's hard to know for sure considering the specifics of a particular configuration/layout.

As I only have, maybe, three feet of 2/0 cabling between my pack and controller, would relocating the charger and converter leads away from the controller terminals be of much help?

Sorry for all the questions, but this kind of tech info in the DIY community really doesn't seem to be very prevalent. You get tons of info on building a basic system, talk of calculations for power consumption, etc... but almost nothing regarding the details of noise, ripple current, effects on "underbuilt" components prevalent within the DIY community, etc.

I think this info is invaluable. Thanks again!


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## Tesseract (Sep 27, 2008)

Overlander23 said:


> Jeff, you mentioned before that the Elcon chargers were a little more robust than Zivans. Seeing as I have an Elcon, is the ripple issue something I'll have to worry about?


My off-the-cuff, highly informal analysis is that the Elcon is better in this regard, yes, and this has also been borne out in Rebirth Auto's experience (Evnetics, obviously, has nothing to do with Elcon, Zivan, etc.).



Overlander23 said:


> Would it make sense to put a relay in-line with the charger outputs to physically disconnect it from the HV circuit while the ignition switch is on? This, of course, would only allow charging with the ignition off.


Sure, and this can be done in lieu of an inductor for the charger, too. Personally, I also like to use a separate set of contacts on the relay to block power to the controller whenever the charger is plugged into the pack as well.



Overlander23 said:


> As I only have, maybe, three feet of 2/0 cabling between my pack and controller, would relocating the charger and converter leads away from the controller terminals be of much help?


Unlikely, especially if the + and - cables are side by side over some/all of the run from pack to controller as that reduces the inductance. 

BTW - the inductance of a conductor in free space is approx. 20nH/in. so 3' of cable should be about 0.7uH. At 8kHz that will exhibit a reactance of 0.032 ohms. So... more or less inconsequential.


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## GizmoEV (Nov 28, 2009)

Tesseract said:


> My off-the-cuff, highly informal analysis is that the Elcon is better in this regard, yes, and this has also been borne out in Rebirth Auto's experience (Evnetics, obviously, has nothing to do with Elcon, Zivan, etc.).


So when will you be coming out with a charger and DC-DC converter? I can imagine that the setup of the charger would be quite easy for the user to do if it is anything like the setup in your controllers.

Thank you for your valuable input.


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## makesimple163com (May 27, 2011)

I design DC-DC converters.Improper design or application could cause the DC-DC converter to be instable,which you cannot judged whether your loads work or not. The output voltage may ocsillate within some range and input current is irregular.Too much input inductor is harmful.I do not know how you install the converter.Power wires from battery to input teminal of the converter may equal to some inductance. Putting some Aluminum electrolytic capacitor as close as possible to the input and output terminal of the converter is helpful.So be careful to the converter manufacture's application note or instruction manual.


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## brainzel (Jun 15, 2009)

I have to dig out these thread, because I got an urgent problem.

I had to change my controller (Curtis 1231C to Evnetics Soliton Jr.).
Wired up everything yesterday, took a ride and everything looked good.

After that I changed two parameters at the soliton:
Mode from "quiet" to "performance"
slew rate from "300A/s" to "500A/s"

Now my DC-DC converter (Chennic 400W) fuse (15A) blows everytime I accelerate (tried about ten times) :-/

I read about the ripple noise, rectifier and diodes in some threads here but don't know at least what I should do.
So here are my options / questions:

1) 10A diode inline the input wire?
2) 100uH inductor at input?
3) 10A rectifier at input?

If yes, yes, yes, which parts would you recommend?

Michael


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## Tesseract (Sep 27, 2008)

brainzel said:


> ...
> I read about the ripple noise, rectifier and diodes in some threads here but don't know at least what I should do....


This is covered on the FAQ page of our website. Scroll down to the last entry...

I even specify a couple of inductor part numbers in that FAQ entry.


