Lithium battery for a ball machine

[Chas Tennis]

Battery cost
http://dx.com/p/trustfire-protected-...pack-blue-5790

[retrograde]

Here's an 18ah Lipo battery designed for 12V applications made by Shorai:

http://www.batterystuff.com/powerspo...18A1-BS12.html

Weighs only 2.12 lbs. Compare that with the PowerSonic which weighs 13 lbs. Note the Shorai has smaller dimensions than a standard 18ah SLA battery and comes with some foam inserts to help with fitment. I might be tempted to make some shims.

It looks like the Shorai has NB connectors. The Lobster Elites use F2 connectors, not sure what the Grand Elites use - but you can buy adapters from any battery shop.

I am an electrical engineer but have not done due diligence on this battery (I have the flu and am about to pass out!). At least you now have something to Google on and see what other people are saying about this battery. I suspect this battery either has a regulator on it, or the per cell voltage of SLA and Lipo are similar enough where it's not a problem. I also would look into whether this battery has a circuit which shuts off the battery if the per-cell voltage drops too far ... it might not be needed if you can get a "feeling" for when the battery votage has dropped too far.

Note you'll have to get a Lipo-specific charger. You'll also need to read up on the care and handling of Lipo batteries - they are different from SLA. Lipo's have very low self-discharge so you can let them sit for long periods of time unused. That means you shouldn't leave your Lipo charger connected during storage.

p.s. If you live in a hot climate like Andre Agassi, or leave your ball machine in a hot car, that might explain some of the life problems with your first SLA battery.

[retrograde]

Originally Posted by Chas Tennis

Battery cost
http://dx.com/p/trustfire-protected-...pack-blue-5790

When using small diamater batteries, one needs to make sure the battery can supply the current the application needs. The PowerSonic SLA can output a max of 54 amps. The trusfires have a capacity of C = 2.5ah ... if their current output is, as an example, 20C, the the current output would be 20 * 2.5 = 50 amps.

I guess your friend has tried this already, but just more due diligence before spending you money.

Here is an example of what radio controlled race car hobbyists used ... note this has a hard shell case, not like the soft (and easily damaged) cases the model airplane guys used:

http://www.amainhobbies.com/product_...FQKRPAodW14A2A

[retrograde]

Originally Posted by BoingTennis

Topspin, I don't think we will find a lot of feedback on these batteries being used with ball machines.

I find this to be a worthy project to try, since my Lobster is in need of a replacement battery anyway. I myself do not live in the US, and that is the more reason for me to buy these LiFePO4 batteries since they are so light, shipping it to Asia would be cheaper.

After I did some google research, these are some of my findings:
1) This battery type will most likely work very well with our ball machines. They have been used extensively in many applications including automotive, EV, etc. Both high-discharge and sustained-discharge types of applications have been covered.
2) Some batteries has better electronic features than others. Shorai batteries (big with motorcycle owners) does not seem to have as much built-in protection and balancing features as the batteries from Powerizer.
Battery balancing feature seems to be an important one to have.
3) Price varies greatly and it looks like it depends on the electronic features I mentioned above.
4) Our stock charger (for Lobster owners) which are most likely made by Soneil are save to use with the LiFePO4 batteries. Pulse mode charging in the Soneil will only function when the battery is at 0.5V-5V. LiFePO4 batteries are not supposed to be discharged below 10V, so our charger will never have its pulse mode charging activated. Soneil charger highest charging voltage is 14.7V, which is below the max charging voltage for LiFePO4 batteries (15V).

Here are the alternatives (for Lobster owners) 7.13L x 3.03W x 6.57H:

1) Shorai 18Ah 5.83L x 2.60W x 4.13H
Only 2.12 lbs, prismatic cells, smaller than stock Lobster battery, same capacity as stock, doesn't seem to have built-in protections/balancing.
2) OEM Battery from BatterySpace with Balancing
7 lbs, prismatic cells, same size as the stock Lobster battery, 20Ah capacity, has balancing PCB but no built-in protection.
3) OEM Battery from BatterySpace w/o any extra features
6.6 lbs, prismatic cells, same size as Lobster battery, 20Ah, no balancing/protection, cheapest I've found.
4) Powerizer w/built in protection and balancing (PCM)
7lbs, cylindrical cells, same size as Lobster battery, 20Ah, complete built-in balancing and protection, expensive.

I'm going with option #2. Will purchase today and will probably get it within 3 weeks. I'll snap some pictures and test it ASAP.

I didn't see you excellent post! I like Shorei because they are made in Japan. But I think having a balancing circuit and protection (is that for overcharging or too low a discharge voltage?) are very useful. Then again, my model airplane friends tell me Lipo cell balancing isn't as much a problem as it used to be.

