The converting, maintenance, and operation of a Suzuki Samurai conversion to Electric power.

Tuesday, May 8, 2007

On board charger

I've been carrying a simple "bad boy" charger for opportunity charging. A "bad boy" is a 1 inch square by 1/4 inch thick bridge rectifier attached to a cord. It takes the ac and converts it to dc. This produces around 150v dc which is enough to add to the charge of a low 144v pack, but not enough to fully charge it. The design goal was to have a plug it in and forget it charger so my wife could use the car in my absence. The WWII charger I am using requires more adjustment than she would be comfortable with.

Rich Rudman of Manzanita Micro sells a nice charger, but it is $2000. I actually considered it. Then I remembered that I wanted to experiment with a boosted "bad boy." I had purchased a 12V 20 amp transformer on EBay for this purpose some time ago. Time to get a round tuit.

I used Tom Martins schematic at and it worked exactly as advertised. The concept is to put the transformer in series with the 110v electric line so the 12v is added to the 110. The addition of a dimmer allows the addition of less than 12v. (The numbers refer to the mean voltage on AC. The DC from the rectifier will be about 40% higher.) When the pack is low, about 16 amps will be fed to it. Might have to use the dimmer to avoid tripping the breaker of the outlet plugged into. I measured 3 amps flowing into a fully charged pack at 179v, so overcharging shouldn't be an issue. ANY UNREGULATED CHARGER MUST HAVE A TIMER. I found 15 amp GE timers at Ocean State Job Lots for $3! Without a timer, forgetting about the charger can be a very expensive error.

It is also recommended that ground fault protection be included in the circuit to protect against possible shocks. The least expensive GFI is sold in the form of a duplex outlet. For some reason, if you buy it in the form of a circuit breaker, it is much more expensive.

So, we have a GFI outlet, a 600 watt dimmer, a timer, a transformer, and the rectifier to be mounted. Have to think about where. Also have to consider how the vehicle will be plugged in. The cutsey approach is to use the gas filler for the power cord location. One problem is the possibility of driving off without unplugging the car. The current scheme requires the hood be open while charging which solves the driving off problem, but I wanted the new system to be simple.

I wanted to make use of the existing volt and amp displays to monitor the charge so it made sense to mount the charger controls in the passenger compartment. If the plug was also inside, the drive off problem would be unlikely to occur. I searched for a metal triple size electrical box, but couldn't find on, so went with 3 singles. The outlet with plug in pigtail, the dimmer, and the timer are each in a box on the dash. The boxes are side by side with modified plastic conduit connectors connecting them. I made a cover plate of clear plexiglas. The back of the plexi was painted with black spray paint. Really looks nice! The transformer was mounted under the hood and the rectifier is below it, bolted to the 2" aluminum angle used for the battery mount. This should make a great heat sink to keep the rectifier cool. Hook up the wires and it works!

I am told that the charger can be made more efficient by adding an inductor and capacitors to smooth the current. Perhaps more will be done when I get more information. For now, set the timer to charge for 1 hour for each 3 miles driven and plug it in. If it is charging at more than 15 amps, turn down the dimmer a bit.

1 comment:

Anonymous said...


Looks like a great idea for a charger! We'll have to talk about this at the next NEEAA meeting.

I'm probably going to go the purchased charger way with a Russco. I'm looking for a plug-in and forget solution to charging.

See you next meeting!