36v 20ah vs 48v 10ah LifePo4 battery

[kmxtornado]

Albeit slow, I'm still learning so please bare with me for this newb question.

I currently have a 36v 10ah battery and am looking for an upgrade (yes, already). I was looking through the Tech and FAQ's section for some info and stumbled upon the power calculator. Since volt x amp = watts, the 36v 20ah battery puts out significantly more watts than a 48v 10ah battery. Is there any reason I would want to go from a 36v 10ah battery to a 48v 10ah battery if my 36v 20ah battery was my alternative? No, right (other than price since a 36v 20ah battery is lots more $$$$ than a 48v 10ah one)? I should see significantly more improvement in the 36v 20ah battery.

If not these two types of batteries, what would you recommend as an upgrade worth spending money on that's still a LiFePo4 battery? Perhaps a 36v 16ah battery? Please keep in mind that I have the Mini Might kit: https://hightekbikes.com/shop/index...oducts_id=10&zenid=36uk0batfffcv5e5e4ns088au4 which is 350w nominal and 500w peak. Does that mean that if I have any wattage over 500w, it would be a waste and unused since the motor's capped at that level? Not sure what that means exactly. Please help clarify.

My 2 year warranty is only good for a 36v battery so I'd like to stick with that voltage. I guess that's another reason to get a 36v battery. My current controller is the upgraded 20ah one.



Please share your thoughts and recommendations. Thanks!

 

[neptronix]

You're missing 1 part of the equation.. C rate.

And you don't need to talk about how many watts are going to come out of a battery when you're considering how much it can put out, you want to talk about amps.

If you have a 10AH battery that is rated for 1C, you can push 10A out of it ( 10AH x 1C = 10A )
Now the same 10AH battery, if it's 3C, then you can push 30A out of it. ( 10AH x 3C = 30A )

Does that make sense?

When selecting a battery, the first thing to consider is the amount of amps your controller will pull. ( find that out first ).
Secondary is how much range you need.

more amp hours = more range. But you may need to go overboard on the amp hours so that you can deliver the amount of amps needed.

This is generally no problem with RC lipo, that's why you see it get used a lot. One 5AH 20C pack can put out 100 amps.. 5AH is not a lot of capacity though, but it works

 

[amberwolf]

Since volt x amp = watts, the 36v 20ah battery puts out significantly more watts than a 48v 10ah battery.

Not really. Ah (amp-hours) is capacity; you're thinking of A (amps) which is current flow.

If you put a load on either battery, with the load being the same resistance, the 48V 10Ah battery will produce more instantaneous power (W, Watts) because the higher voltage will cause more current to flow thru the resistance of the load.

The 36V 20Ah battery will be able to sustain it's lower power level for longer because it has more Wh (Watt-hours), but the actual instantaneous power (W) will be lower because of it's lower voltage causing less current to flow thru the same resistance of that load.


The only exception to this is if the BMS in the 48V 10Ah battery is set to cut off power if greater than a certain amount of current flows, and that amount is notably less than the current that would be allowed by the BMS in the 36V 20Ah battery. That is unlikely but it might possibly be the case if these are low-C-rate packs.

Is there any reason I would want to go from a 36v 10ah battery to a 48v 10ah battery if my 36v 20ah battery was my alternative?

Yes, if you want either more speed or more power out of your motor system, assuming that your controller is designed to handle 48V+, or you are willing to replace it with one that is.

Also assuming that the BMS in the pack will allow sufficient current draw to support your systme at the higher power level, and that the C-rate of the pack is sufficient to survive such use over the length of time you wish to own the pack and use it.

To know what C-rate you need, you would need to use an amp-meter (or wattmeter that records peak and average amps, or displays it realtime and you have time on the road to watch it during various types of terrain and startups/etc). That will tell you how many battery amps your system is drawing from your existing pack, to know if it is limiting you at all. If it is constantly drawing near the peak your existing pack can provide, but nto as much as the controller is capable of drawing, a higher-C-rate pack might help in some cases. But if the amps you see are already at the controller limit, you would also need a higher amp-limit controller (assuming the motor could survive that).

No, right (other than price since a 36v 20ah battery is lots more $$$$ than a 48v 10ah one)? I should see significantly more improvement in the 36v 20ah battery.

Only in range (because it has more total Wh). Not in power.

If not these two types of batteries, what would you recommend as an upgrade worth spending money on that's still a LiFePo4 battery? Perhaps a 36v 16ah battery?

What do you want the upgrade to do? Provide more power at the wheel? Or give you more range?

