# Capacitor Bank effects on drag racing golf cart



## athomas03 (Jul 13, 2011)

Searching and reading old threads about capacitor banks on EV's has left me unsure if they can help or how much they can help in my application.
I know golf carts have their own forums, they just aren't as in-depth as this. Golf cart drag racing is 1/8 mile and on the electric side there are classes, 48v, 72v, and outlaw basically....each event can vary. I'm running 72v, Odyssey PC925 batts, high speed motor, overall weight is 850 lbs with me in the cart. Speed is 51.2mph in 1/8, the cart will go 60-62mph just takes longer to get up to speed (1/4 mile).....60ft times are slow right now. I searching for a higher amp controller.....currently using Alltrax 7245...which limits me to 450amps and less torque than I need at the start....so other than changing controllers (which I am in the process of doing) or paralleling another set of batts($1080), I can try for an extra boost from a capacitor bank. It may help accelaration that way or in reducing voltage sag initially with takeoff. I don't care as long as it helps and doesn't move me out of the 72v class. I am going to try a 20,000 micro farad bank that was on ebay.....wire it parallel to my pack.....any thoughts.....pros/cons on this. Thanks for any help or other ideas. Adam


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## DIYguy (Sep 18, 2008)

You can always wire a direct bypass to 100% battery power..... 

Just make sure you have ur hand on the disconnect...


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## athomas03 (Jul 13, 2011)

Yes, I could do the controller bypass. But, I didn't want to deal with the safety issues. If you don't have a disconnect and the contractor welds shut.....runaway cart! Would be cheaper than a high amp controller, though.


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## DIYguy (Sep 18, 2008)

It was meant a bit in jest. That said, there is "a little truth in every joke"...that's what makes them funny. 

http://www.rechargecar.com/product/ev-ez-safe-disconnect


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## DIYguy (Sep 18, 2008)

BTW, don't waste your money on that Cap bank....


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## athomas03 (Jul 13, 2011)

DIYguy said:


> BTW, don't waste your money on that Cap bank....


Snake oil?? Won't improve performance? I know there are many ev folks who say this. My vehicle is so light, though......no help. Any other opinions?


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## frodus (Apr 12, 2008)

They'll help for maybe 1 second as they drain with your foot on the throttle. They're "OK" for capturing regen, but even that has yet to be proven.

The amount you'd need just wouldn't help a ton, and would take up a lot of space. 

You'd be better off switching to lithium, lightening the battery pack, and getting the higher discharge/recharge rates that come along with it.


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## athomas03 (Jul 13, 2011)

frodus said:


> They'll help for maybe 1 second as they drain with your foot on the throttle. They're "OK" for capturing regen, but even that has yet to be proven.
> 
> The amount you'd need just wouldn't help a ton, and would take up a lot of space.
> 
> You'd be better off switching to lithium, lightening the battery pack, and getting the higher discharge/recharge rates that come along with it.


Any recommendations as far as lithium goes for this type racing?


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## DIYguy (Sep 18, 2008)

Frodus is right... however, you have a decent set of pb cells that will discharge more than twice what you are using. I'm not against Lithium, in fact I own 38 kw of it, however, you need to first use what you have. You need a new controller...one that will allow u to apply higher currents. Right now, all lithium would do for you is shave a few percent due to less weight. 

After you have a controller that will dish out some higher power....then go for the Li. There are lots of choices.... depends on your wallet, and expectations. When you get into the world of racing.... it's all about exposing the next weakest item.

BTW, paralleling another set of batteries will only make u slower. Ur still limited by your controller and now ur heavier.


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## frodus (Apr 12, 2008)

athomas03 said:


> Any recommendations as far as lithium goes for this type racing?


How many amps are you pulling?

How many Ah are the batteries you're using now?

I can help with cells, I work with a company in WA state that has several flavors.


