couple of battery pack questions.

Batteries, Chargers, and Battery Management Systems.
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couple of battery pack questions.

Post by Kenny'sID » Jan 15, 2017 10:35 pm

Is the full battery pack voltage calculated using the 18650 fully charged 4.22v or the 3.7v value?

What is roughly the maximum voltage a 1000w/48v hub motor can handle? Can't seem to find how many nominal 2100mah, 18650's I'll need for an 18ah/48v pack so hopefully those numbers will give me what I need to try to figure it out.

thanks. :)
Last edited by Alan B on Oct 11, 2017 9:52 am, edited 1 time in total.
Reason: fixed title typo

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Re: couble of battery pack questions.

Post by Voltron » Jan 15, 2017 10:56 pm

It's based on the nominal voltage...And the motor will usually handle any voltage... It's the controller that is voltage sensitive.
You're prob looking at 14 in series and maybe 8 or 9 parallel.

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Re: couble of battery pack questions.

Post by e-beach » Jan 15, 2017 11:41 pm

Kenny'sID wrote:Is the full battery pack voltage calculated using the 18650 fully charged 4.22v or the 3.7v value?
As stated above ..... 3.7v. But you can charge them to 4.2v multiplied what-ever you have in series and be fine. Although it is now known that if you undercharge your batteries they last longer.
Kenny'sID wrote:What is roughly the maximum voltage a 1000w/48v hub motor can handle?
That is open to a very large debate. Motors can be over volted until they melt. No one really knows what their hub motor can take until they push it. Do you have the budget to buy the controllers and batteries to push your motor until it melts? :lol:

What are the manufactures specs on your motor?
Kenny'sID wrote:Can't seem to find how many nominal 2100mah, 18650's I'll need for an 18ah/48v pack so hopefully those numbers will give me what I need to try to figure it out.
What are the actual cells you are going to use? Who is the manufacture and what specs are they?

18 cells / 2.1ah = 8.57 so you will need 8 or 9 per series to get 18ah.
3.7v / 48 = 12.97 so you will need 13 or 14 in series.

It also depends on your controller. If you really want to know what your controller can take, open it up and look at the ratings of the caps and the mosfets.

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Re: couble of battery pack questions.

Post by Samd » Jan 16, 2017 12:04 am

Its not the max voltage that matters, its the max voltage you need to run to stay in the 80 percent or better efficiency band.


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Re: couble of battery pack questions.

Post by Kenny'sID » Jan 16, 2017 12:31 am

Thanks all for the fast reply....very helpful.

OK, lets just assume I don't want to melt the motor, lol. But seriously, just a rough estimate would be helpful for the max V on the motor with all you all mentioned considered. These are all new/tested laptop batteries, BTW.

For the sake of simplicity, I'm considering a small pack designed to make it possible to remove the batteries and charge them in a stand alone charger every so often for balance. I'll be going with the plastic/4X battery holders like these... http://www.ebay.com/itm/5pcs-Black-4-x- ... Sw8gVX9gqP

I guess the advantages and disadvantages to that are obvious to all of you, but I doubt I know them all so any comments/advice on that would be helpful. Main reasons for me, it's a newb build and it does away with welding and trying to figure all the electrons out that would be eliminated this way, plus I'd just like to try something different, and maybe add a second one in the future for more capacity. I already have a couple of chargers that will handle 4 each, so charging separately won't be too tedious.

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Re: couble of battery pack questions.

Post by Kenny'sID » Jan 16, 2017 12:48 am

Oh, and a couple of you gave some good explanations on figuring the total number of batteries...if I could get the actual total, I could go back and better understand your calculations.

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Re: couble of battery pack questions.

Post by e-beach » Jan 16, 2017 1:16 am

48v at 18ah of 3.7v - 2.1 amp cells is something like 104 cells minimum. Consider purchasing a pre-made pack. Or do a bunch of more homework because trying to charge 104 or more cells in a little charger setup takes time. Not to mention a battery setup that can accommodate the removal, charge and reassembly of 104+ cells on a daily basis.

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Re: couble of battery pack questions.

Post by Kenny'sID » Jan 16, 2017 2:53 am

Thanks, EB, very helpful.

