[skooler]

Hi all,

The fuse on my 400w Chennic Dcdc converter is blowing every time I accelerate.

I'm running a 144v 125ah LA pack and soliton Jr limited to 600A and 80v (motor side)

The fuse that came with the converter was a 15A slow blow. I have since twice replaced it with 20A slow blows and keep melting them.

I assume that the dcdc's input caps are trying to drive the car?

M6 bolt?

Any ideas?

Cheers,

Mike

[rwaudio]

I believe that Jack R's solution on EVTV with the same problem was a diode, simply keep the current from feeding back from the dc/dc to the pack under acceleration.

Make sure you find one of suitable voltage/current.

Something like this might do the trick
http://www.ebay.co.uk/itm/DC-Power-S...ht_1693wt_1396

If using a diode that was intended to be a rectifier the current must be derated for DC use, since as a rectifier it would only conduct 50% of the time.

[PStechPaul]

The stud mount diode is rather hard to deal with. You can use a 35A 1kV bridge rectifier, and you can parallel two of the internal diodes for a total of 70 amp capacity (although best not to count on more than 50A because of uneven current sharing). Here is one for less than $4:
http://www.newark.com/fairchild-semi...-qc/dp/18C6691
And the specs:
http://www.fairchildsemi.com/ds/GB/GBPC1506.pdf

You should run separate leads from each AC leg to the battery, to help equalize the current. It needs to be bolted to a good heat sink, as the forward drop may be as high as 1.4V at 30 amps which is almost 45 watts.

[EVfun]

You need to put in inductor in series with the input to the DC to DC Converter to keep the converters input capacitance from trying to smooth ripple on the DC pack. Tesseract explains it to me starting about here.

[skooler]

Hi all,

I thought a diode would be the answer, surely it would only need to be 30 amps though? .

What really annoys me is that is is advertised for use in EVs yet isn't actually fit for purpose! Grrrrr!

Anyway. U just popped another fuse in. The main pack is currently charging for the first time so I thought I'd get some juice into the accessory battery.

The dcdc has been running for about 45 mins and is too hot to touch. It is mounted on an aluminium sheet, the bonnet (hood) is open and it has plenty of air to circulate.

Its hot enough to make some insulation tape on a nearby cable feel takky.

Is this anything to worry about?

- must admit that I'm not impressed by it so far. Hopefully evnetics can build me a nice one for under $500 ;-)

[dtbaker]

Originally Posted by skooler

Hi all,

The fuse on my 400w Chennic Dcdc converter is blowing every time I accelerate.

I'm running a 144v 125ah LA pack and soliton Jr limited to 600A and 80v (motor side)

The fuse that came with the converter was a 15A slow blow. I have since twice replaced it with 20A slow blows and keep melting them.

doesnt sound normal at all.... either there is a big load on it, or it is not handling the voltage drop on the input side when you sag under load. I found the chennic sensitive to the nominal voltage matching design nominal, so if you have a mismatch and/or massive voltage sag under load, the chennic will not be happy.

is the dc-dc 'always on' ?
have you identified ay 'significant' loads when EV is off, on but just sitting?
what kind of sag are you seeing in pack voltage under load?
do you have any aux-battery in parallel w/ dc-dc? if so are you SURE the aux battery is in decent condition and not drawing huge load to re-charge, or shorted, or....?

[skooler]

Originally Posted by dtbaker

doesnt sound normal at all.... either there is a big load on it, or it is not handling the voltage drop on the input side when you sag under load. I found the chennic sensitive to the nominal voltage matching design nominal, so if you have a mismatch and/or massive voltage sag under load, the chennic will not be happy.

is the dc-dc 'always on' ?
have you identified ay 'significant' loads when EV is off, on but just sitting?
what kind of sag are you seeing in pack voltage under load?
do you have any aux-battery in parallel we/ dc-dc? if so are you SURE the aux battery is in decent condition and not drawing huge load to re-charge, or shorted, or....?

Hi Dan,

The DCDC is wired into a contactor. The plan is to have it so that it comes on during charging and while driving.

I have had it running while 'testing' (playing) and I turned it on while the car was charging earlier to top up the acc battery.

There are no significant loads with the car off.

I am using 4 Sinopoly 60AH (B) cells as my accessory battery. It is brand new but...

I had an issue with a parasitic load when I first installed the battery and it went completely flat. all cells were below 1v, one wouldnt register a voltage on my meter. I managed to get all of them back to life and holding a charge so I dont think that its an issue

Sag is about 110V at 600A. from 150ish (not bad with LA!)

I tried running without the acc battery. The only thing the dcdc was powering was the soliton and it cut out with a 12v too low error every time I stamped on the pedal.

Im starting to think the issue is just the fact that its not a very good piece of kit.

