1500w.. Minimum ah?

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Obsessed biker   10 µW

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1500w.. Minimum ah?

Post by Obsessed biker » May 29 2020 1:46am

Hi all, I'm new, but found and read a few threads here during my first ebike build. Anyway, I'm starting my 2nd build which is one of the voilamart 48v 1500w rear wheel kits with built in controller. The listing says it will need a minimum 14.5ah battery. But I thought the ah only indicated power over time and is considered when you're figuring range. I thought as long as you have the correct volts then the ah could be as low as even 5 or 8 ah. It just wouldn't last as long. I'm on a budget, but all the 14.5ah batteries I could find seem to be in a higher price bracket than even ones that are 13ah. My question is, do I absolutely have to have 14.5 ah for this kit to work? What about if I got a 52v that was only 13ah? Would the higher voltage make up some for the lower ah?

Sorry if this has been discussed before. I found a few threads talking about these kits, but couldn't find answers to this dilemma. Also, wasn't sure if I should've post this in the Battery Technology section. Administrators or moderators, please move this post to that section if you feel it's more appropriate there. 😀

On a side note, I'd appreciate any thoughts, tips or ideas regarding these particular kits. Mainly because they use an internal controller and another thread I saw talking about them was about problems with it. Fortunately, I didn't find a lot of threads about problems with them and these models seem to be popular. So if you've got one I'd love to hear what you think.

Thanks folks! I'm excited to be here!

Balmorhea   10 kW

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Re: 1500w.. Minimum ah?

Post by Balmorhea » May 29 2020 4:48am

To get 1500W peak motor output from a 48V electrical supply, you'll need 40ish amps. The problem with a typical small battery is that the cells, and/or the BMS, won't support a 40A discharge. There are exceptions.

The first blank you need to fill in, is how many maximum amps will your controller transmit from battery to motor? Might be 35A, might be 40A, or it could be something entirely different. I would not discount the willingness of Chinese sellers to call a hub "1500W" while furnishing it with a built-in 750W/20A controller.

Once you know the maximum current your controller will move, then you know the minimum current your battery should be capable of. More is better, in this case, because driving the battery to its limits is hard on it. Better that the controller doesn't approach the limits of the battery.

If you really want a battery you can run completely empty in ten minutes at full power, you'll need either a lithium polymer pouch cell battery like those used for radio control models, or a lithium titanate battery, or an unusually high rate lithium ferrophosphate battery.

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MadRhino   100 GW

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Re: 1500w.. Minimum ah?

Post by MadRhino » May 29 2020 9:04am

This is about battery c rate. High C-rate batteries can discharge high Amps even when they are low capacity. For a battery that has a discharge c rate of 1, it does have to be 40 A/h capacity to supply 40 A discharge. If its c rate is 10, then it could be only 4 A/h capacity and supply 40 A.

Then, you need some margin, because the battery c rate is quickly exceeded as its capacity is gone in discharge. The 1 c rate battery that was safely supplying 40 A when it was fully charged to 40 A/h capacity, is only safe to supply 20 A when it is discharged to half its capacity.
Make it fool-proof, and I will make a better fool.
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AHicks   1 kW

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Re: 1500w.. Minimum ah?

Post by AHicks » May 29 2020 9:47am

A lot of what you need for a battery is going to be about how you plan on riding this bike. If it's something where you aren't really needing or planning on using all of the motor's capacity, smaller batteries will work fine.

From a newbie standpoint, I would stick with a 48v batt. Reason being is some display will struggle with higher voltage, providing screwed up battery meter readings, as well as incorrect low battery voltage cut off points. It's an unnecessary mess.

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MadRhino   100 GW

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Re: 1500w.. Minimum ah?

Post by MadRhino » May 29 2020 12:07pm

Higher voltage will make faster speed, and will not change Amp unless it is set lower in the controller program. So you would have more speed and more power, because 40 A at 52 v does make more watts. If the controller is programmable, you could set lower Amps and limit the current, what you could do from the start with the 48v battery if you worry about its c rate, or the BMS does trip because you are pulling too much power.

If 48v does make a top speed that you are happy with and 40 A does make the power that you like, your best solution is a bigger battery, or a better battery. Then, there is range, that you don’t say about. There relies your ideal solution. A bigger battery will give you more range, while a higher c rate battery can give you more power but shorter range.
Make it fool-proof, and I will make a better fool.
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dogman dan   100 GW

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Re: 1500w.. Minimum ah?