I won't be using it that often, so charging isn't really a problem, especially because, at least as I understand it, they don't really need balancing but every 5 to 10 recharges, but over 100 cells...I had no idea it would be that many. I was hoping to do small packs...part of my reasoning for this, but with that in mind, I'd have to do 2 @ 24v each, and just to give me minimum ah's for the bike, so, IDK...have to give it some more thought. That is unless I got some bad info when I read I need a minimum of an 18ah pack for the 1000/48v? If I can go smaller, I don't mind as I can add to it later, but again, not sure I can do that.

I'll need a few more batteries now than I thought/have, so plenty of time for research, and deciding how to go with this.

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Re: couble of battery pack questions.

Post by dogman dan » Jan 16, 2017 7:34 am

Nominal voltage, as explained above, is 3.7v. Most in the bike industry have settled into the standard for 48v being 13, 3.7v cells in series. This charges to 54.6v.

Others prefer a bit more speed, a tad more wattage, and run 14s. This charges to about 58.8v,, or some will undercharge a 14s, and go to somewhere around 57-58v.

Most 48v controllers have an absolute max rating of the capacitors inside of 63v. Open your controller, see 63v on the little cans inside,, there you are,, your max is 63v. Of course,, some push that some,, after all, your battery will sag a few volts as soon as you apply throttle. So with some risk, folks are known to run 15s,, or even 16s, especially if they also undercharge a tad.

And by the way,, if you are looking at power tool batteries, like mowers and trimmers, ,, they tend to go by 4.2v,, and call a battery 50v,, instead of 44v.

As for your motor itself,, its a 28 mm wide magnet direct drive. I've briefly run those at 4000w,, 40amps controller and 96v nominal. At 3000w,, usually a 72v 40 amps controller, you can run out about 10 ah worth of battery before the motor starts to damage itself. About an 8-10 mile ride full speed of 40mph.

A better, longer lasting plan for those motors is not to try to get 45 mph out of them. Let your full speed be around 30 mph or so, and run 48v 40 amps controllers. At 2000w it will ride very perky, and only risk overheat if you seriously overload one and ride up hills.

If you want 3000 or more, then you really must go to a much wider motor, with a lot more copper and wider magnets. then go for 5000w.

Now,, as for your battery plan,, bleah,, those holders I mean.

Assuming your current controller is 22 or 25 amps,, you need enough cells in parallel to put out 25 amps continuously.

A good rule of thumb for that is take the cells max amps rating, and cut it in half. So say one cell says it can do 4 amps,, calculate at 2 amps,, 25 amps will require about 13 cells in parallel. But you wont pull 25 amps continuous with that controller,, so figure on about 18 amps to cruise full speed, at 25 mph or so. For this example,, 18 divided by 2 amps,, you need 9 cells in parallel. Your cells might be better, or worse,, but at least 100 cells sounds about right.

That's the minimum,, if the cells are not real great,, 20 ah is a bare minimum. 30 would be my suggestion, unless they are top of the line cells.

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Re: couble of battery pack questions.

Post by Wheazel » Jan 16, 2017 7:43 am

How much capacity you need is not set in stone.
What are you going to use the battery for?

First and foremost: 3,7V is considered the nominal voltage of a common 18650cell.
The cells are in most ebike applications used between 3,0ish volts up to 4,1V or 4,2V.
4,2V is the voltage that is considered fully charged for all but a few exceptions.
The voltage will tell you how many cells you need in series, and what voltage you need to charge them.

There are two main reasons for more parallel strings.
One is to keep the discharge currents down for the single cell. (Depending a lot on what cell is used, and what discharge characteristics it has)
Example: If you have a 50V pack, and want to draw 20A ( for ~1000W), the battery will need to be in the 13-14s range and deliver 20A. If the cells are 2500mAh(2,5Ah) and happen to work best at 1C discharge or lower(for easy calcs), you could get 8parallel strings. Effectively making a peak discharge of 1C. 20/8=2,5

Two is to increase the size of the energy reserve to get more range. (Goes hand in hand with point one.)
Example: You realize that the energy from the 14s8p pack isn't enough to travel the distance you need, you can get any number of parallel strings to increase the capacity.
Be it 10p, 15p or 100p.

