Need some advice on LifePO4 batteries for my scooter

[Windmaker]

I have a previous post on this forum seeking info on extending the range of my 3 wheeled mobility scooter (48v system = 4 x 12v/20ah SLA batteries) by adding ah extra set of SLA batteries. Lithium batteries entered into the reply exchanges and I haven't been able to shake the interest it provoked for me since then. Let me say first that it appears that LifePO4 batteries are probably the best selection from the existing array of Lithium chemistry types for my desired use at this point in time, especially because of their superior stability (safety), longevity, etc.

One of the previous replies to my former post was that even a 10ah Lithium battery would surpass the capabilities of my SLA batteries. However, when I questioned an ebay seller about his 48v 15ah LifePO4 battery description having a comment that it was compatible with a 500w motor only, I asked if he sold a battery that would be compatible with my 800w motor. He replied by recommending a 48v 20ah LifePO4 battery (which by the way is considerably more expensive than the 15ah batteries).

In summary, is there anyone who would care to offer comments on what amperage rating would suffice as a replacement for my scooter's SLA battery power with LifePO4 battery power? In other words, do I need the 20ah LifePO4, or would a lower amperage be adequate even though the distance range wouldn't be as good?

Is my existing controller unit compatibility affected by the amperage rating of the battery, or is the voltage the only thing that matters?

 

[Sunder]

Batteries have both a capacity (energy), and a power rating. Many LiFePo4 batteries are designed to be energy dense, rather than power dense. These cells typically cannot be discharged at a rate which would drain the capacity in less than 1 hour, otherwise known as "1C", or 1 Capacity.

So your 10Ah battery, discharged at 1C, would be 48v x 10A = 480w, ideal for 500w motors.

A 800w motor, would require a battery that could deliver at least 800w / 48v = 16.66a. So a 15Ah battery might be pushing it. It might seem to work okay, but you would be shortening the life of the battery.

A 20Ah battery would be safe, and probably has more profit margin for the seller, hence he's recommending the larger one. Personally, I would not buy the 10Ah one, and would only consider the 15Ah one if money was an issue. After all, you don't always use the full 800w available, right? Mostly just when you start, and go up hills. Short bursts of ~1.1C rate won't shorten the life that much.

 

[Windmaker]

Sunder ~
Thank you tremendously for your impressively complete and educational answer. In fact, I'm a bit beyond impressed...closer to astonished or astounded. Replies just don't come any better than yours. Case closed! :lol:

 

[Rassy]

Pretty much agree with what Sunder said.

I'm going to guess you don't have a Watt meter, but because you said you wanted more range the bigger (AH rating) the battery the better. If you don't push your scooter too hard (speed and steep hills) you might be getting close to the rating of the SLA batteries.

Here's an easy way to tell how much of the battery you are using: Start with fully charged batteries. At the end of the ride charge the battery. If your charger is a 2AH charger just multiply the hours required to charge the battery by 2 to obtain the AH you used. Likewise, if your charger is a 3AH charger then multiply by 3, etc.

This won't be real accurate, but it will give you a good idea of the size of battery you should get. In other words, if you take a ride and use about 12AH, then a 15AH battery would barely be adequate for the same ride, since it's better not to run the battery clear to empty.

 

[Windmaker]

Pretty much agree with what Sunder said.

]I'm going to guess you don't have a Watt meter, but because you said you wanted more range the bigger (AH rating) the battery the better. If you don't push your scooter too hard (speed and steep hills) you might be getting close to the rating of the SLA batteries.

Here's an easy way to tell how much of the battery you are using: Start with fully charged batteries. At the end of the ride charge the battery. If your charger is a 2AH charger just multiply the hours required to charge the battery by 2 to obtain the AH you used. Likewise, if your charger is a 3AH charger then multiply by 3, etc.

This won't be real accurate, but it will give you a good idea of the size of battery you should get. In other words, if you take a ride and use about 12AH, then a 15AH battery would barely be adequate for the same ride, since it's better not to run the battery clear to empty.

