Using Car Battery Chargers for your
EV Conversion

car battery charging

Email question: An electric car battery charger is really expensive. Car battery chargers, on the other hand, are cheap by comparison. So why can't I use a bunch of regular chargers instead, and save myself a lot of money? Do they really need a special kind of battery charger?

Answer: No, you're right, you CAN do that. A regular car battery is 12 volts, and if your electric car has 12 volt deep cycle batteries, the 12v battery charger will work just fine...

...on ONE battery at a time.

I do know people who do it this way, they've got 144 volt systems and have 12 regular car battery chargers hooked up separately to charge those babies back up. There are pros and cons to it, but it's better than a bad boy charger in a lot of ways.

How the "one battery, one charger" method works

The first person that I know of to successfully try this method is Dr. Larry Tillman in 2006. (Shall we call it the Tillman charger?)

He gave a lot of details of his system on this page of Jerry Halstead's EVConvert website, and several of the low-budget EV converters I've interviewed for Electric Cars are for Girls actually got their inspiration from Dr. Tillman's success.

Dr. Tillman's driven more than 10,000 miles on his EV using this method, so he's not just guessing it will work - it actually does work.

First, a little about Dr. Tillman's EV.

  • 72 volt system. (He's since upgraded to 84, but let's keep it simple.)
  • 12 volt 112 AH "deep cycle" marine batteries. (No, these are not usually recommended.)
  • 13 batteries total. 6 pairs of dance partners wired together in parallel, and an odd man out to run the accessories. Each battery having a dance partner increases the capacity of the pack (AH) and decreases the current draw on each battery (which is probably why he's doing okay with marine batteries).
  • Each pair is hooked up to the other pairs in series. I'm picturing a square dance with one big long rope linking all the couples together. The couples at each end of the rope have one hand on the rope, and the other hand on the motor.

  • And here's Dr. Tillman's charger arrangement:

  • Each pair of batteries has its own regular car battery charger. A 12-volt car battery charger like you can get at any auto parts store, or in his case, Walmart.
  • All the car battery chargers are mounted on a board. The board rides in the trunk sitting on top of the batteries.
  • Every car battery charger stays hooked up to its pair all the time. There's a blocking diode/rectifier bridge built into the charger which keeps the electricity from running from pack to charger, draining the batteries.
  • Each battery charger is plugged into a common power strip. Which he then plugs into the wall when he gets home.

  • Pros and Cons of the Tillman charger

    Reasons you might want to try Dr. Tillman's charging arrangement:

    • It's cheaper. Even if you get the cheapest manufactured EV battery charger, and the most expensive regular car battery chargers, the Tillman charger works out in your favor money-wise. Probably because companies that manufacture electric car chargers don't make that many of them, so there's no mass-production cost savings, but regular car battery chargers are mass-produced.
    • It's safer for your battery pack than a bad boy charger. Each of those individual battery chargers is doing the same babysitting job that a fancy EV charger does, and maybe even does a better job of it because each each charger is assigned to one battery, or in Tillman's case, one battery pair.
    • You get the parts locally. Dr. Tillman noted that he got his batteries AND his chargers at the local Walmart. This is handy if one of the chargers goes bad, you can just go down and get another one.
    • If ONE charger goes can just replace it with another one. It might take a whole hour (maybe two) before your EVs charging system is working again, good as new. On the other hand, if some tidbit of your fancy EV charger breaks, you'll be discussing it with the manufacturer, shipping things back and forth, and waiting.

    On the other hand, the cons, or just stuff to consider if you're going to do it this way:

    • The chargers are heavy. At 5 lbs. each (they're around that), 7 chargers weighs 35 pounds. That's more than your usual on-board EV battery charger.
    • Might trip your circuit breaker. Jerry made a couple of important points about the amount of juice being drawn from all those chargers plugged into one circuit. Dr. Tillman's chargers are all 2/4/6 amp chargers, you can choose which setting, and he usually chooses 6. But multiply that by 7 chargers all at once, and you can see why the circuit breaker might pop. Jerry recommends that you size your extension cords and power strip and wiring appropriately.

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