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## frodus (Apr 12, 2008)

DIYguy said:


> Frodus is right... however, you have a decent set of pb cells that will discharge more than twice what you are using. I'm not against Lithium, in fact I own 38 kw of it, however, you need to first use what you have. You need a new controller...one that will allow u to apply higher currents. Right now, all lithium would do for you is shave a few percent due to less weight.
> 
> After you have a controller that will dish out some higher power....then go for the Li. There are lots of choices.... depends on your wallet, and expectations. When you get into the world of racing.... it's all about exposing the next weakest item.
> 
> BTW, paralleling another set of batteries will only make u slower. Ur still limited by your controller and now ur heavier.


So true. If the batteries are good, go with a higher amp controller. Zilla, Soliton, or a high amp Kelly controller ought to do the job if it's series wound. For sepex, the options are more limited.


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## athomas03 (Jul 13, 2011)

frodus said:


> How many amps are you pulling?
> 
> How many Ah are the batteries you're using now?
> 
> I can help with cells, I work with a company in WA state that has several flavors.


At least 450 amps. Its still pulling 400 at the end of the race. I assume it will pull 925 amps if I had a controller that would allow it. That's what the Odysseys will send initially, AH 28 I think. That is close. 

Also, DIYguy, I spoke of parallel pack assuming I would get a high amp controller and also to refer to slashing voltage sag in half. You are right, the extra lbs without controller upgrade would be a waste.


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## athomas03 (Jul 13, 2011)

Yes series cart.


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## athomas03 (Jul 13, 2011)

Here are a few pics. 



















Just as an after thought. Can this cap bank assist my controller if I wire it on the controller side? Assist with ramp up rate or any improved performance (allow more amps to flow)??? Would it wire between the large terminals on my contactor or directly to controller B+ and B-?


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## frodus (Apr 12, 2008)

Yes, it could help, but I don't know how much a 20000 uF pack would help.

If it's cheap, get the caps and try it.


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## Stiive (Nov 22, 2008)

I wouldnt get the caps in this case, i think its probably a waste of money. I think the lead acid batteries would survive without the caps. When the voltage to the motor is low and current is high during initial acceleration, the voltage sag doesnt really matter as its getting chopped anyway.

If your only interested in acceleration, then i would go lithium as the weight saving would be huge and after all, your acceleration = force/mass. To get double the acceleration you can either halve your mass, or double the force to the pavement. Sometimes its cheaper to reduce the mass. You'd have to work out what percent increase of force (torque=radius of tyres x force) you were going to get with these capacitors vs the increase in mass to see if its even worth it.

I would say your carrying around too much capacity (28Ah) anyway for doing a 1/8 mile run. Run a couple of strings of the A123 cells in parralel to get the excact amount of capacity and peak power you require.


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## athomas03 (Jul 13, 2011)

frodus said:


> Yes, it could help, but I don't know how much a 20000 uF pack would help.
> 
> If it's cheap, get the caps and try it.


I gave them a try, the results are very unofficial......60ft times very similar 2.6sec range with and without cap bank. The voltage sag appears to be 2 volts different, though. Without caps the voltage drops from 78v to around 62v before coming back up and with caps it was more like 64v. So, maybe it helps slightly. I tried it on the parallel to pack and also on controller side. I think B+ and M- would be ideal place to combat voltage sag, but I have to unhook and recharge everytime. So, parallel to pack is easier (must use pre charge resistor) and it charges with the pack.


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## frodus (Apr 12, 2008)

is that 2 volt difference repeatable? after charging in each case?


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## athomas03 (Jul 13, 2011)

It was repeated once. I will test some more this week. It makes me wonder if a larger cap bank would have more of an effect.


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## frodus (Apr 12, 2008)

you should be able to see some difference.

Like, Charge fully, connect capacitors, use the same straight away, mash the throttle, record voltage drop, let off throttle, take home, disconnect the caps, recharge completely, then repeat without. 

Repeat a few times so you have good data. Sometimes data can be a fluke. Just make sure it's at the same state of charge, i.e. both times are fully charged.


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## electrabishi (Mar 11, 2008)

athomas03 said:


> Here are a few pics.
> 
> 
> 
> ...


