DIY Electric Car Forums banner

1 - 2 of 2 Posts

ยท
Registered
Joined
ยท
1 Posts
Discussion Starter #1
Hello! TLDR, SKIP TO BOTTOM PARAGRAPH ๐Ÿ˜ƒ๐Ÿ˜ƒ
Just got myself a pile of crap with good intentions in the local classifieds. The story goes that the old guy (87 years old) did the conversion using a golf cart. It does look like he just hacked off the parts of the 98 Pontiac Firefly that he didn't need and added the parts from the golf cart to make it work. A lot of "farm-gineering" in this one but she moves as is. It's home was a small island community and it probably was fine as is there.

There are lots of things wrong that are obvious but I'm looking for some tips to at least optimize what i have our learn from what is there and improve. The motor is Advanced DC Motors at 48v, rated AU2500 2-20-04 Class H. No idea what that means... That's all that i can really read from the motor. The controller is a plastic box that I'm certain is straight off the cart. The batteries are 6 x 8v 170ah wired together in series with all different gages of wire and not one of them strapped down and not one terminal protected from accidental short then covered with a scrap of carpet.

Performance is weak. Some of the wires heat up way too much. I need to use all the gears in order to get it up to speed. On the few trips I've taken her on I've gotten up to 60km/h easily on flat, the hills are another story. I'd say the top speed could be about 80 on the flats given enough room to get there but it's going to be too dangerously slow on the highway where the speed limit is 90. I have BCAA so on the maiden voyage home after purchase, I ran it till the batteries were low enough to make me quit and then got a tow home, so the range is about 20km. The real win is that this car has already been re registered as electric so I won't need an inspection as i would if i was starting my own conversion.

I've read some bad news about this type of setup but it has already been done. so instead of telling me that it won't work, does anyone have some ideas to optimize? Ideal range would be around 40km a mix of highway speed (90 km/hr) and city driving.

THE REAL QUESTION:
Battery bank upgrade and safety improvement is simple and within my knowledge and ability. What i don't know is if i can overvolt the motor and by how much. Will the controller handle that? What are the risks and what should i watch out for? Can i just add one 12v battery in series one at a time and see what happens? If for only small experimental trips does this negatively effect the current battery bank?

Thanks for any tips. I've been dreaming of doing this for years now. Stoked to start tinkering.
 

ยท
Registered
Joined
ยท
1,122 Posts
Let's just slam through your specs...

The motor is Advanced DC Motors at 48v, rated AU2500 2-20-04 Class H. No idea what that means. .. That's all that i can really read from the motor.
Picture with a ruler is worth a thousand words. Also, how much does it weigh?

- 48v is the design voltage.
- AU2500 might be a UL Certification for "people mover" motors.
- 2-20-04 is probably the date, Feb 20, 2004.
- Class H is the insulation type I think, doesn't really matter much.

https://www.ebay.com/itm/Advanced-DC-Motor-XP-1837-Volts-DC-48-Class-H-AU2500-New-Surplus-Old-Stock-/252636249047 <-- That one?

Probably rated for ~6 hp (4800 watts or so).

It's probably a series-wound DC motor.

That's roughly all correct for a golf cart motor.



The controller is a plastic box that I'm certain is straight off the cart.
Get a model number, or take some pics. Even just seeing how many terminals it has will help.

This will be your bottleneck quite likely.

The batteries are 6 x 8v 170ah wired together in series with all different gages of wire and not one of them strapped down and not one terminal protected from accidental short then covered with a scrap of carpet.
I like this old man already.

Watts = Volts x Amps
Watthours = Volts x Amphours

6 x 8v x 170ah = 8,160 watt-hours, assuming new, assuming you can get full energy out of them (you can't, you'll lose probably 40% because they're lead acid).

Performance is weak. Some of the wires heat up way too much. I need to use all the gears in order to get it up to speed.
To travel highway speed requires around 12 horsepower. It's nonlinear, so, it makes sense that with 6 horsepower you could slowly accelerate to 80km/h, that's about right. That's surprising actually.

The wires, umm, should all be equally thick since all batteries are in series. The thinner ones are obviously getting overloaded.

Needing to use all the gears makes sense. Normally you wouldn't need the gears, but your wires are so thin and your extra power is so minimal that you need to be as easy on the motor as possible.

I ran it till the batteries were low enough to make me quit and then got a tow home, so the range is about 20km.
Travelling at highway speed uses roughly 10,000 watts. You don't get there, you're travelling at 80km/h and using probably 6,000 watts. You have 8160 watt-hours and lead-acids are going to let you get at maybe 60% of it that quickly (100% is when discharged over 20 hours, you're trying to squeeze them dry in 20 minutes). Roughly 5000 watt-hours available then, brand new batteries.