Thanks for the reply Rassy. That's the first I've heard about the "rule of thumb" method of calculating how much battery I'm using. I'll have to give that a try tomorrow or as soon as I am able. In the meantime I've attached some pics of a LifePo4 48v 15ah battery I'm watching on ebay at auction. In the last two months this particular battery has been sold for under two hundred dollars several times, and that's a heck of sight better than the $350 to $700+ prices I find for 48v 20ah LifePo4's, so if the only real negative is that it won't last as long (recharge cycles) then it may be worth the sacrifice. As for speed, I do generally run at max speed on the street (13mph...advertised 15 mph), but I am in a coastal area with no hills or significant inclines to be concerned about......although I have to admit I'm a heavy rider load (close to 300 lbs.). Despite the advertised "up to 40 miles range per charge", the real life fact is that I'm getting less than 20 miles per charge with my brand new scooter with 4 12v 20ah SLA batteries. Unless my understanding is off, I think even the 48v 15ah LifePo4 will get a range significantly past that mark....or at least I hope so....if not, I'd be wasting my money.

Simply put, my choice at this point in time is whether to add another set of SLA batteries wired in parallel, or to switch to the lighter, longer lasting, and farther range LifePo4 batteries. I would love to know what kind of range the LifePo4 would give me. It would certainly help in making my decision.

The auction for that battery ends in one day plus about twenty hours, so I don't have long to wait. It seems these sellers are now mostly going to reserve prices so as to not let their battery packs be sold to cheaply. The sale I'm referring to is without reserve and I'm hoping to make a low cost purchase.....if I am going the LifePo4 route now.

P.S. - No, I don't have a watt meter

 

[Rassy]

Windmaker, your comment about possibly 'wasting your money' caught my eye. You probably already have this all figured out, but since your SLA batteries are new and apparently working okay, I would just leave them as is and when you get your new battery, assuming you have a place to also carry it on the scooter, add a power plug to it so you end up having a choice of running from the SLA or from the LiFeP04.

This would definitely increase your range and at the same time let you get good use from the LiFePO4 even if it isn't all you were hoping for.

Just as a side note, I would not run the different chemistries in parallel. I think you can find discussions on this somewhere in the forum.

 

[Windmaker]

Windmaker, your comment about possibly 'wasting your money' caught my eye. You probably already have this all figured out, but since your SLA batteries are new and apparently working okay, I would just leave them as is and when you get your new battery, assuming you have a place to also carry it on the scooter, add a power plug to it so you end up having a choice of running from the SLA or from the LiFeP04.

This would definitely increase your range and at the same time let you get good use from the LiFePO4 even if it isn't all you were hoping for.

Just as a side note, I would not run the different chemistries in parallel. I think you can find discussions on this somewhere in the forum.

Bingo!.....Now there's an idea that hadn't occurred to me. I think there would be space in a compartment under the seat for the battery pack (and I would just have to pop the seat up to charge the LifePo4 pack, but the alternate connection(s) set up to my controller/motor may pose a significant obstacle. Being of different chemistries the two power supplies would, I think, most probably have to be separated entirely, and therefore I'm suspect of how convenient a transfer method from one power supply to the other could or would be. Sounds like a job for a knowledgeable electrician to me.....if it's possible at all. Thanks for the suggestion in any case.

 

[Rassy]

Actually, switching from one battery to another could be as simple and basic or as sophisticated as you desire.

Somewhere in the wiring of your existing batteries there should be a connector that is between your batteries and your controller. Pictures may be required if you can't find this connector yourself and you will want to check it with your DVM (Digital Volt Meter) to verify that it is indeed the 48 volt supply line. Then you will need to purchase the same connector to put on the new battery and you are good to go, being able to plug either battery into the system. If you follow what I just wrote here you are good to go. If not, get some local or forum help.

For charging the batteries, the sure way is to have the SLA's hooked up when using the SLA charger and the LiFeP04 disconnected when using it's charger, but depending on the wiring arrangement this might not be important. One nice thing about a setup like this is that you can be charging both batteries at the same time.