Riding an electric bicycle can require everything from a few Wh/km and up. Most bikes fall into the 10-25Wh/km territory.
For perspective, most cars run around 200Wh/km.
If you are going for a system that pulls 1000W, that will put a certain requirement on the battery.
But it can also be a 1000W "continuous" system that will pull much more momentarily, demanding more of the battery.

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Re: couble of battery pack questions.

Post by Kenny'sID » Jan 16, 2017 7:16 pm

Just a quick post to say thanks so much for taking the time, y'all..that's some fantastic info, answers a lot of questions, and then some. I'll be back once I absorb enough of it to comment. :)

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Re: couble of battery pack questions.

Post by Kenny'sID » Jan 17, 2017 11:11 am

dogman dan wrote:Nominal voltage, as explained above, is 3.7v. Most in the bike industry have settled into the standard for 48v being 13, 3.7v cells in series. This charges to 54.6v.

Others prefer a bit more speed, a tad more wattage, and run 14s. This charges to about 58.8v,, or some will undercharge a 14s, and go to somewhere around 57-58v.

Most 48v controllers have an absolute max rating of the capacitors inside of 63v. Open your controller, see 63v on the little cans inside,, there you are,, your max is 63v. Of course,, some push that some,, after all, your battery will sag a few volts as soon as you apply throttle. So with some risk, folks are known to run 15s,, or even 16s, especially if they also undercharge a tad.

And by the way,, if you are looking at power tool batteries, like mowers and trimmers, ,, they tend to go by 4.2v,, and call a battery 50v,, instead of 44v.

As for your motor itself,, its a 28 mm wide magnet direct drive. I've briefly run those at 4000w,, 40amps controller and 96v nominal. At 3000w,, usually a 72v 40 amps controller, you can run out about 10 ah worth of battery before the motor starts to damage itself. About an 8-10 mile ride full speed of 40mph.

A better, longer lasting plan for those motors is not to try to get 45 mph out of them. Let your full speed be around 30 mph or so, and run 48v 40 amps controllers. At 2000w it will ride very perky, and only risk overheat if you seriously overload one and ride up hills.

If you want 3000 or more, then you really must go to a much wider motor, with a lot more copper and wider magnets. then go for 5000w.

Now,, as for your battery plan,, bleah,, those holders I mean.

Assuming your current controller is 22 or 25 amps,, you need enough cells in parallel to put out 25 amps continuously.

A good rule of thumb for that is take the cells max amps rating, and cut it in half. So say one cell says it can do 4 amps,, calculate at 2 amps,, 25 amps will require about 13 cells in parallel. But you wont pull 25 amps continuous with that controller,, so figure on about 18 amps to cruise full speed, at 25 mph or so. For this example,, 18 divided by 2 amps,, you need 9 cells in parallel. Your cells might be better, or worse,, but at least 100 cells sounds about right.

That's the minimum,, if the cells are not real great,, 20 ah is a bare minimum. 30 would be my suggestion, unless they are top of the line cells.
OK, now I understand a lot more about exactly what the bikes can take power wise, that it's not just cut and dry, and why. That helps a lot.

My confusion with the necessary AH's to run my systems came from seeing some vendors selling 15 AH batteries for the 1000w, and then there is the guy on youtube running a 9ah for his 1000w and getting about 20mi out of it. I was just about to the point of thinking I need to just build something small and try it and see for myself what happens but, the info on this thread seems pretty reliable.

So, as long as I could go fairly small, I'd probably try the removable battery route, but 100 batteries minimum, or even 50 per pack if I divided it, are just too many batteries to deal with that way.

Its just that I hear all kinds of things about balance systems maybe not doing their job, something going wrong in there and the user not being able to determine if there is even a problem with a fixed system like that. Does anyone here recommend a more conventional non balanced system? I mean not something like I had planned but a fixed system where everything could be checked manually... I'm sure some of you have seen the "Balancer or no balancer" videos...that's what I'm talking about.

