switching power supply as DC/DC converter...issues???

I'm wrapping up my current build with a 31s pack (115v nominal). Due to the high voltage I figured the cheap and easy route for my 12V for lights was to use one of the 12V power supplies I have around the house. It seemed like my best candidate, since I expect about a 2A load at night, was the Wii power supply. It puts out 12V and 3.35A. I tested it first with a direct connection to the battery pos and neg, and it seemed to work.

Now after 2 days of wiring, fabbing brackets, fitting the Wii supply into my limited space, the darn thing is acting weird. ie sometimes it comes on when I turn on the key, and sometimes not, and that's just not going to work for me. The only thing different from the other 12V switchers I have is that it says input 110V AC, not the usual 100-240V AC.

Could this darn thing somehow be polarity needful on the input? I tested it both ways before installing (but not repeated on/off), so I didn't even pay attention to which input wire got the +115V from the keyswitch.

I don't have any other supplies that can do 12V at over 2A. Would it be okay to connect 2 or 3 paralleled at the input and output?

Assuming the keyswitch is connecting battery power to the "wallwart", first thing I'd do is bypass the switch providing the power, and then connect/disconnect the power wire manually and see if it turns on every time that way.

If it does, the switch is the problem (possibly arcing inside at the high voltage, possibly leaving stuff on the contacts preventing good connection, but htat gets wiped off enough to work sometimes).

If it doesn't, work that way any better than before, it could just be unable to reliably start on DC input vs AC. (I have an Xbox PSU that can't start on DC at all even if it's the same voltage as teh AC would be if it were DC)

It is possible, that polarity might matter if it isn't gettting AC, if some of it's circuitry only work on part of the AC cycle. I'm pretty sure that's why my xbox PSU won't work on DC--part of it works on one half the cycle, and the rest works on the other. So neither polarity DC lets it startup. It's just not a common problem.

It's also possible that the load at startup is too high for it, and it's shutting down on some startups because it's right at the edge. Try switching it on without any load on it, or at least with the headlight(s) turned off. Then turn the load on after the PSU is on, repeatedly, and it'll work fine if this is the problem. If the load is just plain too high it'll shutdown when the load is applied (but not when it isn't).


Paralleling may work, or it may not, depends on how the output stages are designed. Occasionally you find some that only startup if there's no voltage on the output; if tis' already detecting the "right" voltage it might not startup, so if some of the paralleled units don't startup as fast as others, the first one(s) might be all that power up correctly. Most likely paralleling will work ok, but I wouldn't guarantee it.


In general I find that more of the wide range (100vac-230vac / etc) wallwarts work on DC than any other, and work at lower startup voltages (down to around 50VDC often enough, but sometims only 60-70VDC).

Side note: if you can find 14-15VDC output wallwarts (like some NICD/NIMH/SLA-powered device chargers use as a base PSU, not the charger itself), with taht wide-range input, they'll work better to run automotive-type lights and accessories than 12VDC output stuff.


That said, if you don't want to deal with any of that, I have a couple of used Sevcon DC-DC units with automotive level outputs that were for 28s Li-ion type packs, so they won't work with mine. I'll have to check what their input range is, but I'd part with one cheap+shipping (just want to be able to get one that *does* run on my 14s setups).

While testing "AC" USB power blocks for my bike, I ran into many that would only work on a certain polarity on my 52V pack, didn't really spend much time thinking about why but it was definitely a thing.

Thanks AW. I got it working fine now. I had the neg battery wires of my controllers disconnected from the battery, and somehow there was voltage leaking back through the system, 0.3 milliamps, which was confusing the power supply. Once I connected the controllers' negative to the pack the bleed down resistors ate any leakage, so it now comes on when I turn the key on under all conditions. This will be my first time with full lights. I've been running brake lights for a few years, and now I'll have blinkers too. I had to go with incandescent turn signals on the rear and LEDs up front, since the little motorcycle blinker relay I picked up wouldn't respond to LEDs only.

The only thing left to prove out is to verify that it still works at top of charge. It definitely works at lowest voltage, since I tried it at 80v, so I don't expect issues at my 129V top of charge. I've got my fingers crossed to finally test ride tomorrow. I've grown tired of motos catching whizzing by my 16kw MidMonster powered rocket scooter after slaughtering them leaving red lights, so with 29kw fed into the higher Kv HubMonster I'll get passed only when I allow it.

John in CR said:

I had to go with incandescent turn signals on the rear and LEDs up front, since the little motorcycle blinker relay I picked up wouldn't respond to LEDs only.

Click to expand...

You can add power resistors in parallel with the LEDs to fix that. Autoparts places around here often sell those "ballast resistors" along with LED replacements bulbs, so older cars' blinkers still work with them.

BUT: It's much easier to just get a new little blinker that does work with LED or incandescent equally well; that's the kind I use on my bike and trike:

It's a 3-wire type, so it connects to 12v+ and ground, with a signal out that goes to your blinker switch common wire.
https://www.google.com/search?q=Novita+EP35&ie=utf-8&oe=utf-8

Thanks for the info AW, but I'll stick with my $2 moto blinker relay and the super cheap incandescent turn signals as my power resistors. You know me, extreme power at the lowest cost. It's good to know about those LED blinker ballasts, but with shipping and duties I'd be looking at the $8 I wouldn't pay to begin with turning into a $20 in my hand cost down here.

I'll do a deal on those Sevcon DC/DC converters that are too high a voltage for you, since I have some 28s builds coming up. What's on your wish list that I can send your way?