[emosun]

The guy that built the car said all the (contactors/contractors?) weren't made for 72v and that the wires would all have to be replaced too , so I suppose I'll leave it at 36.

Also the motor appears to only be 24v so I'm already pushing it as is.

Here is my home made wiring diagram for charging two 36v strings with a 72v charger. The only way I can ensure the system won't short circuit is to use a knife switch so the wires cannot possibly get crossed when going from driving to charging mode.

The reason I have to use a 72v charger is because it's a 400$ charger that he simply GAVE me.

[emosun]

Course this could be avoided if only 3 boat batteries could get me 15 miles. then it would only be 150$ and I'd have plenty left over to buy a 36v charger.

Do you think only 3 batteries could get me 15 miles?

[Woodsmith]

I have a 24v motor on my tractor that is happily running on 48v with a view to going 72v in the future.

It could be an idea, if you want to stay with 36v, is to sell the 72v charger to raise the funds for the 36v charger and batteries.

[PStechPaul]

Well, I have heard that an EV typically uses 330 W-Hr/mile, but really good ones (or those driven very carefully under ideal conditions such as smooth flat roads and little wind), might do as well as 160. So let's say you can get 200. The deep cycle batteries I was looking at, at Tractor Supply, are 105 A-Hr each, for $85 each. So that is 12*3*105=3780 W-Hr. If you took them down to 60% of charge, you could go 3780*0.6/200=11.34 miles. If you are really lucky and don't mind banging the batteries really hard, you might just barely get 15 miles. But the batteries would soon weaken and then you'd be back to 10 and finally 5 or so.

It might be worthwhile to get a second opinion on converting the controller to 72 volts. I think it has a maximum speed setting which would probably limit the motor to 36 volts. I really doubt that the contactors would care about 72 or 36 volts. The controller has a chopper that drives the coils with 24 volts, and the contacts should be able to handle it. The wires will handle the same current, just a higher voltage.

Is there a fork lift shop near you? If you take really good photos of the controller using the manual as a guide, looking for such things as controls, part numbers, voltage ratings, and such for everything, maybe one of us can help you adjust it, or the forklift pros might be willing to do it for a nice lunch and a case of beer.

[PStechPaul]

Originally Posted by emosun

The guy that built the car said all the (contactors/contractors?) weren't made for 72v and that the wires would all have to be replaced too , so I suppose I'll leave it at 36.

Also the motor appears to only be 24v so I'm already pushing it as is.

Here is my home made wiring diagram for charging two 36v strings with a 72v charger. The only way I can ensure the system won't short circuit is to use a knife switch so the wires cannot possibly get crossed when going from driving to charging mode.

The reason I have to use a 72v charger is because it's a 400$ charger that he simply GAVE me.

Your diagram confused me because of the reversal of the red/black for +/-.

Actually you can get by with a DPDT switch if the car controller is disconnected while charging, or if the charger is only connected when charging and removed before running the car. You could also use a DPDT power relay. Here's a 30A one for $25:
http://www.surplussales.com/Relays/REcontacts-1.html

Wired properly, the paralleling contacts would only see 30 amps when you're pulling 60 amps on the motor. And such contacts will typically handle 3x their rating for short bursts. You're probably not going to pull over 100-150 amps for very long.

You can also add a power diode crosswise on the string for charging, if both sides of the pack are disconnected from the car while charging. Then you can use a DPST switch or contactor for parallel. But if you already have the knife switch, that's probably safest.

[Ziggythewiz]

Originally Posted by emosun

Course it would be even less complex if I left the system it was made for in place rather then trying to mess with it. I get the feeling I already mentioned I like the performance as is.

Except that it wasn't made for it. It wasn't made for anything, apparently. As I understand, you have a motor, controller, and charger that are made for 72V. You have contactors and 3 dead batteries that are made for 36V. Sounds like you're closer to 72 than 36. If you like it at 36, you'll love it at 72.

You will not get 15 miles on 3 marine batteries. You will be lucky if you can get that on 6. My car could not not get 15 miles after 8 months using 10 marine batteries.

PStechPaul left peukert out of the equation calculating the range you can get. Take what he said and multiply by .6

Expect around a 5 mile range for 3 batteries and a 10 mile range for 6.