As for the way I'll be riding the bike, I'm kind of old so, especially on the three wheeler, 20mph is fast enough, as I can see serious problems with possibly flipping that thing or something close with a muck up at higher speeds. In my Sidewinder two wheeler, about the same speed seems safe but I can seem myself getting comfortable with it and maybe wanting more speed, but not much more. I do have to say, when they both were running right on electric power, they were pleasure to ride so, cant wait to get the kinks worked out, and as I say, get mor comfortable with em'. I think I'm still a little afraid of them. Several motorcycles, but until now, haven't been on any bicycle for probably 50yrs or better. I was actually wondering if I'd remember how to ride, then I remembered the obvious. :)

As far as amperage, I can tell you, the three wheeler, will blow a 25 amp fuse with anything extreme, like accidentally leaving the emergency brake on, and 30 amp seems to be working well for it. That should render some clue about the amperage....I guess.

On some of the details you mentioned, Dan, that's what I'm looking for, what most people do. So unless I run into a another situation where I can get a lot more good batteries quickly for under a buck each, I'll keep up the tedious task of gathering about 25 more batteries and go with the 100 battery/20ah pack recommend. I knew there was a thing about total amps necessary but am more clear on that now, and why the larger packs are a must for me. Thanks for that and everything else there, Dan.

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Re: couble of battery pack questions.

Post by Kenny'sID » Jan 17, 2017 11:20 am

Wheazel wrote:How much capacity you need is not set in stone.
What are you going to use the battery for?

First and foremost: 3,7V is considered the nominal voltage of a common 18650cell.
The cells are in most ebike applications used between 3,0ish volts up to 4,1V or 4,2V.
4,2V is the voltage that is considered fully charged for all but a few exceptions.
The voltage will tell you how many cells you need in series, and what voltage you need to charge them.

There are two main reasons for more parallel strings.
One is to keep the discharge currents down for the single cell. (Depending a lot on what cell is used, and what discharge characteristics it has)
Example: If you have a 50V pack, and want to draw 20A ( for ~1000W), the battery will need to be in the 13-14s range and deliver 20A. If the cells are 2500mAh(2,5Ah) and happen to work best at 1C discharge or lower(for easy calcs), you could get 8parallel strings. Effectively making a peak discharge of 1C. 20/8=2,5

Two is to increase the size of the energy reserve to get more range. (Goes hand in hand with point one.)
Example: You realize that the energy from the 14s8p pack isn't enough to travel the distance you need, you can get any number of parallel strings to increase the capacity.
Be it 10p, 15p or 100p.

Riding an electric bicycle can require everything from a few Wh/km and up. Most bikes fall into the 10-25Wh/km territory.
For perspective, most cars run around 200Wh/km.
If you are going for a system that pulls 1000W, that will put a certain requirement on the battery.
But it can also be a 1000W "continuous" system that will pull much more momentarily, demanding more of the battery.
Thanks Wheazel, that's very helpful. Like your post, the people on this thread are very good at understanding what basics some of us don't understand and making it clear.

I did have questions on the why's to parallel/series configurations, and that helps a lot.

I meant to ask, speeds of 35mph were mentioned, and mine would only get 20 or slightly more, all depending on if the bike computers were set correctly...should I expect more speed from these 1000w systems, and I'm not getting it due to the SLA's or is that about what I should expect with any battery?

Also, with my situation needing a fail safe system, one possibility was doing away with the gas, and going with 2 hub motors/separate systems. I know that sounds like over kill but one you break down and can't pedal home a few times, it's something we think about. Anyway, if I did go with that and wanted to carry a small extra battery pack for emergency, would there be any harm to using a 9ah or so just to get home with? (5/10mi or so) if I took any proper precautions? Be awhile on that but something I need to look into eventually.

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Re: couble of battery pack questions.

Post by Voltron » Jan 17, 2017 10:58 pm

Re the speed.. it mostly depends on the number of turns of wire in the motor. It's not that the 1000w one will go a lot faster.... it more that you can pump more power thru it for longer without it melting, say for extended hill climbing, or for accelerating heavy loads. But on flat ground, they won't be much different, assuming the turns of wire are the same, and and the higher rating comes from things like an aluminum stator or cooling fins or something that lets it dissipate heat quicker.

Looking at it from the other direction, sometimes the motor is deliberately wound to spin slower. For example, on a trike, maybe you still want to run it on 48V, but you just plain don't need the thing to be able to go 35mph. So instead of restricting the power... more wire turns in the motor will make it spin slower for the same voltage. The same thing goes for motors for different size wheels.. if you put a motor meant for a large wheel in a 20", its top speed is going to be a lot lower as the small wheel needs more rpm to get the same speed as a large wheel.