It definately shouldnt be getting too hot to touch!


Cheers

Mike

[Yukon_Shane]

Originally Posted by skooler

Hi Dan,

The DCDC is wired into a contactor. The plan is to have it so that it comes on during charging and while driving.

I have had it running while 'testing' (playing) and I turned it on while the car was charging earlier to top up the acc battery.

There are no significant loads with the car off.

I am using 4 Sinopoly 60AH (B) cells as my accessory battery. It is brand new but...

I had an issue with a parasitic load when I first installed the battery and it went completely flat. all cells were below 1v, one wouldnt register a voltage on my meter. I managed to get all of them back to life and holding a charge so I dont think that its an issue

Sag is about 110V at 600A. from 150ish (not bad with LA!)

I tried running without the acc battery. The only thing the dcdc was powering was the soliton and it cut out with a 12v too low error every time I stamped on the pedal.

Im starting to think the issue is just the fact that its not a very good piece of kit.

It definately shouldnt be getting too hot to touch!


Cheers

Mike

Unfortunately I can't offer you any advice with regards to how to fix your current DC/DC but I thought it might be appropriate to point out that Evnetics is currently working on a DC/DC converter that is designed for DIY Electric Vehicles. Just in case you were thinking of replacing yours (which it looks like you might have to).

[PStechPaul]

I'm not very familiar with the DC-DC converters used in EVs in this application, but as I understand it, it uses the full battery pack voltage (in this case 144V nominal, 110-150V swing), and provides 12 VDC (or 13.8 VDC for charging), at 400 watts, or about 33 amps.

Definitely the unit should not be getting so hot. At 90% efficiency it should only use 40 watts. But that was listed as maximum efficiency, so that is not a very useful specification:
http://www.chennic.com/show-products.asp?id=33&JCDI41

The wording is obviously written by someone who is not really fluent in English, so I also wonder about the technical qualifications of the designer and the quality of the components.

If you can get by with just 300 watts, and a 12V output rather than 13.8 for charging, you could use the following, which is just $97:
http://www.mpja.com/12V-25A-Hengfu-P...info/16488+PS/

It may not be well-known, but AC-DC switching supplies first rectify the line voltage, so for this supply, rated at 85-132 VAC, it will work on your battery pack from 120 VDC to 186 VDC. I don't know what the Chennic costs, but I think it may be a lot more. Of course this supply is open frame, so you'd need to enclose it and seal the connections for automotive use, and maybe supply fan cooling.

I really think it's better to have a separate battery for accessories, and use the vehicle mechanical power for charging, maybe with an alternator connected to the motor shaft. This would also eliminate the problem of the DC-DC converter being starved during acceleration. If it does not have an undervoltage lockout, many switching supplies will draw more and more current as the input voltage drops, until it can be enough to blow a fuse as you are seeing. But even at 100V input, a 400W supply should not draw any more than 5 amps. If you are melting 15 and 20 amp fuses in the primary circuit, there is definitely something seriously wrong. And the overheating is another telltale sign.

[EVfun]

Originally Posted by skooler

Hi all,

I thought a diode would be the answer, surely it would only need to be 30 amps though? .

What really annoys me is that is is advertised for use in EVs yet isn't actually fit for purpose! Grrrrr!

Anyway. U just popped another fuse in. The main pack is currently charging for the first time so I thought I'd get some juice into the accessory battery.

The dcdc has been running for about 45 mins and is too hot to touch. It is mounted on an aluminium sheet, the bonnet (hood) is open and it has plenty of air to circulate.

Its hot enough to make some insulation tape on a nearby cable feel takky.

Is this anything to worry about?

- must admit that I'm not impressed by it so far. Hopefully evnetics can build me a nice one for under $500 ;-)

The DC to DC really shouldn't get HOT while charging and with minimal 12 volt loads. When charging the ripple is limited to 120 Hz. That doesn't move a lot of amp hours in and out of the caps. I suppose it could warm the caps some.

The issue of the controller blowing the DC to DC fuse can happen because current can flow in and out of the caps 15,000 times a second as the controller draws power in pulses. This problem is somewhat new, and old, to the home conversion EVers. Controllers used to be largely unfiltered, just the capacitance needed to protect them self, back in the day of SCR controller running at around 1500 Hz. Then the Curtis PMC controllers came out and they have enough input capacitance that they didn't create a large 15kHz ripple. Later offering from DCPower Systems and Cafe Electric followed this trend. We got used to not having to deal with this high frequency ripple that can move a lot of amps back and forth (fuses measure the current both ways and add it up.) The Soliton and NetGain controller don't control this ripple on the DC bus. That means either the other items connected to the pack need to be built to deal with it, or the user needs to add that protection for them. It is actually easy if you follow the thread link I have earlier and listen to the posts from Tesseract.