DIY Open Source EV Charger

[MPaulHolmes]

Nah, my calling is to be sworn at by middle schoolers. hahaha! But seriously, it sure is fun! I never knew electronics would be such a fun and creative process, and I get to use the programming experience! I love it!

[mcmahon.craig]

So, how do you make a steady 165v input source? All the charging algorithm stuff is just gravy with a micro-controller!

The old K&W 20-amp chargers couldn't charge above 108V packs because they couldn't increase the line voltage. You needed a "line booster" to do that (and even then they could only do 120Vdc).

So here's a crazy (as in fairly loony) idea. Instead of rectifying, feed your AC line voltage through a full-wave voltage doubler. That should give you about 340Vdc to run through your PWM smart bits and charge whatever you want. It would also allow you to charge from a dc source if you put in such an input behind the doubler. I'd also definitely want an isolation transformer on the input of such a machine because those'd be 3 fairly massive electrolytic caps you'd have in the input stage.

[Christopher Jordan]

Originally Posted by mcmahon.craig

The smart chargers I have used in the past usually cut off at 14.4V on a 12V battery.

Those Sears Diehards have reverse polarity, or dead cells, or some crazy relay. Started charging all 4 between 13.3V to 14.7V. 2 hours later 3 varied in the 13.5V range, but one dropped to 12.8.

Hauled the Diehard booster out and charged that low bat at 14.7 about 3 hours. Charge charge charge re charge. Pretty annoying.

I am getting to the point of buying 5 Diehard chargers, put them in 1 box (like an octopus with wires instead of legs; and charging all 4 (48V to 56V) at once, instead of spending a whole day charging.

[MPaulHolmes]

That's what I do too! I have 6 12v 6amp chargers ($20 each). It keeps them balanced, but it's pretty slow. When each one is done, it's charger shuts itself off on it's own time.

I'm going to read up on transformers and voltage doublers and who knows what!? I think it's a great idea to start with a really high voltage so the charger could work for anything from an AC system to a DC system. You could have a little knob on the side that would select what voltage you want to charge at. You could have another knob that would select if it's Lead Acid, NiMH, or Lithium Ion. Each algorithm is well defined. It's just a matter of controlling voltage and current based on some sort of feedback from the batteries. Wouldn't that be cool!? It might be good for there to be 2 knobs for voltage, so there could be 10, 20, ..., 320 (or whatever), and the other 0.0 through 9.9. Lithium Ion are weird. Each cell is 3.7v. The Lithium Ion batteries have almost the same charging algorithm as Lead Acid, as far as I know. NiMH is totally different. None of them are very hard with a micro-controller though, and a little high school math! I love how you can use math in the real world! It actually makes real stuff work. It's weird!

[roflwaffle]

Originally Posted by MPaulHolmes

I love how you can use math in the real world! It actually makes real stuff work. It's weird!

Welcome to the World of Tomorrow!



Great work btw!

[mcmahon.craig]

Originally Posted by Christopher Jordan

Those Sears Diehards have reverse polarity, or dead cells, or some crazy relay. Started charging all 4 between 13.3V to 14.7V. 2 hours later 3 varied in the 13.5V range, but one dropped to 12.8.

My personal experience is with Soneil chargers. They nominally charge constant-current to 14.4V and then float to 13.8V.

I am getting to the point of buying 5 Diehard chargers, put them in 1 box (like an octopus with wires instead of legs; and charging all 4 (48V to 56V) at once, instead of spending a whole day charging.

If you do that make SURE that the chargers are isolated. Check for continuity between the output and input leads, and if there is, it isn't isolated. Non-isolated chargers CANNOT be used in series or else you get blown fuses and general ugliness.

[MazdaMatt]

I did some reading on chargers and found the wikipedia page that explained that a "simple" charger either uses constant current or constant voltage, but may not be the most efficient... would it be reasonable to string 9 batteries in series and simply apply a wave-rectified, capacitor-smoothed wall outlet voltage across them? Sounds absolutely insane to me. I'm just thinking, if I had a 12 battery pack and had a dpdt switch that could make them either 2 parallel strings of 6 or one series string of 12 (not a difficult switch to imagine), then i could use a very gentle step-down transformer and a couple big capacitors to charge them...

again... sounds crazy to me, but that's what i gathered from a "simple charger" description.

[Christopher Jordan]

Originally Posted by mcmahon.craig

My personal experience is with Soneil chargers. They nominally charge constant-current to 14.4V and then float to 13.8V.

The Sears Diehard charger goes to about 16V then slowly drops to 14.7V for 2 hours, then shuts off. After charging floats to 13.2 - tops! Yesterday 1t stayed at 15V with those confusing computer chargers on-board. Unusual!

Each battery post has about 6 bolt-ons, clips, loose wires, fuses.... Take me an hour to undo everything for a simple daily charge. Multiplied the problem!

[MPaulHolmes]

Originally Posted by MazdaMatt

I did some reading on chargers and found the wikipedia page that explained that a "simple" charger either uses constant current or constant voltage, but may not be the most efficient... would it be reasonable to string 9 batteries in series and simply apply a wave-rectified, capacitor-smoothed wall outlet voltage across them? Sounds absolutely insane to me. I'm just thinking, if I had a 12 battery pack and had a dpdt switch that could make them either 2 parallel strings of 6 or one series string of 12 (not a difficult switch to imagine), then i could use a very gentle step-down transformer and a couple big capacitors to charge them...

again... sounds crazy to me, but that's what i gathered from a "simple charger" description.

I think that would be fine. You could have it shut off a tiny bit early when all the weirdness starts (the bulk charging is done, and hydrogen gassing might begin in earnest). Lead Acid is very forgiving during the bulk charging phase, or so I hear. I don't know what I'm talking about!

Actually, I think that's a really good idea. Charge 2 72v strings if you have a 144v pack. Then you could do without a transformer in the charger, and you could smart charge it with a micro-controller and PWM setup, just turned down a bit, since the rectified DC voltage would be around 160 or 165 (just a little bit less than the peak of about 170v.), and you could just run the pwm at 50% to get an average voltage in the 72v charging range.

I checked yesterday, and with 11 of my 200v ripple current capacitors, at 24v through the motor, there was a ripple voltage of 0.1v. I bet it wouldn't be that much ripple from the wall. I have no idea though. I need to test some of that crap out. haha!

[bennelson]

I just stumbled across a fairly inexpensive 72V charger!

Schumacher Multi Battery Charger — 10 Amp, 72 Volt, Model# SE-1072 | Battery Chargers | Northern Tool + Equipment



This charger is manually selectable up to 72V.

Thanks to Norm's YouTube video for the lead on this one.

This charger is about $220. It's not the exact same one as in the video, but manufacturers change the look of these products all the time.

http://www.youtube.com/watch?v=TONtT...eature=channel