Thus 2 so called 48v motors might get you the same speed... or they might not.
Where the overvolting comes in is when you already have a motor that spins too slow for you... then you can volt that thing up and get some more rpms. But if you are starting from scratch, then you can just order a motor that is wound right for the target speed you want to travel on at 48v, or whatever voltage you like to run.

Also.. the motor can't tell if its running on SLA's or lithium (minus voltage sag differences) so switching to lithium doesn't automatically give a giant speed boost.. a volt is a volt as far as the motor is concerned. It will help the acceleration from the lighter weight, but won't change the top speed much.

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Re: couble of battery pack questions.

Post by Kenny'sID » Feb 05, 2017 4:51 am

Thanks, Voltron, your explanation on the over-voltage could come in handy, and till now, wasn't quite sure how that worked.

I need to find another way to get batteries besides bidding on new LT batteries for scavenge. I'm getting good 18560's all for less than a dollar each, but this is taking me forever, lol. It just seems sensible to go with my SLA's until I get enough Li-ion's for a build.

Just got my 56 tooth sprocket and chain in so I can actually wind that 6hp out a little, instead of it getting barely past idle, if that, plus have the tork I need , then hopefully I can get my backup gas drive working right/dependably so I have enough nerve to get out there and try the SLA's again. Getting on the road will help with my being a little more patient with the battery build.

If I'm popping 25a fuses with any extra drag on the bike but doing fine with 30's, is that a good indication of what kind of amperage I'm drawing? Between this thread and other reading, I'm finally getting why I need such a large battery. Takes things awhile to sink in for me. :)

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Re: couble of battery pack questions.

Post by dogman dan » Feb 05, 2017 6:32 am

If you will be pulling 30 amps, likely you need a minimum of 20 ah size, for a pack using not the very best cells. Yes, the bike may run on less, but the point is each individual cell will not like it, resulting in earlier demise of the pack. Use voltage sag under load as a guide, If you start at 56v, and sag to 48v with the first turn of the throttle, add more ah.


Re balancing. One thing I really wish commercial bms equipped batteries had, is a diagnostic port. Possibly under security screws so the average joe can't get at it, but built in.

The port would have a plug you can use to check voltage of each parallel cell group individually, and also therefore, force balancing if the bms is not up to dealing with a larger degree out of balance. This would allow a bike shop tech to quickly determine the condition of a battery, and attempt a non invasive repair by balancing it.

Build your pack with such a plug. For a bms, you will have a set of wires that lead from each group to the bms,, with y connections, add a "balance plug" to the pack. Now you can use devices like a cellog 8 to check the cells individually, and see if the bms is working well or not.

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Re: couble of battery pack questions.

Post by Voltron » Feb 05, 2017 10:03 am

Hey Kenny, now you can help me.. Lol. Where did you get the 56 tooth? I've been having trouble finding more that a 55. What bolt pattern, how much etc would be great!

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Re: couble of battery pack questions.

Post by James Broadhurst » Feb 05, 2017 3:35 pm

Kenny'sID wrote:For the sake of simplicity, I'm considering a small pack designed to make it possible to remove the batteries and charge them in a stand alone charger every so often for balance. I'll be going with the plastic/4X battery holders like these... http://www.ebay.com/itm/5pcs-Black-4-x- ... Sw8gVX9gqP
I've built a prototype pack (10S5P) out of these, or similar as I'm in the U.K., ABS holders
http://www.ebay.com/itm/BLK-ABS-Storage ... _NbKDsWGsA
because I've found the wiring of the ones you intend to use, to be not robust enough and the springs holding the battery in are quite weak.
I laid my batteries across a ribbon so that you just pull the ribbon to extract the batteries out of the holder.

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Re: couble of battery pack questions.

Post by Kenny'sID » Feb 23, 2017 2:28 pm

Voltron wrote:Hey Kenny, now you can help me.. Lol. Where did you get the 56 tooth? I've been having trouble finding more that a 55. What bolt pattern, how much etc would be great!
Hi Voltron, sorry bout not getting back sooner, I just diod find the subscribe button. Got it on ebay, but there was only one so, I'd suggest you keep trying or settle for something close. Even then, all the ones in that tooth range seemed to be few and far in between, but they were a few. I just hope the 56T works out... I took a guess at what I needed.

