# Help converting a Cushman 36v cart to hybrid vehicle? (charge while driving)



## major (Apr 4, 2008)

Singinius said:


> Hello,
> 
> 
> I have a heavily modified Cushman 36v cart and I am wondering if someone can help me understand what I need to do to be able to charge the batteries while I am driving it?
> ...


Hi Singi,

Why do you want to do this?

Basically you can't charge and use a battery at the same time. Using a battery is discharging it, which is the opposite of charging it. So what will happen when you put a charger on the battery while it is being used is that there will result a net charge rate or current which either charges or discharges the battery. Call it positive current which charges and negative current which discharges the battery. If the load (motor propelling the vehicle) current is more than the charger output current, the net current is negative and the battery discharges. If the charger current is more than the load, the battery charges with the positive net current.

So your charger current is 20 Amps. At 36 volts, that is 720 Watts (20A * 36V). 720W is less than one horsepower (1hp = 746W). So the maximum power the motor could use to propel the vehicle and have a net positive current to actually charge the battery would be less than one hp, probably close to 1/2 hp. 

So with the equipment you describe, to charge the battery while driving, you need to go so slow as to use less than 1/2 hp. It probably is not possible for you to even move that vehicle with that little power.

And another thing, the battery charger may not work properly when the traction circuit is on. It depends on the particular charger.

You would be better off using all electric or all gas engine for propulsion. 

Regards,

major


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## Singinius (Sep 14, 2011)

Major,

Thank you for the reply. This is for an art car that is driven at Burning Man. Essentially the vehicle is only used at this event so we have a finite amount of time to use it every year. We upgraded the batteries last year and using the stock charger (which might be a couple amps larger than the Schauer) we got pretty good amount of usage from the vehicle during the event. However we would like to increase the amount of time the vehicle is available and decrease the amount of time we need to have it charging. 

obviously, one approach would be to be able to charge it while we are using it, but I understand your point about total power output of the charging system.

If we don't charge it while we are driving it then I suppose just using a charger with a larger current capacity would get us the improvements we are looking for? 

Are there 30-40amp 36v chargers available? 

Thanks,
Sin


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## onegreenev (May 18, 2012)

Nothing wrong with taking the gen and charger along for the ride and when your stopped for an event you can let the little cart charge up then go for another ride then charge again. Opportunity charging during events. That would work and you would not have to beat feet back to the normal charging station each time. It really is the only practical way to do that.


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## major (Apr 4, 2008)

Singinius said:


> Major,
> Are there 30-40amp 36v chargers available?


Probably, but they would likely require 240 VAC. If the generator output is 3000VA and 120 volts AC, then you might be able to run three high current 12 volt battery chargers and get a quicker charge. Maybe look for 40 or 50 amp 12 Volt battery chargers. Make sure they are isolated (most are).


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## thingstodo (Jul 16, 2010)

major said:


> Why do you want to do this?


 I think that Sin would like the vehicle to move for as much of Burning Man as possible without the inconvenience of stopping near a charging outlet.

In other words, a range extender.



major said:


> So with the equipment you describe, to charge the battery while driving, you need to go so slow as to use less than 1/2 hp. It probably is not possible for you to even move that vehicle with that little power.


Please clarify, Sin. Did you mean that you want to charge while driving (have the batteries store more energy) or that you would like to keep the generator and battery charger supplying power while driving as well as while the Cushman is stopped so the batteries have power to move when you would like the Cushman to move (battery charger supplies some of the energy to the Cushman so the battery discharges less and the Cushman will move for longer)?



major said:


> And another thing, the battery charger may not work properly when the traction circuit is on. It depends on the particular charger.


That is a good point and it would have to be tested. I looked up the link for the charger and it seems like a typical two-stage charger, but there is no info on the electronics used.

In my humble opinion it will work OK for Sin to try this out. I see no obvious way for the battery charger or batteries to be damaged by performing this simple test .. but that is only my opinion. I would have no issue doing the test if it was my equipment.