[Chas Tennis]

Originally Posted by retrograde

When using small diamater batteries, one needs to make sure the battery can supply the current the application needs. The PowerSonic SLA can output a max of 54 amps. The trusfires have a capacity of C = 2.5ah ... if their current output is, as an example, 20C, the the current output would be 20 * 2.5 = 50 amps.

I guess your friend has tried this already, but just more due diligence before spending you money.

Here is an example of what radio controlled race car hobbyists used ... note this has a hard shell case, not like the soft (and easily damaged) cases the model airplane guys used:

http://www.amainhobbies.com/product_...FQKRPAodW14A2A

In the picture on the link, the batteries looked a little smaller in diameter than I remembered them. I am checking the part number that he gave me. I was surprised at the way the Tennis Tudor ran, it seemed normal in power.

[jam54]

Wow, Top Spin....looks like a touched a nerve. I have no agenda, just a lot of experience with tennis ball machines. And sorry if I have a brand preference. Most do.

You make some valid points regarding draining batteries. The biggest enemy of SLA batteries is to be completely discharged. But I still think you are in the minority based on the amount of time you are on the court with a machine. If the majority of ball machine users played for 4 hrs or drained the battery like you do, ball machine companies would quickly see the current 18Ah SLA batteries they use as inadequate.

I don't quite understand why an external battery pack is such a bad option, esp. given the limited alternatives. But good luck to you finding one.

[IdrinkYourMilkshake]

Just put the big battery in. 35 cold cranking amp hours!!

[retrograde]

Originally Posted by IdrinkYourMilkshake

Just put the big battery in. 35 cold cranking amp hours!!

Is this the battery you were connecting to externally before? What mods did you need to make to your SP Lite to carry it internally? Or maybe that's the stock battery size for the SP Sport so no mods needed?

[IdrinkYourMilkshake]

^^ Correct, this was the external battery. It lasts me close to 6 hours because I have automotive relays on the after-market remote that shuts down the motors when I pick up the tennis balls and make sure I don't waste the power. This is originally a Silent Partner Lite machine. There are a couple vertical tabs at the edge that need to be cut in half as seen in the picture and the opposite side has two vertical tabs that need to be removed. I put padding in the well of the stock battery footprint that sort of cushions the big battery.
Drill two holes on each end for an aluminum bar, drill holes, screw and nut, leave loose while looping the straps around, pull tight. Then tighten the aluminum bars down flat to the plastic base. It's pretty solid. I'm going to finish this today and put in a new mode so I can push a button on the remote to eject just one ball and stop.
I have a 4 button remote. Motors on/off, Ball Feed on/off, Oscillate on/off, One-shot ball feed.

[Bolivian10s]

That looks heavy, will your machine support the weight and not crack your plastic case?

[IdrinkYourMilkshake]

Originally Posted by Bolivian10s

That looks heavy, will your machine support the weight and not crack your plastic case?

Doesn't look like it. The blue cover adds a lot of integrity, but I'm going to make it so the cover lifts on and off so the machine doesn't need to be put on the side to take the cover off. No doubt the machine can't be dropped even a little bit. The convenience of not carrying an external battery with plenty of capacity is worth it.

[retrograde]

Originally Posted by IdrinkYourMilkshake

I'm going to finish this today and put in a new mode so I can push a button on the remote to eject just one ball and stop.
I have a 4 button remote. Motors on/off, Ball Feed on/off, Oscillate on/off, One-shot ball feed.

I think there was someone with the handle "rjw" who described some SP mods to add 3rd-party remote funtionality. As an electrical engineer, I'm intrigued. Is there a thread that discusses the mods?

[mctennis]

Originally Posted by jam54

Regarding batteries for tennis ball machines: SLA (sealed-lad acid) are still the most practical and affordable option. Lithium batteries are very expensive and may not work with all applications.

Ultimately, battery life and effectiveness has more to do with the owner's
charging procedure than the type of battery used. Depending on the type of charger, an 18Ah lead acid battery will last 3-4 years with normal use and provide over 2 hrs of playing time on a charge. I think it's pretty unusual for any individual to use a ball machine for more than 2 hrs at a given session unless you a teaching pro.

But a battery is only as good as how it is charged. Most ball machine companies, such as Tennis Tutor, only use "smart" chargers. Smart chargers
will not overcharge the battery (one of the enemies of batteries) and make it
very convenient to recharge. If a machine is inactive for a long period and not charged, batteries will deteriorate -- another reason smart chargers are effective to prolong the life of lead acid batteries.

