Minimum Lifepo4 for a 750w motor?

[mst3kpimp]

I really want to make the leap to Lifepo4 but I'm confused about what I can use. I have a 750w brushless front hub Aotema I got from HTB with the standard 36v controller. I'm satisfied with with the speed so I'm not looking to go past 36v. I see at Pings website the only thing listed thats compatible with a 750w motor is a 20ah Lifepo4 which is just too pricey for me. Is this really the minimum I can use with my setup? What would happen If I ran a 10ah or 15ah pack? My terrain is flat, I weigh 220 and my trips are usually under 8 miles.

 

[dnmun]

from a financial point of view, buy the biggest pack you can carry on the bike. the cost/Wh is lowest that way.

since it is a long term investment, recognize that by the time this pack has expired, the new one will cost twice as much. so by getting a large capacity pack, it will last longer and therefore put off the time when you have to shell out the big bucks.

that is how you can conserve your cash best, imo.

so go with 48V20Ah and cut back on the beer budget. you will be replacing the motor and controller before the pack.

 

[dogman dan]

That motor and stock controller will run on 10 ah. No hills helps, and you'll have 8 mile range for sure. But the battery will be under considerable strain, often pulling 2c when leaving the stop sign. This will shorten it's lifespan for sure. But that doesn't mean it will fail in one season. It doesn't mean it couldn't fail in one season either. It's a matter of luck in a way. But in a pack tht small, each section is just two cells paralelled. So one weak cell and you are down 50%. In a 20 ah pack one weak cell and you are down 25%. So with the smaller packs, your luck of the draw that all the cells in the pack are perfect becomes more crucial. There will be more pull on any weak cells, and they will die fast in the small pack. So it's just a situation where the larger pack has you less dependent on each and every cell being really perfect.

15 ah is a good compromise. I have a 48v 15 ah that I have been running on similar wattage motors for almost two years now, and it's fine. I expect it to last at least as long as my first ping did, which was 700 cycles. It died only because I made a mistake in the end. Left it on a bike with the controller on for a month.

I would say go ahead and get the 36v 15 ah. You will have just about enough range to go about 16 miles, and charging every 12 miles or so would be best.

 

[gge5]

Ping batteries are rated for 2C continuous, 4C max.
2C from a 10Ah, 36V pack is 720 Watts. That's certainly pushing the boundaries.

Headway cells, however, are rated for 5C continuous, 10C max.
That would be 1,800 watts continuous from the same size pack.

If you buy Headway 10Ah screw terminal cells and the KP-J charger from EV Assemble (don't buy the BMSes, they're crap), it would come to about $300 with shipping to the US. I wouldn't be surprised if it took 2 months to get to your door though.
I'd get a Zephyr BMS to go with your pack.

 

[SamTexas]

I really want to make the leap to Lifepo4 but I'm confused about what I can use. I have a 750w brushless front hub Aotema I got from HTB with the standard 36v controller. I'm satisfied with with the speed so I'm not looking to go past 36v. I see at Pings website the only thing listed thats compatible with a 750w motor is a 20ah Lifepo4 which is just too pricey for me. Is this really the minimum I can use with my setup? What would happen If I ran a 10ah or 15ah pack? My terrain is flat, I weigh 220 and my trips are usually under 8 miles.

The motor and the controller do not necessarily determine the needed size of your battery. How you actually use your bike is the determinant factor. Therefore you need to measure your current usage: What is your current typical energy consumption? In wh/mi. What is your current average speed?

Example: Let's say your current average speed is 18mph and your current energy consumption is 15wh/mi. That means your average power consumption is 270W (18*15). A 10Ah, 36V Lifepo4 (2C continuous, 4C burst) can supply 720W (10x36x2) continuously. 720 is 2.67 times 270, so that 10Ah pack is more than sufficient for your bike and will provide you a range of 24 miles (360/15).

 

[el_walto]

I don't see any problem with using the 10AH ping battery pack with your 20amp controller. This should meet your range requirements also.

 

[Hillhater]

,....recognize that by the time this pack has expired, the new one will cost twice as much. so by getting a large capacity pack, it will last longer and therefore put off the time when you have to shell out the big bucks.

Cell costs, as with most new electrical tech, have shown a consistent fall over time.
Why do you expect that to change so dramatically in the future ?

 

[dogman dan]

Well, 2c lifepo4 cell prices have been pretty much stable for the last 4 years for one. Production prices falling may not ever lower retail price.

But the short answer is. Get the 15 ah ping. why, it costs 30% more!? Because the range you plan to ride your bike will at least double, if not triple, when you find out how nice it is to have range. In fact, if you are smart, you'll get the 36v 20 ah, or 48 15 ah. Having 20-25 miles of full throttle range is very nice, and 35 miles of slower range is beautiful.