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## DIYguy (Sep 18, 2008)

I've used a charger while driving for range extension. Of course you can only call it "charging" if there is a net positive amount of energy as Major describes. That said, it can still increase your run time. 

My personal opinion though, is that it is really loud, and messy and goes against what most people want to achieve with electric drive. 

Perhaps opting to spend funds on lithium cells as opposed to AGM's and a generator would get you the run time you need?? How long is this event? You should be able to get enough lithium in a golf cart to drive it steady for half the day I would think. . . without doing any math here.....


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## Singinius (Sep 14, 2011)

> Please clarify, Sin. Did you mean that you want to charge while driving (have the batteries store more energy) or that you would like to keep the generator and battery charger supplying power while driving as well as while the Cushman is stopped so the batteries have power to move when you would like the Cushman to move (battery charger supplies some of the energy to the Cushman so the battery discharges less and the Cushman will move for longer)?


I would like to be able to leave the generator running at all times (moving or stopped) if possible. The vehicle is used for a 7-10 day period in the middle of the desert. It is not a practical EV build it is essentially an expensive toy. 

When the vehicle is used at night the generator is always onboard and running anyways. We are not using nearly all of it's available power just with the lighting system. 

With all of the heavy frame modifications and hauling 6 or 7 people we are straining the system as it is. Anything that flattens out the rate of discharge on the batteries is worth considering. We could easily be going 10 miles a day with driving around the site and ferrying people and supplies about. 

I figure a photo may help clarify:
http://www.flickr.com/photos/singinius/7626132024/

Sin


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## Mike Leach (Feb 3, 2012)

Hey, nice ride captain.lol Has anyone ever tried using a generator rated at the voltage equal to the battery voltage. This vehicle is a 36 volt, could you use a 36 volt generator or would there be an A/C to D/C problem?

I am just about finished my first conversion at 48 volts and was thinking about a 48 volt generator on board.


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## thingstodo (Jul 16, 2010)

Singinius said:


> I would like to be able to leave the generator running at all times (moving or stopped) if possible. The vehicle is used for a 7-10 day period in the middle of the desert.


It would be a good idea to test that the charger extends the run time of the Cushman before you count on it at Burning Man. I think it should work well for you.



Singinius said:


> When the vehicle is used at night the generator is always onboard and running anyways. We are not using nearly all of it's available power just with the lighting system.


Assuming that your test shows everything working as expected, if the charger is too much load for the generator in the evening when you are running a bunch of other loads like lights, the generator will overload and trip (shutting off the lights). You may want to have the OFF switch for the charger conveniently accessible. I'd add the lighting and other planned loads to the generator for your test of the battery charger above.



Singinius said:


> I figure a photo may help clarify:
> http://www.flickr.com/photos/singinius/7626132024/


That helped me visualize! Let us know if it works out for you.


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## thingstodo (Jul 16, 2010)

Mike Leach said:


> Has anyone ever tried using a generator rated at the voltage equal to the battery voltage. This vehicle is a 36 volt, could you use a 36 volt generator or would there be an A/C to D/C problem?
> 
> I am just about finished my first conversion at 48 volts and was thinking about a 48 volt generator on board.


A DC generator would work (I think they were called magnetos. I have not seen one in a while), but without a charger involved, you could over-charge the batteries and reduce their useful life, or boil the electrolyte and ruin them (these are Absorbed Glass Mat - I think the electrolyte boils if the overcharge. There are vents that pop off)

An AC generator should have the AC converted to DC and regulated to charge the battery nicely - that's what the battery charger normally does. There *are* so-called 'bad-boy' chargers that simply have diodes to rectify the AC. I have no experience with them, but they kinda scare me and I would not use one if I had a choice.

The DC voltage that an AC generator output gets converted to with diodes and a capacitor or two is about 1.414 * the AC rated voltage. For your 48V batteries, that would be about 34V AC and that is not, as far as I know, a standard generator rating. Anything without a battery charger still has drawbacks about overcharging.

If it were my conversion, I'd use a 120V generator and a 48V DC charger plugged into it.


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