Options for a small (6-10ah) 48v battery

Hey, had some issues with a road bike project so stepping back and reworking the setup.

I'm replacing the broken q128c with a 36v 260rpm 500w Bafang CST and potentially a S12s controller but currently have a 20a sine wave controller.

The main issue I had was the added weight of my battery, when speaking to the battery builder I didn't think I would be converting a light weight road bike so purchased a 48v 17.5aH shark style battery. I just weighed this and it came in at just over 4KG! Its been making the ride horrible and I flinch at every bump I hit.

What I have learnt though is that I don't need a large capacity battery, my commute is 6 miles and I can charge at work. The route is fairly flat but theres a few hills where I feather the throttle but I rarely go past 500w. It currently take around 16 miles for the battery metre on the battery / LCD3 to drop to 3 bars and that with hammering the throttle and PAS too.

So, after another thread on here it would seem a 6 / 8 / 10 ish aH battery would suit me fine. Before I jump into purchasing one however I would like to know my options...

It has to be 48v (maybe 52v) and needs to be able to take 25 - 30a continuous. I've the bottle type batteries but wan't to go a bit more stealthy. I've seen a thread where the person uses 10 batteries inline and puts them in the seat post and stills get 4ish aH.

Although I would love to build my own battery, i'm not sure i'm quite up to it! The options i'm looking at are:

- Getting the same battery seller to clone the mighty mini or create something that can fit in a seat bag.
- Looking at RC lipo's? This is a new one to me and they seem light and flexible in terms or adding more / less. My main question with them is how I go about knowing how many amps I can pull and also how I configure 48v / combine batterys together? Do you need any sort of BMS with them too?

Take Hobby King (although im UK based) for example: https://hobbyking.com/en_us/graphene-6000mah-4s-65c-w-xt90.html?___store=en_us

It talks about 'C''s 'S's and is only 14v. What is the logic / can anyone provide guides or threads on how people have combined these to make 48v setups?

I've heard of dangers with RC lipos too, maybe its worth me just taking a look into making something simple and small with 18650 pre welded batteries?

Sorry for the long post! I can't stand just buying stuff without understanding and thinking about how it all works!

Based on your post; I would suggest going with the safest route: going with your current battery supplier if you are happy with their work. Tell them your performance desires: V, Ah, and shape of the battery.

nfmisso said:

Based on your post; I would suggest going with the safest route: going with your current battery supplier if you are happy with their work. Tell them your performance desires: V, Ah, and shape of the battery.

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I agree, i've just messaged them asking if they can match the size and weight of the Mighty Mini so hopefully they can sort something out for me. I've looked at the DIY kits you can get with the connecting blocks etc but I just don't have the time!

- Looking at RC lipo's? This is a new one to me and they seem light and flexible in terms or adding more / less. My main question with them is how I go about knowing how many amps I can pull and also how I configure 48v / combine batterys together? Do you need any sort of BMS with them too?

Take Hobby King (although im UK based) for example: https://hobbyking.com/en_us/graphene-60 ... tore=en_us

It talks about 'C''s 'S's and is only 14v. What is the logic / can anyone provide guides or threads on how people have combined these to make 48v setups?

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There is reams of info on the Net on RC LiPoly, you only need to search and study. So, I will not spend time teaching you about it, but will respond only about the things about LiPoly that apply to YOU.
Yes, it is great for small packs and can be very modular.
Considering that you will have to spend money on a LiPoly specific charging set-up(more detail on this later), it is always best to try and buy LiPoly on sale.
In the past, the Multistar from HK has been a very popular LiPoly for ebikes. It was designed for quad copters and trades a low dis-charge rate for smaller size, lighter weight, lower volatility and lower price. And it has been on sale @ HK on a regular basis, but unfortunately, it has not been for quite some time.
At the moment, I only see two "bricks" that I think would be appliable to your needs on sale. They are;
1)
https://hobbyking.com/en_us/turnigy-battery-4000mah-6s-30c-lipo-pack-xt-60.html
I have always liked the regular Turnigy stuff and this is a great deal. You could use 4) for a 12S(45.6 V nom.)/8000mAh, 2S/2P(2 in series, 2 in parallel)pack. It would be a small 6lb. pack for $120 US. The 30C discharge rate is more than enough and for your proposed system, even the lowly Multistar 10C would be enough(The Graphenestuff you listed is way overkill and not a good use of your LiPoly money). You wouldn't get the whole 8 Ah out of it in the real World, maybe 7 AH, but LiPoly is very sag resistant and you would get close to nom. Voltage all the way down to end of dis-charge. 2 bricks in 2S would be a very small 4 Ah pack.
Another option would be;
https://hobbyking.com/en_us/zippy-compact-4500mah-6s-40c-lipo-pack-xt90.html
Same deal either 2S/1P or 2S/2P for 4500 mAh or 9000 mAh packs respective.
The 40C discharge rate is not needed(But doesn't hurt), but the little extra capacity would be nice. I've used Zippy over the years, but not the Compact. I've always thought the Zippy was ok, just not quite as good as the Turnigy(I'm talking about service life here and they both should be good for a couple of hundred cycles).
Although I prefer to bulk charge(charge the whole pack as one unit), because of the ease to remove and disconnect the bricks, you could use a 6S rc charger. I cut off the XT connector and replace them w/ Turnigy 6 mm bullet connectors and you would need some 14 AWG wire(again, Turnigy from HK)and some Y-adaptors(for the parallel connections), maybe $50 US.
These bricks are so small, I use a very tiny, "over the top tube" frame pack;
https://www.amazon.com/gp/product/B00P7OM6W4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
See GT link at bottom to see on bike.
I also make homemade tube/bottle batteries;
https://endless-sphere.com/forums/viewtopic.php?f=3&t=12847&p=938173&hilit=bottle+homemade#p938173
https://endless-sphere.com/forums/viewtopic.php?f=2&t=84624&p=1237928&hilit=bottle+stanley#p1237928
If LiPoly is something you want to persue, let me know and we can go into it in more detail.
.
Final note; Yes, there are ways to use 14S (49V)packs, but doing it gets more complicated. I would suggest 12S to start and trying 14S later when you have some LiPoly experience. For one thing, most controllers have a LVC(Low Voltage Cut-off) at 42V, which works well w/ 12S, but lets the cells in 14S get too low. You asked about a BMS, the LVC in the controller is the BMS.

motomech said:

LOTS OF AMAZING INFORMATION

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Thanks for your useful knowledge again! The RC Lipo's really interest me!

I'm ordering my motor tonight (Bafang 36v 500w) but also ordering a q100 along with it just incase I decide to do a light weight project in which RC lipo's would be perfect.

I've also messaged the battery company I know in regards to making a Mighty Mini clone in 52v so waiting on a price for that.

In the meantime, i'll be doing some research on combining batteries to get the 48v etc. If I can't figure out what I need from Google I'll be sure to message you.

Breifely though, is it essentially: purchase two of the 6s batteries and combine to make 12s but ensuring they charge equally?