Post by dogman dan » May 30 2020 7:00am

To simplify a lot. Get the battery way too small and you just murder it. Or as I like to say, you are beating that battery to dogshit.

15 ah, with todays better cells, will be fine. But with shitty no name cheap battery from ali express cells, you'd need double that. And be damn careful where you charge it. mine burned the house.

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Re: 1500w.. Minimum ah?

Post by 999zip999 » May 30 2020 4:36pm

You saved money on the wheel kit now spend it on the quality name and model number of cell. Also ask first as most poeple make the battery misstake.

Obsessed biker   10 µW

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Re: 1500w.. Minimum ah?

Post by Obsessed biker » May 31 2020 12:11pm

Balmorhea wrote:
May 29 2020 4:48am
To get 1500W peak motor output from a 48V electrical supply, you'll need 40ish amps. The problem with a typical ...

My first build, I got a good 52v 20ah battery with a 40a continuous bms.  I was really hoping not to spend as much this time and prefer not to steal it from my first build.  It would make sense though cause that one is a 48v 1000w front wheel and could run on a less powerful battery.

As for the maximum controller amps, I didn't see those specs anywhere.  However I checked the listing again and saw that 14.5ah was a recommendation, not a requirement.  So maybe 52v 13ah will do?

I thought about the lithium polymer option, but can't find the ones available with the voltage and capacity I've seen folks in vids used.  Where are they?  I checked hobby king already.

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Re: 1500w.. Minimum ah?

Post by Obsessed biker » May 31 2020 12:14pm

MadRhino wrote:
May 29 2020 12:07pm
Higher voltage will make faster speed, and will not change Amp unless it is set lower in the controller program. So ...

Where do I find info about the battery's c rate?  I've been looking primarily at the bms capabilities continuous and max discharge.

This kit has an sw900 display, so there is some adjustability with the output wattage.  I've only done just over 50mi on my first build which does 30 on the flats with a 52v 20ah, 40a bms and went the first 30 mi on one charge.  I'm happy with that and was hoping to get at least the same performance, but would sacrifice some mileage if it'd save $100-$200.

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Re: 1500w.. Minimum ah?

Post by Obsessed biker » May 31 2020 12:49pm

AHicks wrote:
May 29 2020 9:47am
A lot of what you need for a battery is going to be about how you plan on riding this bike. If it's ...
Well I'd hate to feel like it's a 250 or 500w motor (not that there's anything wrong with that), but being 1500w was a big reason I bought it. I'd be willing to sacrifice some range, but I've only got my first build as a basis for comparison. I figure I should have at least the same torque and top end speed, but maybe without over volting. Unfortunately, I don't know the specifics of the effects of all the different battery specs on performance of motors of varying specs.

I can see why you suggest 48v. Although my first build doesn't have a display, it has led lights on the thumb throttle, which has been far from accurate since I'm running 52v. A throttle with the voltage display will be the fix for that.

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Re: 1500w.. Minimum ah?

Post by Obsessed biker » May 31 2020 12:53pm

dogman dan wrote:
May 30 2020 7:00am
...mine burned the house...
That's crazy about your house. A beater battery may be a good option, and something I could use to test other builds. But how low of ah could I go and still be able to run 48v kits? I've had good results with my first and overvolting it to 52v.

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Re: 1500w.. Minimum ah?

Post by Obsessed biker » May 31 2020 12:55pm

999zip999 wrote:
May 30 2020 4:36pm
You saved money on the wheel kit now spend it on the quality name and model number of cell. Also ask first as most poeple make the battery misstake.
I had the same thought about my first build, so I got the 52v 20ah upp battery. Not the highest end, but decent batteries from what I read. Not to beat on a topic that I'm sure has been covered here, but what do you recommend?

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Re: 1500w.. Minimum ah?

Post by 999zip999 » May 31 2020 3:12pm

Which one as they make pack without a balance circuit in it's BMS be carefull and they sell models with generic cells and they sell packs if you paid more with high-quality cells which would be better.
Make sure you get a BMS that has a balance circuit in it yes to balance the battery
I recommend em3ev or ebikes.ca
I'm taking a chance with a custom battery by
Bicycle motor works. 72v20ah triangle pack.
Reread not a fan of internal controllers.