There is always the chance of getting a "bad" battery but that is pretty rare. So ultimately, I think the answer is to follow the charging procedures and not try and reinvent the wheel.

Ditto on these comments. Check with the manufacturer about what they also recommend. At times we out think what we should do. Simple is better at times. I replaced my Tennis Tudor battery by the recommendations that Tennis Tudor actually suggested to me. I could have bought one from them but they also suggested another place to get one locally. Great service from Tennis Tudor!!

[IdrinkYourMilkshake]

Originally Posted by retrograde

I think there was someone with the handle "rjw" who described some SP mods to add 3rd-party remote funtionality. As an electrical engineer, I'm intrigued. Is there a thread that discusses the mods?

I think I remember that thread...the guy basically made a new board for it and put a linear actuator in like the top version would have. All I did was put the simple remote in with some added wiring for indicator lights and relays and of course the big battery now. I was thinking about a CD Deck/MP3 player, but I ain't got time for that. Here's a link to the unit I put in, but I got it off bay for like 12 bucks.
And I just want to say Silent Partner is a great company and makes a great product, I just love tinkering with stuff.

[IdrinkYourMilkshake]

Finished this thing. The 35ah battery isn't as heavy as I thought it would feel. The red light goes out when the wheels are spinning and the green light comes on when the ball feed is running.

[retrograde]

Originally Posted by IdrinkYourMilkshake

I think I remember that thread...the guy basically made a new board for it and put a linear actuator in like the top version would have. All I did was put the simple remote in with some added wiring for indicator lights and relays and of course the big battery now. I was thinking about a CD Deck/MP3 player, but I ain't got time for that.

Very nice and useful mods. Built in boombox would be unique for sure

Do you have a link for the relays? It sounds like you wired them up into a harness rather than onto a separate board? I'm curious how difficult it was to figure out where to connect the relays to the existing board(s). I've never opened up a SP machine or seen their boards.

[IdrinkYourMilkshake]

Originally Posted by retrograde

Very nice and useful mods. Built in boombox would be unique for sure

Do you have a link for the relays? It sounds like you wired them up into a harness rather than onto a separate board? I'm curious how difficult it was to figure out where to connect the relays to the existing board(s). I've never opened up a SP machine or seen their boards.

It's a standard 12v automotive relay, 2 of the them, something like this.

In this picture you can see them in the lower right. The way it's wired is, start at the big rocker power switch on the panel, it controls two circuits when switched and just run wires off those connections. I made a wiring harness of sorts with plugs so it could be removed and put back to factory specs. The relays just do exactly what that big rocker switch does and the switch on the panel still works too.

[jam54]

I'm surprised that some of you are so insistent on putting essentially car batteries in your machine. Portable machines like this are designed to be, well....portable. Which means light enough to easily transport. What good is it to have a machine that gives you 10 hrs of playing time if it weighs 70 lbs and collapses under it's own weight?? Or try and put something like lithium batteries that cost so much more and may have other issues? The majority of ball machine users are on the court for 2 hrs or less. Sure there are exceptions, like teaching pros, but again, they represent a small percentage.

Keep your SLA battery and charge it properly and you'll be fine.

[IdrinkYourMilkshake]

Originally Posted by jam54

I'm surprised that some of you are so insistent on putting essentially car batteries in your machine. Portable machines like this are designed to be, well....portable. Which means light enough to easily transport. What good is it to have a machine that gives you 10 hrs of playing time if it weighs 70 lbs and collapses under it's own weight?? Or try and put something like lithium batteries that cost so much more and may have other issues? The majority of ball machine users are on the court for 2 hrs or less. Sure there are exceptions, like teaching pros, but again, they represent a small percentage.

Keep your SLA battery and charge it properly and you'll be fine.

I agree with you on lithium batteries, but a 35ah SLA is not a car battery, it's about as big as you want to go though on a plastic framed machine. It's no where close to collapsing. Some of us want to be out there all afternoon with breaks in between.

[retrograde]

That Powersonic 35AH battery weighs 25 lbs. Typical car batteries weigh 40-50 lbs depending on the group size.

The "standard" batteries used by SP and Lobster Elite are 18-20AH and weigh around 13 lbs. The SP Lite/Lite-R come with a smaller 7-8AH battery that weighs around 6 lbs (and I believe you can upgrade the Lite/Lite-R with the larger 18-20AH battery).

I think folks who have their own court or nearby court can wheel around a 50-60lb ball machine. For people like me who have to drive to a court, portability/weight is more of a consideration. I ended up building a ramp using two 6'x10"x1" wood boards so I can easily roll any SP or Lobster Elite sized machine into the back of my wagon.