A more sophisticated solution would be to install a marine battery selection switch between the two batteries, which would eliminate the need to disconnect/connect the desired batteries at the connectors. But this would necessitate verifying that the charging circuits are independent.

https://www.amazon.com/Perko-8501DP-Marine-Battery-Selector/dp/B00144B6AE/ref=sr_1_1?ie=UTF8&qid=1478232331&sr=8-1&keywords=perko+marine+battery+switch

 

[Windmaker]

Rassy......Don't forget that you're speaking to "grasshopper" here (Novice, that is) when it comes to electricity and batteries. Kidding aside, I think that I do get most of the drift of what you're saying at a minimum. One of the "obstacle" issues I referred to was adjusting the wiring and putting whichever transfer switches (that were finally adopted) at a location that was convenient to access when the time came to switch battery packs. Perhaps that could be done by drilling new holes and running wiring into that compartment under the seat where I intended to locate the second battery pack (either SLA or LifePo4) and then the only task would be lifting up the seat (after unlocking with the key) to access the transfer switch...for an added LifePo4 that is. I could probably even attach the switch to the (plastic) wall of the compartment, if necessary. In any case I appreciate your suggestions and other remarks ....they've been a big help. Now I'll have to wait to see if I can purchase that ebay battery at a low enough price to take the leap.

 

[Windmaker]

Just a note that even generic low-power LiFe should be capable of 3C peak (~1500W if pack is 48V10Ah). As before, cut your SLA Ah in half to replace it with vastly superior lithium. (20Ah SLA <10Ah lithium)

Thanks eTrike....I do recall your assertion above from the other thread. That's why I was a bit confused when I saw the math from Sunder that indicated my 800w motor would need more than even a 15ah LifePo4 would provide ("800w / 48v = 16.66a. So a 15Ah battery might be pushing it."). And to be frank, I'm still a bit uncertain as to what I'm missing here, except to say that I gather that a 15ah Life Po would be sufficient for my scooter at perhaps the sacrifice of a having a shorter life span than if I had a lower watt motor......correct? I do wonder how much shorter.

 

[Sunder]

I'm still a bit uncertain as to what I'm missing here, except to say that I gather that a 15ah Life Po would be sufficient for my scooter at perhaps the sacrifice of a having a shorter life span than if I had a lower watt motor......correct? I do wonder how much shorter.[/color]

Correct. Almost all cars on the road are capable of 200km/h, but while a Ferrari will survive the Le Mans 24 hour race, do you think your average Kia will?

What happens is that every battery has an internal resistance rating. The higher that internal resistance, the more heat the battery generates at a fixed load. The more heat a battery generates, the shorter its life.

Unfortunately, there is no industry standardised method of translating this to a recommended maximum current draw. Two resellers can rate the exact same cells as 1C or 3C. It could be that one is intending to offer a 3 year warranty, and the other is intending to fight/stall/evade every warranty claim.

The other thing you might not know, is whether the reseller has installed a 10amp BMS into the 10Ah battery pack, and a 15amp BMS into the 15ah battery pack, etc. Unlikely, but if he did, then your battery would work fine most the time, but every time you try to go up a steep hill, the battery cuts out to protect itself...

Anyway, the proverb that comes to mind here is "buy cheap, buy twice". If you can afford the 20Ah battery, its safest. If you can't the 15Ah is almost certainly okay. The only battery I wouldn't recommend is the 10Ah battery, because even if it's "capable" of 3C (30A, or 1440w), not only will you be shortening its life, you'd probably be voiding the warranty now that he knows your application.

 

[999zip999]

You don't have to use those SLA look a like 12v lifepo4 batteries to from a 48v 15ah or 20ah batteries. You can buy a 48v 15 or 20ah lifepo4 battery. One bms for the the battery not four bms's and 4 inter connections. What's the size of your battery compartment and the spec's on the controller as that is the most important info on deciding on the proper battery needed with some head room so it would last. Do not run the battery at its limits as a rule.

 

[999zip999]

A lot of cheap crap on ebay. Most people go to eBay or one of the other websites buy their battery have a problem and come to ES afterwards and then tell us what the ad said on the website. Bull.

