[jonescg]

Hi All,

For those who don't know, I'm working on an electric race bike destined to compete with Ripperton's machine this June. All of the 12 V auxiliary stuff is to be powered from a 12 V battery, and this battery is to be recharged between races. It will work for now, but later on I was thinking of getting a DC/DC converter to keep the auxiliary battery topped up.

Here's the problem - the DC bus of my battery pack is 700 V when fully charged. I have isolating contactors which can break the pack up into four equal parts using a half pack contactor and two quarter-pack contactors.

So when I charge the pack, I use two 350 V max chargers and charge the bike as two half packs - no centre tap.

My question to the DIY EV crowd - what is your experience with running the likes of Vicor DC/DC converters with the inputs in series? I understand that a centre-tap is desired, but is it necessary?

If a 700 V capable DC/DC converter existed I would gladly use it. Anyone know how to build one?

Thanks in advance,
Chris

 

[dcb]

just curious, how many amps do you want to charge at? (how many amp hours used in a run and how long between runs?) Also what is your wall voltage and current availability (and frequency)?

 

[jonescg]

Oh, probably about 10 or 15 amps output. I have coolant pumps and fans, contactors, instruments, controller etc, so maybe about 10-12 amps load in total. Racing will be for about 10 minutes or so, but when I eventually make this thing a road going machine I want some level of convenience with respect to keeping the auxiliary battery charged up.

We run 230-250 V AC, 50 Hz in Australia.

 

[frodus]

I'd just hook a Vicor on each half pack. They are isolated, so hooking the outputs together won't matter. There will be a fairly small difference in current sharing between the two (unless you do one of the current share circuits they offer in the apps manual) and might not matter to you since you're charging each half pack separately anyway.

I did this with 2 48V dc-dc's on a 96V pack. Hooked the 12V outputs together. Center tapped.

Haven't tried with the center tap floating.... not sure how well that'd work.


You might even talk to Vicor about making a 700V dc-dc for you. They do all sorts of custom stuff.

 

[dcb]

I could possibly see an issue with hooking up two pwm devices in series (one trying to turn off while the other turns on fighting over control of the voltage/current) , the center tap should eliminate that. You shouldn't need a bunch of relays, as long as they are really isolated.

Is part of the issue that the max is non-isolated?