Let me know how it works out if you use that or one close to 56T and luck to you finding one if you haven't already.

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Re: couble of battery pack questions.

Post by Kenny'sID » Feb 23, 2017 2:38 pm

James Broadhurst wrote:
Kenny'sID wrote:For the sake of simplicity, I'm considering a small pack designed to make it possible to remove the batteries and charge them in a stand alone charger every so often for balance. I'll be going with the plastic/4X battery holders like these... http://www.ebay.com/itm/5pcs-Black-4-x- ... Sw8gVX9gqP
I've built a prototype pack (10S5P) out of these, or similar as I'm in the U.K., ABS holders
http://www.ebay.com/itm/BLK-ABS-Storage ... _NbKDsWGsA
because I've found the wiring of the ones you intend to use, to be not robust enough and the springs holding the battery in are quite weak.
I laid my batteries across a ribbon so that you just pull the ribbon to extract the batteries out of the holder.
I was a bit concerned about what the wiring on those could take too, James. I'll consider what you say if I should decide to try that in the future. How did it work out? Good enough to do it again, or at least improve on it?

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Re: couble of battery pack questions.

Post by Kenny'sID » Feb 23, 2017 2:45 pm

Thanks, Dogman, lots of good info to consider. Still gathering batteries..I should have gotten 25 laptop packs recently but the seller copped out on most of them, so may or may not get enough to proceed shortly. Tedious task but at around 30cents per new battery in some cases, I guess it's worth it if one has the time to piddle their way to the 100 or so needed, and I do.

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Re: couble of battery pack questions.

Post by Kenny'sID » Oct 10, 2017 10:05 pm

I, decided on a 14s/10p pack...it'll fit nicely for both applications/bikes, and it's a little more than the 18AH which someone suggested here/elsewhere?

Question: Can someone please tell me how many AH the mentioned pack will be?

Also, I've now got better than 450 batteries and enough for one full pack with matching batteries, and though I'm tempted towards the high drain they are now selling on ebay in 36v packs, I guess I'll start with these since they are a bit cheaper, and I need to use them anyway. Question:

How many mAh can these vary 100/200? more? Or is that not really a concern if I do the lay them out in a row thing from low to high and keep grabbing one from each end till I have what I need?

Question: I'll be going with the honeycomb type battery holders so they'll run a bit cooler. Will all singles attach to the solid x2, X3 or 4X5 or whatever solids? I guess I should just ask if they are all the same product and play well together as far as fitting together or are there different brands and don't all work together? Or I could just cut off the excess so no big deal either way.


One more question: On the 36v ebay packs I just mentioned, there is no way to get those to work with a 48v system without tearing into them, nothing feasible anyway? right?

Thanks again.. :)

Oh, fuse wire, what do I need and best place to order online?

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Re: couble of battery pack questions.

Post by 999zip999 » Oct 11, 2017 12:01 am

You're good at 18 ah I like a set (s) of sense wires for a monitoring device like an RC or cheap Chinese 8s at one time. Just buy a proper battery for your needs wattage amperage needs with a BMS that has Blinky lights to let you understand when each cell or parallel of cells is charged. Blinky lights helpful balancing and give great understanding after set of sense wires will help you to monitor understand and.

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Re: couble of battery pack questions.

Post by 999zip999 » Oct 11, 2017 12:05 am

Go try a bike at the local bike store and where do you live as it makes a lot of difference with battery shipping ebikes and what's available. ?

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Re: couble of battery pack questions.

Post by wturber » Oct 11, 2017 2:49 am

Kenny'sID wrote:I, decided on a 14s/10p pack...it'll fit nicely for both applications/bikes, and it's a little more than the 18AH which someone suggested here/elsewhere?