 

[Windmaker]

I'm still a bit uncertain as to what I'm missing here, except to say that I gather that a 15ah Life Po would be sufficient for my scooter at perhaps the sacrifice of a having a shorter life span than if I had a lower watt motor......correct? I do wonder how much shorter.[/color]

Correct. Almost all cars on the road are capable of 200km/h, but while a Ferrari will survive the Le Mans 24 hour race, do you think your average Kia will?

What happens is that every battery has an internal resistance rating. The higher that internal resistance, the more heat the battery generates at a fixed load. The more heat a battery generates, the shorter its life.

Unfortunately, there is no industry standardised method of translating this to a recommended maximum current draw. Two resellers can rate the exact same cells as 1C or 3C. It could be that one is intending to offer a 3 year warranty, and the other is intending to fight/stall/evade every warranty claim.

The other thing you might not know, is whether the reseller has installed a 10amp BMS into the 10Ah battery pack, and a 15amp BMS into the 15ah battery pack, etc. Unlikely, but if he did, then your battery would work fine most the time, but every time you try to go up a steep hill, the battery cuts out to protect itself...

Anyway, the proverb that comes to mind here is "buy cheap, buy twice". If you can afford the 20Ah battery, its safest. If you can't the 15Ah is almost certainly okay. The only battery I wouldn't recommend is the 10Ah battery, because even if it's "capable" of 3C (30A, or 1440w), not only will you be shortening its life, you'd probably be voiding the warranty now that he knows your application.

Sunder, you're quite a fellow there mate. Once again I am inordinately impressed with the quality of your remarks. Needless to say, I appreciate them. As for the affordability issue, I would rather not spend several hundred (2-5 hundred) extra for the added 5ah at this point in time. The fact of the matter is that I can resolve the bulk of my added range needs by taking the lesser cost route...primarily because they are actually not needs, just added conveniences and pleasures. For instance, an adjacent beach town (Rehoboth Beach, De.) has a mile long boardwalk that I'd like venture onto occasionally, along with my best buddy and scooter dog, "Junior". I adopted him about four years ago and let him keep the same name because it was the only thing from his past that he could bring with him from his former life in New Jersey. He loves to ride and I love to take him with me for some adventure, so it opens up our options quite a bit.....

By the way....you wouldn't happen to be a professor by vocation, would you? Your presentations have remarkable structure and clarity and that kind of ability doesn't come from changing tires for a living. In any case, I again thank you for enlightening me considerably. I hope with what remaining time that I have left that I may also gain the good fortune if visiting Sydney someday. I foolishly missed an opportunity to visit there for an R&R when I was on active duty in Vietnam and I've regretted it ever since.

I'll drop a note if I end up purchasing the 15ah LifePo4 from ebay......hasta la vista

 

[dogman dan]

FWIW, a reputable vendor of lifepo4 batteries for bikes and scooters is pingbattery.com.

A 10 ah size of pings cells is adequate to run a 20 amps controller, but 15 ah mo bettah.

You can guesstimate your average amps by the charger time too. Once you have a guess how many ah, then you use the run time to use that much ah for the next calculation.

Subtract about 10-15% from what the charger took, to get a more accurate guess how many ah you used.

 

[Windmaker]

FWIW, a reputable vendor of lifepo4 batteries for bikes and scooters is pingbattery.com.

A 10 ah size of pings cells is adequate to run a 20 amps controller, but 15 ah mo bettah.

You can guesstimate your average amps by the charger time too. Once you have a guess how many ah, then you use the run time to use that much ah for the next calculation.

Subtract about 10-15% from what the charger took, to get a more accurate guess how many ah you used.

