Warning - DC-DC converters

[heathyoung]

Just a quick heads-up for anyone using the Lyen (or lyen style) unisolated DCC converters at close to their maximum input voltage - one day they will fail, and dump your pack voltage across whatever you are powering (oops!)

I was running 14S konions @ 57.6V fully charged for 2 years and randomly, out of the blue - the converter shorted its input to output and ran the magicshine headlamp at full pack voltage. Needless to say, it doesn't work now.

To avoid this happening - I highly recommend putting a zener diode across the output (eg. for a magicshine that takes 8v, a 12V zener would suffice), and a fuse on the input.

The simple switcher device (LM2596HV) was rated at a maximum of 60V, and I was running 58 - it worked for 2 years, but then without warning, exploded. Not due to regen or anything like that, just plugging the battery in, 10 seconds later - bang!

The type of converter I am talking about:

 

[neptronix]

...interesting.
I had a lyen "63v" unit fail at 62v within seconds, and i started getting 0v as the output.
After blowing more than one of these converters near the edge of their spec, i decided against using them.

Now for my magicshine, i use a 2S 5AH RC Lipo pack that i made from a 5S Turnigy pack that had a bad cell in it.

 

[nechaus]

yeah, id rather use a separate battery for other applications.. for many reasons but the main being that it can fail and blow stuff up

 

[miuan]

Why run converters with limited input voltage when most swithched wall plug supplies can do the same safely, at just about any battery voltage.

 

[gensem]

Im running a 120w 100v to 12v dc-dc converter with nothing but joy.
but its only running a magic shine and a horn so it will hardly overheat.

 

[Ykick]

Thanks for the warning as I've been toying with trying a DC-DC converter instead of a 3S Lipo for my Stella 200L and the occasional heated vest. Can you imagine one of these shorting pack voltage to my vest? That could possibly leave a mark...

 

[Tench]

Thanks for the warning as I've been toying with trying a DC-DC converter instead of a 3S Lipo for my Stella 200L and the occasional heated vest. Can you imagine one of these shorting pack voltage to my vest? That could possibly leave a mark...

You could end up looking like your Sig!! (if you dont allready)

 

[docnjoj]

I fried one of those DC/DC converters at 54 volts nominal or probably 60+ fully charged and Ed sent me a new one. I have 3 of them running at 36 volts now and they are completely reliable. I use one for the Magicshine at about 13 volts and another for my rear view camera and screen at about 14 volts. The third is on my wife's bike for her Magicshine. No problems in well over a year of running. Still a great converter and really easy to use.
otherDoc

 

[liveforphysics]

A zener is the wrong component to try to protect against it passing high.

You want a TVS. A big one. Or, a fuse in series with the output, and a smallish TVS.

 

[cwah]

I fried one of those DC/DC converters at 54 volts nominal or probably 60+ fully charged and Ed sent me a new one. I have 3 of them running at 36 volts now and they are completely reliable. I use one for the Magicshine at about 13 volts and another for my rear view camera and screen at about 14 volts. The third is on my wife's bike for her Magicshine. No problems in well over a year of running. Still a great converter and really easy to use.
otherDoc

That's great to see that the Magicshine works on 13V because it's rated for 8.4V.

Do you think the new magicshine MJ-880 would work at 12V? (I have a 12V DC-DC converter):

http://www.ebay.co.uk/itm/Magicshine-MJ-880-Bike-Light-Torch-LIGHT-UNIT-2000-LUMENS-upgrade-mj-872-/280819072247?pt=UK_SportsLeisure_Camping_LightsLanternsTorches&hash=item41621efcf7#ht_1195wt_1399

 

[docnjoj]

I fried one of those DC/DC converters at 54 volts nominal or probably 60+ fully charged and Ed sent me a new one. I have 3 of them running at 36 volts now and they are completely reliable. I use one for the Magicshine at about 13 volts and another for my rear view camera and screen at about 14 volts. The third is on my wife's bike for her Magicshine. No problems in well over a year of running. Still a great converter and really easy to use.
otherDoc

That's great to see that the Magicshine works on 13V because it's rated for 8.4V.

Do you think the new magicshine MJ-880 would work at 12V? (I have a 12V DC-DC converter):

http://www.ebay.co.uk/itm/Magicshine-MJ-880-Bike-Light-Torch-LIGHT-UNIT-2000-LUMENS-upgrade-mj-872-/280819072247?pt=UK_SportsLeisure_Camping_LightsLanternsTorches&hash=item41621efcf7#ht_1195wt_1399

Doc Bass in an old post said that the Magicshines are good up to 18V. I just use 12V and is is really bright.
otherDoc

 

[Farfle]

Why run converters with limited input voltage when most swithched wall plug supplies can do the same safely, at just about any battery voltage.

