Wallwart switched PSU's for 12V accessories in e-vehicles

[jag]

Instead of buying a purpose made DC-DC converter from EV battery voltage to 12V to run accessories various people have reported success with general purpose PSU's

Here are my experiences:
Silverstone 500W PC ATX PSU in my robot PC: Needs >100V to start (trigger some logic), but then will output respectable power (tested about 200-300W) down to about 40V.
Had similar results with 1U server grade PSU's we have at school.

Now these are a bit big to put on my ebike, and I cound;t figure out how to bypass the 100V circuit needed to start them.

Next I thought I'll try wall-wart PSU's of the type that comes with most electronics nowdays. Bought a couple of camera chargers (one aftermarket for Nikon $1.99 on sale, 6.5V 2.1A, one Canon 7V 2A $3.99). Thought was to either run a Vetta 6V 10W halogen bike light or double up the wallwarts and run a 12V light of my 48 and 72V bike batteries. First the positive was that these chargers start at both 48 and 72 V. The negative: Unloaded or lightly loaded they put out the rated voltage, but at loads over 1A voltage dropped to half. I must be too cheap! I guess I'll try a laptop PSU next.

 

[AussieJester]

Maybe try one of the pc 12 volt psu as per used in car pc setups, they are small
not alot larger than a smoke packet, dunno how they would handle 48v and above though
or what to do to make them handle it...for 25 bucks you can buy 48-72v to 12v converter so
its easier and nearly as cheap to get one thats made for the job than ghetto it..IMO

KiM

 

[jag]

Maybe try one of the pc 12 volt psu as per used in car pc setups, they are small
not alot larger than a smoke packet, dunno how they would handle 48v and above though
or what to do to make them handle it...for 25 bucks you can buy 48-72v to 12v converter so
its easier and nearly as cheap to get one thats made for the job than ghetto it..IMO

KiM

Thanks for the link. $25 for a 10A DC-DC is not bad. I might also look into if there is a Vicor that does 48-12V. Looks like members buy those for just a few $ a piece from surplus sources.

Now for my own (more unpractical) thoughts:
The problem with making a 110V PSU give the rated current at just 48V in is presumably that the winding ratio in the transformer is wrong, and varying the PWM modulation can only compensate so much (I was suprised how tolerant the Silverstone PC PSU was, but that is obvioulsy higher quality gear than a $1.99 wall wart). I briefly considered re-wiring the transformer, but that would mean hours of work. Another option is buying a 110 to 24V wall wart. This would have a more fortunate winding ratio. Then change the output regulator to 12V. Anyhow, didn't see dirt cheap 24V wall warts yet so shelved that thought for now. Having already invested $1.99+$3.99 I was wondering what I can do with the wall warts. One went to power baby's toys (saving batteries). The other one remains.

That lead to the following idea: The wall wart is exactly the shape and size of those Volt Phreaks chargers people use as single cell chargers. I remember posts some years ago about people cracking them, open and finding the regulator circutry/resistor. I couldn't fin the thread again though. Can someone point me in the right direction?

My thought was that the transformer ratio ought to be about right to drive a high power LED chip I have in school. Just have to change so the regulator does constant current (CC). End result is hopefully an inexpensive universal LED light ($5 LED chip + couple $ for wallwart and extra resistors/components for CC) that could easily fit into the casing of a regular bike light with the batteries and inefficient incandescent bulb gutted out.
What do you think? Any advice?

 

[amberwolf]

If you're going to be re-engineering stuff you might just want to look into Roman Black's converters. They're very efficient, and should be easy to scale up to higher voltage and current levels, if you already know enough electronics to alter existing SMPS designs.
http://www.romanblack.com/smps/smps.htm
http://www.romanblack.com/smps/a05.htm