Hey Dogman......thanks so much for the input. I think I would most likely go the 15ah route to be on the safer side, but I'm more concerned about the issue of buying from ebay sellers as well. Because of that hesitancy I just yesterday I passed on a sale of a 15ah that closed at $182. I've even seen some completed sales on the same battery at $150 level, another one at $119, and a few more under $200. Over four dozen units of that same battery pack have sold on ebay in the last three months ranging in price up to $315 and the sellers have over a 99% feedback rating. Of course that doesn't tell you much about how long those particular batteries will last, just that they probably work satisfactorily upon installation just after the sale time. Ping batteries on the other hand is selling their LifePo4 15ah at $533.....that's up to a $400 added cost. Do you think the ebay batteries (undoubtedly Chinese made) are necessarily that much lower in quality or reliability (or visa versa for the Pings), or do you just not know for certain.?

 

[999zip999]

I would buy from well know vendor that has support. Get a all in one plug and play battery system. So what amp controller do you have or what scooter ? If you get a under powered it will not last long.

 

[Windmaker]

I would buy from well know vendor that has support. Get a all in one plug and play battery system. So what amp controller do you have or what scooter ? If you get a under powered it will not last long.

I have a three wheeled 15mph mobility scooter from China that has a 48v system and uses 4 x 12v 20ah SLA batteries, and I suspect it uses a 20 amp controller. Do I understand you to be saying that a 20amp controller will accelerate the deterioration of a 15ah LifePo4 battery?

I'm also not so sure I understand your recommendation to get an all in one plug and play battery system.....what other kind is there?

I'll post a picture of the battery and charger I was considering bidding on

 

[dogman dan]

Just don't buy a dog turd from V power hong kong. They are a long time vendor of shit quality packs. Primarily just shoddy assembly is the problem.

Most pingbatteries have lasted 3-4 years, a few longer. But hey, if you only have $200, then there you are. Just don't gamble with money you can't afford to lose.

 

[Windmaker]

Just don't buy a dog turd from V power hong kong. They are a long time vendor of shit quality packs. Primarily just shoddy assembly is the problem.

Most pingbatteries have lasted 3-4 years, a few longer. But hey, if you only have $200, then there you are. Just don't gamble with money you can't afford to lose.

Yes, I've seen the V power packs, so now I know to scratch them off the list for sure. Thanks Dan. The other packs that I referred to are selling at up to $350 or more, but I still have some doubt about them also, so I'm still not certain of my decision. You're right on target about my not gambling with money I can't afford to lose. I'm a retired vet on a very limited income, so I do have to be careful on my spending. Incidentally, I take it from your username/handle that you may have a canine buddy. Just wanted to let you know I have an 18.5 lb (big) Pomeranian who loves to ride with me...he's my chick magnet. :wink:

 

[999zip999]

Just give us a link before you buy. Lots of crap out there. Dogman gambled on a cheap pack didn't do so well.

 

[Windmaker]

Just give us a link before you buy. Lots of crap out there. Dogman gambled on a cheap pack didn't do so well.

Here's the battery I was watching (which has a history of sales from $119 to $315 at auction and asking prices elsewhere at $350 and up).

http://www.ebay.com/itm/381840096331?_trksid=p2060353.m1431.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

[dogman dan]

My gamble did Ok,, but right out of the box it delivered about 18 ah, instead of the rated 20. Now two years later still running, but delivering 16-17ah depending on how hard I pull on it.

That's typical for the cheapo packs, they just don't have such great cells in there, so they may be rated 2.5 ah per cell, and deliver 2.3 or whatever. So buy the 15 for sure if you go alibabba.

 

[Windmaker]

My gamble did Ok,, but right out of the box it delivered about 18 ah, instead of the rated 20. Now two years later still running, but delivering 16-17ah depending on how hard I pull on it.

That's typical for the cheapo packs, they just don't have such great cells in there, so they may be rated 2.5 ah per cell, and deliver 2.3 or whatever. So buy the 15 for sure if you go alibabba.

Thanks for the heads up Dan

 

[Windmaker]

My gamble did Ok,, but right out of the box it delivered about 18 ah, instead of the rated 20. Now two years later still running, but delivering 16-17ah depending on how hard I pull on it.

That's typical for the cheapo packs, they just don't have such great cells in there, so they may be rated 2.5 ah per cell, and deliver 2.3 or whatever. So buy the 15 for sure if you go alibabba.

Thanks Dan