Driving 80 km/h to 20 km means your drive lasted 1/4 of an hour or 15 minutes. Presuming 6,000 watts draw for 15 minutes, that's 1500 watt-hours. For old shitty batteries with crap wires and probably at least one of them failing... to have 5000 watt-hours new and only get 1500 watt-hours out of them, yeah, I can see that.

In series the chain is only as strong as its weakest link, so, a bad battery will kinda kill the pack.

I've read some bad news about this type of setup but it has already been done.
This type of conversion was what every EV conversion was doing in 2000-2010 or so. The motor is still a popular way to go, but no one uses lead-acids anymore, they're more expensive in to replace than the range their lifetime can get you compared to gas.

so instead of telling me that it won't work, does anyone have some ideas to optimize? Ideal range would be around 40km a mix of highway speed (90 km/hr) and city driving.
Let's say 100km/h because it's an even 10,000 watts or so, and that's some extra power to accelerate or not die on a hill. City driving will be half that or less.

Let's presume all highway, no starts and stops.

At 100 km/h, to go 40km that's 40% of an hour (24 minutes). At 10,000 watts, that's 4,000 watt-hours.

- A Tesla will have 70,000-90,000.
- A Nissan Leaf has 24,000 watt-hours of battery.
- An average cordless drill will have 100 watt hours.
- A laptop perhaps 50 watt hours.

That should give you a sense of scale for size, weight, and cost.

What i don't know is if i can overvolt the motor and by how much.
Motor, certainly yes. 80v easy. 120v probably fine by advancing the brushes. (Rotate the brushes 5-10 degrees). The consequence of not advancing the brushes is worse arcing and worse brush life.

Will the controller handle that? What are the risks and what should i watch out for? Can i just add one 12v battery in series one at a time and see what happens?
This will work perfectly until it blows up your controller without any prior signs of failure. So the question is: "Do you want to wreck your controller?" because it's guaranteed to. The failure method will be the insulation inside the power transistors (probably MOSFETS) failing and them burning up instantly, internally. It's not suited for trial and error.

So, find out what your controller is, find out what the MOSFETS in it are rated for, and then maybe guess at how much you can exceed the original pack voltage.

Thanks for any tips. I've been dreaming of doing this for years now. Stoked to start tinkering.
Suggestions:

1 - Replace, or supplement the wiring so it's at least equally thick. If the wires are getting hot, you're wasting energy and limiting power. Don't go spending a lot of money, you'll probably throw the batteries away later anyway.

2 - Open up the batteries and check their water levels. Add distilled water to any that are low. An 8v batter should have 4 cells each I think.

3 - Charge each battery individually with a power supply if you can. An 8v battery will charge to 9.6v I think. If it's sat for a long period of time, charge it to 10v for, I dunno, a day or so. They'll get hot but not too hot, this helps restore the plates a bit (while also, somewhat damaging them in other ways, don't do it often, but, once after sitting a long time is good). If you don't have much for a charger, rearrange them in parallel to do the charging so at least you don't have to sit there and switch wires 6 times.

4 - After the batteries are fixed again, maybe try discharging them again when wired in series (so they each have equal energy withdrawn). If convenient, drive in circles. If not, wire them to a kettle or something as a load. Use a voltmeter to watch how each battery loses voltage. If one of them drops to 8 volts long before the others do, it's a crappy battery, it might be the cheapest option to replace it.

... Those are all things you can do to refine your setup without changing it. Here are more you can do to change your setup...

5 - Find out the limits of your controller for both voltage and current. If it can handle it, you'll know what size of battery to find.

6 - You can't make your battery voltage any higher by rearranging them because they're already as high as they go. It's probably not cost effective, but it would be very effort-effective to just add more batteries, up to the max your controller (and I suppose your charger, though that's easier and cheaper to fix) can support. This will both add to your range and to your power. The motor is fine without changes up to, oh, 72 volts, might start to see more arcing 72-96v, and above 96v should really be modified by advancing the brushes. Rough ball parks.

7 - Throw away those bullshit leadacids and throw in some used Nissan Leaf cells. A few hundred bucks will completely swamp the capabilites of your old battery bank and be 1/3 the weight. If you keep the voltage the same, neither the motor or the controller will care, it's completely modular.

8 - Upgrade your controller.

9 - Upgrade or supplement your motor, which is underpowered by probably 35-50% for the size of the vehicle and a comfortable driving habit.

10 - Buy an OEM EV.

Keep asking questions, most people here are happy to help.
 
1 - 2 of 2 Posts
Top