Agreed, medical power supplies are a good choice for this. They are rugged, isolated and and some of them have multiple outputs. Plus they come up as surplus pretty often. Most work down to 40-60v

 

[cwah]

I fried one of those DC/DC converters at 54 volts nominal or probably 60+ fully charged and Ed sent me a new one. I have 3 of them running at 36 volts now and they are completely reliable. I use one for the Magicshine at about 13 volts and another for my rear view camera and screen at about 14 volts. The third is on my wife's bike for her Magicshine. No problems in well over a year of running. Still a great converter and really easy to use.
otherDoc

That's great to see that the Magicshine works on 13V because it's rated for 8.4V.

Do you think the new magicshine MJ-880 would work at 12V? (I have a 12V DC-DC converter):

http://www.ebay.co.uk/itm/Magicshine-MJ-880-Bike-Light-Torch-LIGHT-UNIT-2000-LUMENS-upgrade-mj-872-/280819072247?pt=UK_SportsLeisure_Camping_LightsLanternsTorches&hash=item41621efcf7#ht_1195wt_1399

Doc Bass in an old post said that the Magicshines are good up to 18V. I just use 12V and is is really bright.
otherDoc

Thanks doc, going to get it then

 

[heathyoung]

Interesting - you guys in the US seem to have it easier finding supplies that will work on lower voltages, the only supply I could coax any output from was a nokia charger (5W woo.hoo).

Before you ask, yes, the supplies I tested were 100-240V ones, universal voltage input. Might buy one of those cheap chinese 12V DCC converters, they aren't that badly made (for the price, really).

I have another one of these DCC's that does something weird - it cuts out randomly after a few minutes and only goes back on when the battery voltage drops (like a HVC - odd).

 

[ZOMGVTEK]

I purchased the lowest cost 7.5V SMPS I could find on eBay, and it works fine on my 24S pack. It was SUPER cheap, is small, light, and 'works' down to 60V or so. The only issue is it won't start up loaded down at lower voltages, so I need to switch the load rather than the power to the SMPS. No biggie, it takes very little power without a load.

Something like this...
http://www.ebay.com/itm/AC-To-DC-7-5V-2A-Power-Adapter-Adaptor-Converter-/130622778120?pt=LH_DefaultDomain_0&hash=item1e69b96b08#ht_3955wt_1413
I popped open the cover on mine, and it sure was a low quality supply, but it does work, and vibration probably isn't an issue given how few components were on the thing.

Mine was cheaper, but I also purchased it quite a while ago. Doc claims some Magshines take 12V+, but IIRC he says one model won't. I just used a 7.5V adaptor and it works fine, mine shows green on the battery indicator.

 

[cwah]

Doc claims some Magshines take 12V+, but IIRC he says one model won't. I just used a 7.5V adaptor and it works fine, mine shows green on the battery indicator.

Do you know if the mj-880 works with 12V? I prefer not to use an adaptor

 

[ZOMGVTEK]

Doc claims some Magshines take 12V+, but IIRC he says one model won't. I just used a 7.5V adaptor and it works fine, mine shows green on the battery indicator.

Do you know if the mj-880 works with 12V? I prefer not to use an adaptor

My understanding, is that the '3 mode' SSC 900 Lumen model does not, and the 1000 Lumen model with the red/green/orange/red LED on the button does. However, it's entirely possible thats backwards. Doc said something about it somewhere, might be hard to find...

I recall reading what Doc said about them, and I have the 3 mode one, but I'm running 7.5V on mine. Could be due to the fact that Doc said it won't take more, I don't really remember. Regardless, 7.5V is well within its normal range, and should be quite safe if you're unsure.

How would you get 12V on your bike? Do you have a 12V system? The voltage of that is probably going to be >12.0V. If you already have a 12V power supply on the bike, thats perfectly fine. Roll the dice and hope for the best?

 

[cwah]

Thanks Zomtek. I'm going to see if there is any post related to the latest magicshine.

I know 7.5V will work. But my point is not to use a second DC-DC converter for my light. I'm trying to remain "light"

 

[TonyReynolds]

Looks like what may be needed in this application is a golf cart dc to dc converter:

http://stores.ebay.com/EVsupplier/_i.html?_fsub=1636847014

I'm currently looking to go from 52VDC to 12VDC, and it looks like there are many small, circuit-protected units available on eBay...

 

[ebent]

I use a dc converter from Thunderstruk http://www.thunderstruck-ev.com/green-galaxy-36-72v.html 2 years of constant use and no trouble.

 

[heathyoung]

Hmmm... That looks familiar, one of the converters I was thinking of getting.

http://www.ebay.com.au/itm/160733960418?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Not badly made, I repaired one for someone who reversed the polarity of the battery (only blew an on-board fuse, why couldn't the manufacturer have fitted a bloody diode).