Question: Can someone please tell me how many AH the mentioned pack will be?
It will be 10 * the Ah of one cell. The "10" comes from the number of cells in parallel (10P). So if your cells were 2100 mah (2.1amp/hours) , you would have a 21 amp/hour pack.
Kenny'sID wrote: How many mAh can these vary 100/200? more? Or is that not really a concern if I do the lay them out in a row thing from low to high and keep grabbing one from each end till I have what I need?
The standard is to use all identical cells. I have no idea what the reasonable work-arounds are if you don't do that. I'd think that not having well matched cells is generally considered a "bad thing." But others with more experience can probably give better real world, practical insight into that.
Kenny'sID wrote: One more question: On the 36v ebay packs I just mentioned, there is no way to get those to work with a 48v system without tearing into them, nothing feasible anyway? right?
The general advice here seems to be to tear the packs apart and rebuild them to suit. There are clear advantages to doing that. You can custom shape the battery pack for a better custom fit. You can customize the voltage and capacity. You can create very high voltages and amperage configurations.

But that's not what I did. I'm using a DC-DC boost converter - which is pretty non-standard. Bottom line is that it is working fine for me. I've been commuting 32 miles round trip through a hilly area with a 1000watt direct drive with no problems. I put about 540 miles on my bike in about a month. I use either five or seven packs wired in parallel. When I can stop working 12 hour days in a few weeks, I'll probably reconfigure into two groups of four packs in parallel. Five packs are enough to get me to work and back and then a few miles on one charge. But I've been using seven packs lately to put less strain on the batteries and to have more flexibility to take side trips and/or go faster on some days.

The boost converter hurts efficiency a bit - probably by 5-7%. I run mine set to a 54v output. Its real world power limit (delivered to the controller/motor) set this way is 1175watts (the battery draw peak is about 1250 watts). My 48v 13A controller pulls a maximum peak of 26A. When it pulls more than the converter can deliver, everything shuts down for about five seconds and then power self-restores. That's not good when accelerating through an intersection or beginning a hill climb. I resolved this problem by using my S-LCD3 display to limit the controller to 80% of its maximum output. I no longer get any shut downs from demanding too much power from the converter.

So the converter limits my max power by 20% and I'm losing about 5-7% of my battery capacity. But I like the modular nature of my system. If a pack misbehaves, I can just pull it out and test it (I can plug my 10s charger in and check the pack balance if I wire in a BMS bypass) and replace a pack if it isn't performing properly. On the road, I could just disconnect a failing pack and leave the others connected. As a newbie to ebikes, I've avoided the whole business of designing and welding or soldering packs together (weld or solder? Nickel strips or fuse wire? Make sure strips aren't just nickel plated. Solder or weld? Build a cheap battery welder? Holders or not? If holders, which ones? What about the BMS? It isn't rocket science, but it does take more time and effort than rigging up a wire loom for multiple pre-made packs and mounting a DC boost converter.

I think the DC boost converter is fine for a commuter ebike if the rider likes to pedal along a bit on hills and/or when accelerating from a stop. If you crave more performance, then you'll want more than the 20 amps and 1175 watts that the DC boost converter can deliver. I see there's a 50/30A converter that might deliver 1500 watts (more than my controller should pull). If that device is smaller, it might be better than the converter I'm using. But that converter will deliver about 4 amps more than my controller can handle. My bike will do over 30mph unassisted on the flats. It handles hills with up to about a 10% grade with only mild effort needed from the rider. I'm commuting 16 miles in about 45-50 minutes on the downhill run to work and in about 50 minutes to 55 minutes on the uphill run back home. I could probably go faster, but I've been tending toward conservative use of power.

BTW, perhaps the biggest negative with those 36 volt packs (from alarmhookup on ebay) is that they are based on 2150mah cells. You can get better energy density (size and weight) by using higher capacity cells or using LiPo packs in parallel. I'm intrigued by the 22.2v 10A LiPo packs. My main concern is the lower voltage (44.4v nominal vs. 48v nominal). I'd probably be inclined that direction before I'd build a battery pack myself. The 36v packs are economical, but do add a bit of weight if you want to go relatively long distance. The weight doesn't bother me a lot. After all, I could shed a lot of that weight by running four packs and recharging at work. But with a heavy hub motor, it can add up to be a fair amount of weight.
"Commuter - DC Booster"
Iron Horse 3.0 hardtail - 48V / 1000W / 470rpm generic Chinese DD Hub motor (ebay)
7 x 36v 4.3ah 10s 2P battery packs - Wangdd22 1500W 30A DC Boost Converter delivers 54v and about 1175 watts peak
53T/42T Sakae Road cranks - 30mph+ on flats
https://endless-sphere.com/forums/viewt ... =2&t=90369

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