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## brainzel (Jun 15, 2009)

Thanks Jeff.
I read this before but thought about your comment, that Chennic is not well known to you so it might be another problem.
If you think the 100uH inductor would be the peacemaker, I buy it immediately 

So no diodes or rectifier needed, only inductor.


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## Overlander23 (Jun 15, 2009)

brainzel said:


> Thanks Jeff.
> So no diodes or rectifier needed, only inductor.


I had a diode/rectifier on my Chennic which spawned this thread. It worked at blocking the negative spikes that were blowing the input fuse. Then I replaced it with an inductor because Tesseract know what he's talking about, and it also works... obviously. And that took care of negative spikes and ripple to the Chennic.

So yes, only the inductor needed.


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## brainzel (Jun 15, 2009)

Thanks for reply.
I ordered a 100µH inductor yesterday so I have to wait some days to test it.

I also changed the two parameters back yesterday.
Mode from to "performance" to"quiet"
slew rate from "500A/s" to "200A/s"
But that doesn't work. Fuse still blown up.

Today I took three diodes in parallel (1N5404) and wired them quick and dirty into the input wire, as a quick fix.
It works so far.


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## Tesseract (Sep 27, 2008)

brainzel said:


> ..
> I ordered a 100µH inductor yesterday so I have to wait some days to test it.


That looks like a good choice of inductor. And see how little it costs, even at single piece retail pricing? Now ask why the manufacturer of the dc/dc converter couldn't be bothered to put one inside the box...


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## brainzel (Jun 15, 2009)

Quick reply: I got my ordered 100µH 5A inductor (Toroidal choke), removed the diodes and assembled only the choke to see if it works like recommended.
And yes, *it works*.

I'll build in a 10A version in a waterproof box later to prevent saturation at higher temperatures.


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## pvgoutham (Jul 13, 2011)

Hi,

I may also facing the fuse blow out issue.
This happens as soon as I connect DC-DC to the pack, and the key is not on, so there is no potential at the thin yellow wire that is connected via the Key switch.

Any help would be useful.


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## Overlander23 (Jun 15, 2009)

Check the polarity. If it's incorrect the fuse will blow immediately.


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## Ken-Revolt (Jul 8, 2012)

This ol' mechanical engineer has looked for a *schematic* showing where the inductor should be placed to prevent DC-DC converter issues. Anyone got one or willing to sketch on Evnetics schematic and then scan it and post it?

Also, I haven't found a picture showing how to mechanically assemble and secure for a robust installation. Any hints, URL's, or tips would be appreciated.

Thanks in advance for your help!


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## chardricketts (Aug 17, 2014)

A DC to DC converter consists of an oscillator and switching transistors to convert the DC source into a alternating current. The AC is applied to the primary winding of a transformer, and diodes are used to rectify the AC from the secondary winding and the resulting DC is filtered to remove noise. Pease check the oscillator.


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## MrZion (May 4, 2016)

Hello everyone,

Sorry to revive this thread 100 years later but, I was hoping someone could explain in-depth how acceleration is exactly effecting the dc/dc converter. I understand that the motor controller will now draw more current which reflects in voltage sag at the battery pack, but if someone can take if from there that would be perfect! Please in your answer go through what has been discussed earlier such as voltage sag, voltage ripple etc.

Cheers!


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## Tesseract (Sep 27, 2008)

MrZion said:


> Hello everyone,
> 
> Sorry to revive this thread 100 years later but, I was hoping someone could explain in-depth how acceleration is exactly effecting the dc/dc converter....


I already explained this... multiple times across multiple threads. Essentially, motor controllers draw rectangular pulses of current from the battery which their internal DC link capacitors only partially integrate (smooth out) into a sawtooth shape. This variation in current causes a variation in battery pack voltage - particularly right at the controller's battery input terminals - and that ripple voltage can cause AC current to flow in any other capacitors that might be present (like those inside a DC/DC converter or a charger).

When you accelerate the controller draws ever larger pulses of current from the battery pack so the peak-to-peak value of the ripple increases. Simple as that.


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