The former would probably need a higher voltage, and the latter could use either higher capacity or higher voltage, because both will give you more Wh. If you do not use full throttle with a higher voltage pack (3/4 throttle with 48V vs full throttle with 36V, for instance) you won't use up the capacity any faster than if you did use full throttle with the lower voltage pack.

Please keep in mind that I have the Mini Might kit: https://hightekbikes.com/shop/index...oducts_id=10&zenid=36uk0batfffcv5e5e4ns088au4 which is 350w nominal and 500w peak. Does that mean that if I have any wattage over 500w, it would be a waste and unused since the motor's capped at that level? Not sure what that means exactly. Please help clarify.

No. 500W peak means that it is only designed (or at least "rated") to handle that much power at most. If it is a geared motor it could mean that the gears might not be designed to handle more than that, or more likely it means that it can't handle the heat generated by higher loading than that. Probably also means that continuous use at higher than 350W could overheat it. Some motors are rated much much lower than what they can actually sustain, but it depends on how much cooling they can get. I don't know what hte limits of the Mini-Might actually are.

On my "350W" Fusin geared motor, it gets awfully hot at higher loads, in the 1200W peak range, probably half that constant, enough to begin cutting out becuase (I think) the halls get so hot that they stop operating correctly, so the controller cant' commutate the motor. I know it's hot enough I couldn't leave my hand on the case for long, so the inside must be REALLY toasty.

That's one problem with geared hubs--they have two layers of thermal transfer to go thru before heat can escape the motor, so they often cant' be safely run on higher power for very long, especially if they are very smal motors. Heat must first go from the stator thru the airgap to the magnets and rotor bell and planetary/clutch, and then once those heat up enough they can radiate thru the air gap to the motor casing, and then after that heats up it can radiate to the outside air.

My current controller is the upgraded 20ah one.

Do you mean 20*A* controller? Just to be sure, A is a rating of current capability, and Ah is a rating of capacity.

 

[kmxtornado]

Thanks for the replies. Very technical, but I'm trying to absorb it all in.

Yes, I meant a 20A controller is what I have. My goal for the upgrade is for more power and speed. the 10ah battery I have now is great for the range. I've ridden 17miles and only one of the three "fuel" light indicators has ever flashed. I assume I have a lot more juice to go. So it's definitely not range that I'm trying to increase. That's perfect. It's the speed and torque that I'm looking for upgrades on.

But of course, I don't want to burn or break anything that I have existing. So with that in mind, is it the 48v 10ah battery that I should be getting? I have no idea what the c rate is for the 36v 10ah battery I got from HTB. Copied from their website, these are the specs of my current battery:

* 36V 10Ah LiFePO4 Rechargeable Battery Pack
* Integrated BMS with cell balancing function.
* Voltage : 38.4V(working) 43.2V(peak) 30.0V (cut-off)
* BMS cutoff current: 30 amps
* Recommended continuous discharge: 20 amps
(with estimated 85% capacity after 1200 cycles)
* Continuous discharge: 25 amps
(with estimated 80% capacity after 900 cycles)
* Maximum peak discharge: 30 amps (10 sec)
* Pack Configuration: 12S7P, Type 18650 cells.
* Max. Charging current: 4 amps

Perhaps one of you can help me interpret that. My question I guess is whether the 36v 20ah battery or the 48v 10ah battery would:
A. Benefit me at all?
B. Be harmful for my controller, motor?

Maybe my motor's already at its max and I'm trying to improve something that doesn't have much more room. Not sure. Terry did say though that the motor can run on a 48v battery but not for sustained lengths of time. I suppose that's why it voids the warranty. I can be disciplined if that's what going to take to get significant speed (5mph or more gains) that a 48v would require. But at the same time, I don't want to risk anything if there's possible damage that could happen to my setup. I would just rather wait 2 yrs 'til my warranty is over before messing with it further. Let me know your thoughts. Thanks.

 

[NeezyDeezy]

Just to be clear, going to 36V 20AH won't change anything unless you modify your controller, which you shouldn't do.

Stick with 36V 20amps on the minimight. It gets too hot at 48V 20amps if you ride for more than 5 minutes or up hills. I only ride mine in the winter here in Pittsburgh (average low of 19 degrees), but in the bay area you will melt those gears unless you stick to short trips. Do an experiment, at 36V, ride up some hills for a couple minutes, then feel the hub motor casing with your hand. Now imagine it being twice as bad with more current.

These motors are fantastic for stealth and weight. They're actually my favorite of any motor. Keeping the current low actually helps keep you safe and stealthy.