Adam,
for only 1/8th mile racing and running lead acid I'd definitely switch to the PC680's. At 15 lbs each they will still put out nearly 1000 amps for 10 seconds. The PC925's will do it easier but for a 72V pack you would save 66 lbs in going with the PC680 (at 90 lbs pack) vs the PC925's (156 lb pack). So if you are on a budget you can't beat the PC680 for power density. And for $100 each its a lot less expensive than Lithium. However if you want to go to lithium for a 72V pack, may I suggest you look for a supplier of the Headway 38120-P cells. Testing I did with them shows they's do 400 amps for 12 - 14 seconds and 540 amps for 3-4 seconds. I would venture to guess (since I've spec'd out junior dragster packs) that you could probably go with two strings (for 800 amps) of 22 cells. If you wanted to be easier on the cells you could go 3 strings. 44 cells of 38120-P's at ~$15 each would cost $660 and weigh 29lbs, but you would be pushing those cells right to the limits. A safer approach (comparable to the PC680's) would be 66 cells (3 strings of 22) at ~$15 each would cost $990 and weigh 43.5 lbs.

So you can see that the Headways would cost a little more, but probably not much more than 6 of the PC925's that you already have. And the Headway's compared to the PC925's you'd shave over 100 lbs.

On another note, if you are looking for more current may I suggest you look for a supplier for the Logisystems 72V, 1000A controller. These can be had for the same price you can get the Altrax 7245 (~$650). I have run one of these on a 400 lb Junior Dragster and now it is on my mini chopper pit bike. I've swapped in an Altrax 7245 but the 1000 amps from the little Logi beats it all day long.

Just a few thoughts.

Mike


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## athomas03 (Jul 13, 2011)

electrabishi said:


> Adam,
> for only 1/8th mile racing and running lead acid I'd definitely switch to the PC680's. At 15 lbs each they will still put out nearly 1000 amps for 10 seconds. The PC925's will do it easier but for a 72V pack you would save 66 lbs in going with the PC680 (at 90 lbs pack) vs the PC925's (156 lb pack). So if you are on a budget you can't beat the PC680 for power density. And for $100 each its a lot less expensive than Lithium. However if you want to go to lithium for a 72V pack, may I suggest you look for a supplier of the Headway 38120-P cells. Testing I did with them shows they's do 400 amps for 12 - 14 seconds and 540 amps for 3-4 seconds. I would venture to guess (since I've spec'd out junior dragster packs) that you could probably go with two strings (for 800 amps) of 22 cells. If you wanted to be easier on the cells you could go 3 strings. 44 cells of 38120-P's at ~$15 each would cost $660 and weigh 29lbs, but you would be pushing those cells right to the limits. A safer approach (comparable to the PC680's) would be 66 cells (3 strings of 22) at ~$15 each would cost $990 and weigh 43.5 lbs.
> 
> So you can see that the Headways would cost a little more, but probably not much more than 6 of the PC925's that you already have. And the Headway's compared to the PC925's you'd shave over 100 lbs.
> ...


Thanks for the input Mike. The Alltrax 7245 was used one, only $250 and it allowed my to go from 36 to 48 to 72. I intended on buying a Logisystems, though in the future, but I waited a couple months too, late and they shutdown production. Maybe they will come back, in the meantime I may just bypass until I can find a high amp controller. 
Didn't realize the lithiums were that affordable...this is good info on the # of strings to achieve the amperage I might be using. Yes, the 680's are also a popular choice, lighter, although I thought they were only 680 amps....most guys parallel two sets if they use these. 400lbs.....wish I could get that light, my cart is around 665lbs without me in it. Adam


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## ElectriCar (Jun 15, 2008)

Have you gotten a new controller yet? Here's why I ask. I had a 10000uf bank at the controller input side, within a foot. I've used it since I ran lead, since upgraded to lithium pack and left them in place.

I removed them today and noticed what seems to be a much more lethargic takeoff than before. With them installed, when I hit the throttle, even slightly it would lurch forward and chirp the tires. So driving home today I hit the throttle a little heavy a few times and again it seems lethargic compared to before. 

