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  #21  
Old 06-09-2012, 02:13 PM
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Exclamation Re: Dcdc fuse keeps blowing

The hissing sound could very likely be one of the electrolytic capacitors overheating and venting, and it may eventually fail violently. If you watch the youtube video posted by dillond666, he discovered that an unusually long screw for the cover plate had shorted to one of the capacitors.

If you apply rated voltage to the converter, it should draw no more than about 10-20 watts, or 100 mA from a 144V supply, and the case should get only barely warm. I'd also be interested to know the open circuit output voltages at a normal range of applied voltages, and also under nominal load. The manufacturer specs leave much to the imagination, and I think there are much better and less expensive options available.
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  #22  
Old 06-10-2012, 01:13 AM
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Default Re: Dcdc fuse keeps blowing

Quote:
Originally Posted by skooler View Post
Hi all,

Having a play with the dcdc at the moment.

It's also making a hissing sound after about 20 mins use.

At first I thought that it was the sinopoly cells venting but the sound is definitely the dcdc.
Sometimes switching PSUs will make noises, it's the magnetic forces inside the transformer. (often a high-pitched whining noise)

If it's more of an electrical arcing noise (like a welding set), then that's bad!

I did once have a switching PSU which made a noise - and a stink!
Turns out a caterpillar had crawled inside and got itself right across the terminals of the mains rectifier - so it fried with 300+ Vdc across it!

PSU still worked after I cleaned it....

Quote:
Originally Posted by skooler View Post
P.s. my helper has suggested it could be damp / condensation boiling inside the unit? It's changed from an electrical hissing to a boiling sound while if written this post.

Cheers,

Mike
I think I'd disconnect it before it blows up. It doesn't sound healthy...

Richard
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  #23  
Old 06-10-2012, 02:34 PM
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Lightbulb Re: Dcdc fuse keeps blowing

Hi all,

Quick update.

I cautiously left the dcdc on while working on other areas of the car. Fire extinguisher on hand!

I monitored the acc battery voltage every so often. Once it reached ~14.3v the noise gradually faded and it cooled down.

I am fairly confident that it's because the battery is near fully charged so not working as hard.

As for the fuse... I blew another! Has anybody got any suggestions for an inductor?

Cheers,

Mike
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  #24  
Old 06-10-2012, 03:12 PM
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Default Re: Dcdc fuse keeps blowing

Quote:
Originally Posted by skooler View Post
H...
As for the fuse... I blew another! Has anybody got any suggestions for an inductor?...
Had you read the thread that EVfun linked to on the first page of this thread you wouldn't be asking this now...
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  #25  
Old 06-10-2012, 03:19 PM
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Question Re: Dcdc fuse keeps blowing

What is the load on the converter while doing your testing? Can you monitor the input and output current? What is the input and output voltage with no load? Does it still get hot?

You say it may work much harder at 12V than 14V, and I assume that is the voltage on a separate battery on the output. So you are using it as a battery charger? Is it really made for that purpose? It should have some current limiting and a voltage limit so it charges the battery at a safe current and then keeps it topped off with a "float" voltage. If it's a 400W unit and it's charging a 12V battery it may put out over 30 amps, but not much more. Are you blowing a 30 amp fuse on the output? In that case it is not current regulated and you may be charging with 100 amps or more, which will pop a 30A slow-blow fuse in about 30 seconds. If you are blowing a 30 amp input fuse on a 144V supply, I suggest wearing full body armor, as that is around 10kW and a serious explosion, with shrapnel and toxic fumes, may ensue!
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  #26  
Old 06-10-2012, 03:35 PM
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Question Re: Dcdc fuse keeps blowing

Quote:
Originally Posted by Tesseract View Post
Had you read the thread that EVfun linked to on the first page of this thread you wouldn't be asking this now...
I just read part of that thread, and although I can see where the inductor should help reduce high current pulses and excess heat in capacitors not designed with low ESR, it does not make sense that it should be needed when the motor and controller are not running. If this happened while the OP was working on other parts of the car, there should be no ripple on the batteries. And I also question why there should be so much ripple on the battery pack while running. The controller should have its own inductor and low ESR capacitor on the input, and probably also a rectifier (unless it has regen back to the pack).

And also I do not understand why a DC-DC converter of this size would use a buck topology. It is rather risky because if the switching transistor or drive should fail, it would either short the primary to ground, or allow the inductor to saturate and dump the primary voltage directly into the battery on the output. Why not use a more standard push-pull topology which is inherently safer for the output?
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  #27  
Old 06-10-2012, 04:00 PM
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Default Re: Dcdc fuse keeps blowing

Quote:
Originally Posted by PStechPaul View Post
I just read part of that thread, and although I can see where the inductor should help reduce high current pulses and excess heat in capacitors not designed with low ESR, it does not make sense that it should be needed when the motor and controller are not running.
Skooler did not say whether the controller/motor was running or not.