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Re: 1500w.. Minimum ah?

Post by donn » May 31 2020 3:37pm

Obsessed biker wrote:
May 31 2020 12:14pm
Where do I find info about the battery's c rate?  I've been looking primarily at the bms capabilities continuous and max discharge.
Max discharge will do. What you're buying is of course a pack of batteries. If the actual batteries in the pack are identified by manufacturer and model, then you can look that up and find out more, but the max discharge is derived from these parameters. Ideally, a peak maximum and a continuous or sustained maximum. You know how these values relate, right? A x V = W. So 1500W / 48V = 31.25 Amps. (None of these numbers are real, it's the principle that counts.)

Note also that your controller may have significant limits to how much current it will deliver.
Obsessed biker wrote:
May 31 2020 12:11pm
I thought about the lithium polymer option
Obsessed biker wrote:
May 31 2020 12:53pm
That's crazy about your house.
Forget lithium polymer.

Check the controller. If it's really a 1500W wheel, then I guess we have to assume it puts out at least 30A. In that case, you can get there with a battery that can handle a sustained 32A output or 30A at 52V, though a higher limit would be better.

My LiFePO4 battery advertises 50A continuous, 12Ah.

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Re: 1500w.. Minimum ah?

Post by Balmorhea » May 31 2020 3:44pm

donn wrote:
May 31 2020 3:37pm
Check the controller. If it's really a 1500W wheel, then I guess we have to assume it puts out at least 30A. In that case, you can get there with a battery that can handle a sustained 32A output or 30A at 52V, though a higher limit would be better.
That’s input power. Most motors are rated by nominal output power, which is why they use more electrical watts than their rating would imply.

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Re: 1500w.. Minimum ah?

Post by 999zip999 » May 31 2020 5:58pm

Email or call earlier Monday morning an make sure you have a balanceing BMS in the pack then ask what cells are inside like Samsung 30q or Panasonic ga or find out and ask us first for best cell opioon. Most important.
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Re: 1500w.. Minimum ah?

Post by donn » May 31 2020 6:31pm

Balmorhea wrote:
May 31 2020 3:44pm
donn wrote:
May 31 2020 3:37pm
Check the controller. If it's really a 1500W wheel, then I guess we have to assume it puts out at least 30A. In that case, you can get there with a battery that can handle a sustained 32A output or 30A at 52V, though a higher limit would be better.
That’s input power. Most motors are rated by nominal output power, which is why they use more electrical watts than their rating would imply.
Rather than "a 1500W wheel" I probably should have said "1500W controller" - the controller is in the wheel in this case, and the controller should be what practically determines the W rating, no? The motors are often the same regardless, I hear, and I think it's somewhat less than ideal to have the system be constrained by the battery's max discharge. The battery numbers are nominal, not real - voltage could be higher or lower (and real amp-hours is likely to be lower) - so this is just a hand waving approximation.

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MadRhino   100 GW

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Re: 1500w.. Minimum ah?

Post by MadRhino » Jun 01 2020 6:42pm

The seller did recommend a bigger battery, because he knows your choice of wheel (size and power) does require it to run good. Don’t try cutting/saving on battery size unless you buy it made with better cells and know for sure they will supply the current required.
Make it fool-proof, and I will make a better fool.
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Trek Session 10 mod. Variable geometry. 70mph
Dirt:
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Re: 1500w.. Minimum ah?

Post by 999zip999 » Jun 01 2020 9:53pm

Great name brand cells of known model number. Please don't do do something because of do do.
I'm concerned that a lot of people have given you clear guidance that you just might do your own thing anyway Clue ? Do as you Do.

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Re: 1500w.. Minimum ah?

Post by momus3 » Jun 07 2020 7:51am

According to the specs, that 1500 watts is factory restricted down to 750 watts.

I'd be concerned about the controller being built into the wheel. Does that mean that if the controller goes South, the whole assembly has to be replaced? That would be a deal killer for me. The unit construction means that if for any reason you wanted to change to another type of controller, it's not gonna happen.

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Re: 1500w.. Minimum ah?

Post by amberwolf » Jun 07 2020 4:09pm

This type of system usually requires either replacing with original controller, or running the phase and hall wires out thru the axle (or other) wire exit and using an external controller (this has been done with most of these systems at one point or another).

Generally not difficult for a DIYer, but it is some work and requires opening up the motor casing.

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