Zero Turn Radius Electric Riding Lawn Mower

I use 20 pc TS90ah in my mower and 1-1.5 hour is no problem

The mower: http://www.automek.com/evrider.php?page=1v

JRP3 said:

That might be a good application for a swappable pack so you don't carry around excessive amount of batteries. How many gallons of gas does a mower use in three hours? That should give you an idea of the kwhs you need in a pack.

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We actually did think about doing a hot-swappable pack. Lithium batteries where out of our price range and lead acids for us to get the projected run time were too heavy/big for the lawn mower. However, we were able to find a compromise in the middle that should allow us to run for about 1-1.5 hours.

When we calculated the battery pack size for the mower, we hit a fairly high number even for only the two hours we budgeted to run it. Our calculations showed for a two hour run time on a 30 degree slope going 5 mph we would need a battery pack size of roughly 8.5 kwhrs. This of course was for only a like 44 inch deck, not one of the massive 72" ones. The plus side of course is having a bigger mower means that it can support more battery weight.

Peter S said:

I use 20 pc TS90ah in my mower and 1-1.5 hour is no problem

The mower: http://www.automek.com/evrider.php?page=1v

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Nice! Those batteries must have cost something crazy though. At least the quote we got on them would have been more than the entire rest of the project. Also: BMS...ERRRRG!

TheRedBaron said:

Also: BMS...ERRRRG!

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Or not.....

Here is a copy of the calculations that we used to determine the amount of kwhrs we would need. Most of the numbers could easily be swapped for a different mower. However, you would still have to find how much power the blades alone would require to drive.

JRP3 said:

Or not.....

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True! It is nice to have a system that prevents your lithiums from exploding!

I've never seen a large format LiFePO4 cell exploding without a BMS. I'm running my CALB 100's with no BMS.

How do you then prevent under/over charging on the lithiums or a voltage imbalance on one cell compared to another? From my understanding of the situation, have over/under charged lithiums in series with each other can cause battery lifetime issues along with the potential to really screw up a battery(explosion may be a bit of a harsh term).

However, as a college student, I would say my hands on experience here is lacking. This is just what I have learned in the classroom and in research/talking with those who have dealt with lithium technology before.

So please, expand on this subject if you would! (why the electrical engineering department here does not have course on batteries is beyond me)

First step is to get a closely matched set of cells. Then balance them, either top or bottom balance the pack, benefits to each method, the more closely matched your cells are the less it matters which you use. Finally, don't charge or discharge them to the max, which you should avoid with or without a BMS to maximize life. If you want a simple monitor you split monitor both halves of the pack, any differences between halves denotes a problem.

My experience so far matches what JRP3 says. I quit top balancing my pack 9 months ago and only charge to 3.485vpc and haven't see the supposed drift people say will happen. Remember this is specifically with LiFePO4 cells, not other types. I haven't tested those. I found less than less than 1% of capacity is above 3.45V when the ending charge current is low.

If you are still looking for a solution to your 5v-0v-5v potentiometer issue look for some concentric shaft potentiometers here is a couple of links one to digikey and the other is a datasheet from farnell they make linear taper pots for guitar amps. You didnt say what resistance range you needed but farnell makes most standard ranges. If you use a concentric shaft pot you can wire one pot channel to vary resistance one way and the second channel the other direction and then use a SPDT relay connected to your reverse switch to change which pot channel has the input voltage. If you have any questions i can draw up a wiring diagram just let me know.
http://www.newark.com/jsp/search/browse.jsp?N=1001531+5094071&No=0&getResults=true&appliedparametrics=true&locale=en_US&divisionLocale=en_US&catalogId=&prevNValues=1001531&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D1001531%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_US%26divisionLocale%3Den_US%26catalogId%3D%26prevNValues%3D1001531

http://www.farnell.com/datasheets/576650.pdf

bennettdan said:

If you are still looking for a solution to your 5v-0v-5v potentiometer issue look for some concentric shaft potentiometers here is a couple of links one to digikey and the other is a datasheet from farnell they make linear taper pots for guitar amps. You didnt say what resistance range you needed but farnell makes most standard ranges. If you use a concentric shaft pot you can wire one pot channel to vary resistance one way and the second channel the other direction and then use a SPDT relay connected to your reverse switch to change which pot channel has the input voltage. If you have any questions i can draw up a wiring diagram just let me know.
http://www.newark.com/jsp/search/browse.jsp?N=1001531+5094071&No=0&getResults=true&appliedparametrics=true&locale=en_US&divisionLocale=en_US&catalogId=&prevNValues=1001531&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D1001531%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_US%26divisionLocale%3Den_US%26catalogId%3D%26prevNValues%3D1001531

http://www.farnell.com/datasheets/576650.pdf

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Thanks for the links, we have hit a dead end with the string potentiometers. We were looking at a couple small ones (1.5" draw, 5kohm) and they had a price tag of $325 - $365. Which is so far out of our budget it isn't funny. So I'll look into what you suggested and perhaps some of the linear actuating ones.

The farnells pots in the newark.c om link are the third one down they are around 9 dollars. What i had in mind would be to use a joystick stye actuator with a push button to actuate a relay that would send the reverse signal to your controller and also change which pot channel that was sending the 5v speed signal to your controllers. I think i know the controllers you are using I have some that operate like that and they came off of some surplus scotters.