About your contactors, how many are there? You don't need more than 2 and can get by with just one. $50 and you're running at 72V instead of 36. If I could double my car's performance for $50 I would have spent that in a second.

Whatever wires you're running will probably work better at 72 than 36.

As for switches, you will be pulling lots of amps continuous because of running at a lower voltage.

[emosun]

Originally Posted by PStechPaul

Your diagram confused me because of the reversal of the red/black for +/-.

Actually you can get by with a DPDT switch if the car controller is disconnected while charging, or if the charger is only connected when charging and removed before running the car. You could also use a DPDT power relay. Here's a 30A one for $25:
http://www.surplussales.com/Relays/REcontacts-1.html

Wired properly, the paralleling contacts would only see 30 amps when you're pulling 60 amps on the motor. And such contacts will typically handle 3x their rating for short bursts. You're probably not going to pull over 100-150 amps for very long.

You can also add a power diode crosswise on the string for charging, if both sides of the pack are disconnected from the car while charging. Then you can use a DPST switch or contactor for parallel. But if you already have the knife switch, that's probably safest.

I suppose I like the knife switch because it's really simplified and doesn't require any electricity to function. It also disconnects from the car while charging , and disconnect from the charger when driving with only a single lever. Thing is , the best switch I could find is rated at 100 amps , I have no idea what kind of amperage 3 boat batteries have tho.

[emosun]

Originally Posted by Ziggythewiz

Except that it wasn't made for it. It wasn't made for anything, apparently. As I understand, you have a motor, controller, and charger that are made for 72V. You have contactors and 3 dead batteries that are made for 36V. Sounds like you're closer to 72 than 36. If you like it at 36, you'll love it at 72.

You will not get 15 miles on 3 marine batteries. You will be lucky if you can get that on 6. My car could not not get 15 miles after 8 months using 10 marine batteries.

PStechPaul left peukert out of the equation calculating the range you can get. Take what he said and multiply by .6

Expect around a 5 mile range for 3 batteries and a 10 mile range for 6.

About your contactors, how many are there? You don't need more than 2 and can get by with just one. $50 and you're running at 72V instead of 36. If I could double my car's performance for $50 I would have spent that in a second.

Whatever wires you're running will probably work better at 72 than 36.

As for switches, you will be pulling lots of amps continuous because of running at a lower voltage.

I think he also mentioned that at 72 the batteries simply depleted twice as fast and the performance gain wasn't really worth it. I think 36 should do me fine.

[PStechPaul]

Yes, Peukert's number. OK, I found one calculator that actually works:
http://www.ajdesigner.com/phpbattery...umber_time.php

I don't know how much current you will draw, on average, but I think I assumed it would be 50A, or 1/2C. This is only about 2.5 HP, and that's really low for a road vehicle, but if you can get by using 5HP only half the time because you can coast down hills, maybe this will work. So the calculator gives a discharge life of 1.42 hours with Peukert=1.1, and just under an hour at 1.2. So, it depends if you can average 15 MPH at a 50 amp average draw.

Another way to look at it is using 330 W-Hr/mile, if your actual battery capacity is 50 A-H as the 1.2 Peukert says, you would have 3*12*50=1800 W-Hr and 5.4 miles. And that's running the batteries flat. The other thing to consider is the efficiency of the controller and motor, although that may be figured into the 330 figure. And as the batteries sag and become more depleted the motor will draw more current to maintain the same power, or at constant current/torque your speed will decrease.

Maybe if you replace the donuts with bicycle wheels?...

[emosun]

What would you say spec wise would be an ideal battery for this car. not battery setup , I like 36v. Just the battery to be used. If 50$ batteries wont last me even a year. Then how long does a 150-200$ battery last? I would hope it's 3 to 4 time more.

Today I compared the sheer size of the old golf cart batteries to the size of the boat batteries I was going to buy and THAT is what convinced me not to do it. I was going to buy them today , but they just look so small.

I've decide I'll attempt to save up for better batteries. Till then I'm just going to work on the car itself which is rusty and dirty. I replaced the hood and passenger door as a start.