Quote:
Originally Posted by PStechPaul View Post
And I also question why there should be so much ripple on the battery pack while running. The controller should have its own inductor and low ESR capacitor on the input, and probably also a rectifier (unless it has regen back to the pack).
The controller should have it's own inductor, huh? Do you have *any* idea what an inductor rated for 1000A and with enough inductance to matter would cost? Or how big it would be? Just to get the ripple current to +/-20% of the rated current would require 10 sets of 00K130LE Kool-Mu cores glued together, and those cost $70/pair. Oh, and there are already 3 film capacitors inside his controller that cost $68 each.

It makes no sense to add a $700 inductor (not including winding or assembly) or increase the capacitance in the controller in $68 increments just to protect a $200 dc/dc converter from the controller's ripple; especially when you can use a $5 inductor on the input to the converter to do the same.

Quote:
Originally Posted by PStechPaul View Post
And also I do not understand why a DC-DC converter of this size would use a buck topology.
The Chennic DC/DC converter doesn't use a buck topology. Where did you get the idea that it did?
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  #28  
Old 06-10-2012, 04:42 PM
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Arrow Re: Dcdc fuse keeps blowing

Quote:
Originally Posted by Tesseract View Post
Skooler did not say whether the controller/motor was running or not.
He said he was working on other parts of the car. So it seemed unlikely that it was running. It's an important part of the puzzle, anyway.

Quote:
The controller should have it's own inductor, huh? Do you have *any* idea what an inductor rated for 1000A and with enough inductance to matter would cost? Or how big it would be? Just to get the ripple current to +/-20% of the rated current would require 10 sets of 00K130LE Kool-Mu cores glued together, and those cost $70/pair. Oh, and there are already 3 film capacitors inside his controller that cost $68 each.

It makes no sense to add a $700 inductor (not including winding or assembly) or increase the capacitance in the controller in $68 increments just to protect a $200 dc/dc converter from the controller's ripple; especially when you can use a $5 inductor on the input to the converter to do the same.
I'm thinking about AC VF drives, which usually have link inductors or at least a provision for them. But this is generally to smooth the link and to reduce reflected ripple back to the AC supply, although this is generally more current ripple than voltage ripple because of the input rectifiers. DC PWM drives for BDC motors may be a totally different animal, and I'm not experienced in their design or use.

Quote:
The Chennic DC/DC converter doesn't use a buck topology. Where did you get the idea that it did?
I'm probably thinking about the Open Revolt controller in another thread, or the video of the BMW conversion project where a buck converter is described. Is there any detailed info on the Chennic? I could not find very much at all, and it was confusing that it could be used both as a battery charger and a 12V DC-DC accessory supply. No specs on line or load regulation.

Sorry if I have made any "stupid" assumptions. But there are some things about EV conversions that do not seem quite "right", and I'm trying to understand the reasons for certain problems and component choices.
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  #29  
Old 06-12-2012, 07:31 AM
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Default Re: Dcdc fuse keeps blowing

Quote:
Originally Posted by Tesseract View Post
Had you read the thread that EVfun linked to on the first page of this thread you wouldn't be asking this now...
Hi Jeffrey,

I have read it, I'll be perfectly honest - I understand why a Inductor is needed but I dont understand how to calculate its size? Or are you saying that a 100uH inductor will be suitable for most EV DCDC applications due to the minimal voltage sag? (overkill is always necessary and all that!)

To answer some other questions and clarify some points,

PStechPaul,
No load on the DCDC while testing - Except for the battery its charging. other than that its just the normal parasitic loads on the car. Im guessing it cooled down once the battery was fully charged and that load went away!

Unfortunately I have no way of measuring the current. Any recomendations on a cheap meter?

There is no fuse on the output. Just a 15/20Amp fuse on the input.

While testing nothing else on the car was 'on', the fuse only blows when the car is being driven.

Finally, it makes perfect sense to me why the controller would not protect the other components by using its own inductor. the other components should fend for themselves!

Back to my original question. What inductor is best to use?

http://www.ebay.co.uk/itm/Electronic...item2a1ebdccd4

http://www.ebay.co.uk/itm/BOURNS-PM2...item3cc2a86ebf

?????

Will a diode have any use with the inductor or should I leave it out?

Thanks again!

Cheers,

Mike
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  #30  
Old 06-12-2012, 08:00 AM
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Default Re: Dcdc fuse keeps blowing

I think you are missing the forest for the trees with all the talk about controllers diodes and inductance.... the point is that the dc-dc is working too hard, and may already be damaged by getting so hot so many times.

The big question you should answer is WHAT is the load thats blowing the fuses? Is it your aux battery (that you said got drained to 0v, right)? something else???

get an inexpensive clamp ammeter/mutimeter (like a craftsman) and track the load down!
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