In your case you'll probably need a controller with the acceleration rate reduced to basically nothing. THIS is where you get your hole shot, instant full throttle to the motor. With the cap bank at the controller, when you dump the throttle with a modified controller (that's how mine is) you dump the battery capacity in there along with the cap bank. The cap bank will reduce sag just as you said which will force more amps through the motor as voltage is what forces current to flow, more of it and you have more current flow. I too noticed mine sags further now than with them by two volts as well. 

Of course it may be all in my head but I don't think so. The key though is you have to reduce the accel time in your controller, whatever controller you have, to maximize your hole shot. If the caps give you more torque a little faster then you've gained a little more edge. 

Again, your trials before with no detectable difference was likely due to your controller being unable to dump power fast enough to overcome the capacity of the batteries to deliver. Fix that and I suspect you'll see a big difference when you first hit the throttle, if it doesn't flip you over!


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## bjfreeman (Dec 7, 2011)

frodus said:


> Yes, it could help, but I don't know how much a 20000 uF pack would help.
> 
> If it's cheap, get the caps and try it.


the maxiwell 56fd (yup farads) 16 volt pack
is 200 amps for 1sec continoush 12 amps
you hve to have many 
http://www.maxwell.com/products/ultracapacitors/docs/DATASHEET_BMOD0058_E016_B02_1015371.PDF
they are pricey so you looking at $10K or more.

The advantage is quick charge and over 10yrs of cycling.


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## Sunking (Aug 10, 2009)

Sorry I have not read all the replies so I do not know if anyone has addressed this or not. I have modified a few golf carts. Currently I have one for showing off and racing, and another for a NEV/golf cart.

You mentioned adding an extra parallel battery bank to lesson the effect of voltage sag. You alo mention using an Altrax 7245 controller which means you are using a series wound DC motor.

With that said acceleration or torque does not come from voltage, it comes from current. In series wound DC motor current and torque are proportionally related and inverse to speed. Voltage is where you get the RPM and RPM is proportional to voltage. And oddly enough current and voltage are inversely proportional so the faster you go the less torque and current.

So if you are looking for better acceleration, especially at the low end, you are looking for current, not voltage. Knowing that you can attack it with parallel controllers, larger cables, paying special attention to connection resistance, and lastly and most importantly using batteries with low internal resistance like AGM or even better NiCd.

So adding a parallel battery will lower internal resistance but any gain will be lost to extra weight.

Hope that helps and good luck.


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## Guest (Dec 18, 2011)

20 AH A123 Pouch Cells at like $25 each would be the bomb for your cart. High amperage output. So for a cool guaranteed 18 AH pack at 72 volts and maximum of about 10C out put you could be the one to beat. $575 bucks for a pack and you can charge it up quickly and then run again and again and again. You will be only carrying a tiny amount of weight and it will just haul butt. I assume your not concerned about distance. Just a trip or two down the track for fun at a time. Maybe double up and do a 36AH pack and get a few more trips down the track before you need to recharge. Price is good and the cells will be far better than any lead acid. Yes you need a good fast way to charge and a good controller that will belt out the amps. Perfect for such a light weight vehicle. 

Pete 

PS: Don't bother with caps.


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## athomas03 (Jul 13, 2011)

Yes, I did get another controller. It bumped me up to 750amps in race mode. I had a bypass switch that I used just after takeoff for max amps (HD disconnect, also) off the line. 

























Best 1/8 mile was 10.50 and best speed in 1/8 was 57.41 mph.

Making plans now for 2012.


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## Jayls5 (Apr 1, 2012)

The type of capacitors you suggested would likely be far too little capacitance to accomplish anything. They do reduce voltage sag, but usually only when properly sized.

http://web.mit.edu/scolton/www/everpres.pdf

Here's a MIT paper on an ultracapacitor assisted go-kart. It uses a SEPEX motor, huge maxwell super-capacitor, and it has circuitry specifically designed to alternate between the batts and caps depending on charge to make it worthwhile.


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