 

[kmxtornado]

Just to be clear, going to 36V 20AH won't change anything unless you modify your controller, which you shouldn't do.

Stick with 36V 20amps on the minimight. It gets too hot at 48V 20amps if you ride for more than 5 minutes or up hills. I only ride mine in the winter here in Pittsburgh (average low of 19 degrees), but in the bay area you will melt those gears unless you stick to short trips. Do an experiment, at 36V, ride up some hills for a couple minutes, then feel the hub motor casing with your hand. Now imagine it being twice as bad with more current.

These motors are fantastic for stealth and weight. They're actually my favorite of any motor. Keeping the current low actually helps keep you safe and stealthy.

I think you mistyped something above (I bolded it). Are you suggesting that I stick with what I have?.....the 36v 10ah? Looking forward to your response since you have first hand info with a Mini Might.

 

[NeezyDeezy]

I and a couple folks have tried to point out the difference between battery capacity (amp-hours or AH) and amps (current). Take a look at YPedal's faq here:

http://endless-sphere.com/forums/viewtopic.php?f=3&t=26488

let us know if you have any questions, we'll be happy to help -- even if I'm still learning too!

 

[kmxtornado]

Thanks, but can you please clarify your initial statement I was asking about in my post above? It sounds like you're suggesting to stick with the 36v 10ah b/c the 36v 20ah one will only give me a longer range which I'm not in need of. The 48v one would generate too much heat to be safe or healthy for the system. Is that correct? Please note, I was asking about the 48v 10ah battery - not the 48v 20ah battery (that I know would be overkill). You wrote 36v 20ah twice so I just want to be certain I'm interpreting your suggestion accurately.

 

[wesnewell]

A 20ah battery will give you very little more power, depending on sag of the 10ah pack, but it will not give you any more speed. Going from a 36v 10ah battery to a 48v 10ah battery will give you both more power and speed. 36v battery with 20A controller = 760W nominal. 48v battery with 20A controller =960W nominal. If you want more power and speed, your only choice is a higher voltage pack. I have no idea what your motor will handle, but if it should handle 960w for a minute or two. Of course you don't have to do that. You can limit the current by not going wot all the time.

 

[John in CR]

Just to simplify it for you. Going from 36V10ah to 36V20ah will double your range and little else other than extend the life of your battery pack because it's twin means only half the stress. The small increase in performance isn't worth considering with that small motor, and the rationale will only be confusing at your stage of the game.

Increasing the pack by 12V to 48V will increase speed, acceleration will be slightly higher and the pull of accelerating will last longer. You may or may not need a new controller, typically not when going from 36V to 48V. If your motor also comes with 48V kits, then the motor should handle it ok. Going to 48V10ah gives you more stored energy, now 480 watt-hours vs the 360wh before, but you typically don't see much, if any, range increase, because you'll eat up the extra juice with more performance.

You don't necessarily have to buy a new 48V battery to get where you want. You could just add a 12V10ah battery in series with the 36V with a big diode in line between the 2 to protect the BMS of each from voltage spikes that can occur when one of the batteries shuts down. It's a super simple thing to do, so not a worry if you're non-electrically inclined, and definitely worth the $300 or so that you'd save, maybe even take some of that savings and buy a better and/or higher capacity 12V pack such as on with A123's from Cellman. That way the 12V pack can be included in your upgrade path, since the search for more performance is endless.

John

 

[kmxtornado]

Okay, I'm clear now. You've validated a newb's suspensions are correct in thinking that 20ah vs 10ah only provides more range and not much else.

Adding 12v to the existing 36v battery, huh? Wow, that's definitely something to think about! Hmm.....That would certainly fit the bill and definitely be more worth it than forking over $350 for a 48v 10ah battery. The advantage of replacing the battery entirely though is that I can put that 36v 10ah battery permanently in my mini foldable scooter (see sig). If I can save $250-300 though, that would be the way to go for me.

You could just add a 12V10ah battery in series with the 36V with a big diode in line between the 2 to protect the BMS of each from voltage spikes that can occur when one of the batteries shuts down.

Wow, that's way over my head. Any place I can read up on what that means in laypersons terms? I trust that it's easy, but I wouldn't know where to start in terms of physically hooking something like that up. I'm a DIY with cars (changing brakes, replacing O2 sensors, replacing suspension components, etc), but when it comes to electricity I'm just scared and not very knowledgeable. Can you guide me further to the right direction? Any resources I should be reading up on? or do you have pics of something similar that you or someone else has done?

Thanks so much. Very helpful info.