without knowing how that particular alarm is powered is difficult to say if you can wire then on to a switch... if it can be wired from a single on/off switch then it can be wired so it automatically come on when th ebike is turn on , but it will still involve plugging and unplugging the balance leads from the battery if you wanted to remove the battery.   The type of bms to buy would depend on what battery chemistry and the number of cells you intend to go for as lipo and lifepo4 have different specs , hk do not sell bms boards so you will have to buy through ebay .. i will try and find some links for suitable bms if you think it will be helpful.

I'm not sure I would trust the built in voltage cut out even with the standard batteries.  I had a hobbyking low voltage alarm which would go off before the bike cut out when I was running 6s lipos.  Now using a 6S and 3S in series on the 24V oset 16 and it goes much better.  Could be too much on the 12.5 though.

http://www.ebay.co.uk/itm/24V-25-6V-60A-LiFePo4-Battery-BMS-LFP-PCM-SMT-System-8S-3-2V-eBike-Battery-8x-3V-/321048902720 this is a link for a lifepo4 8cell bms

 

http://www.ebay.co.uk/itm/BMS-for-24V-25-6V-8S-LiFePO4-Battery-Pack-50A-10A-limit-With-Balance-/161637237107?pt=LH_DefaultDomain_0&hash=item25a2548173

 

I can only find ones for lifepo4 at the moment ( these are the most common ) ...

 

here are some general links for bms suppliers:  but postage cost can be quite expensive

 

http://www.bestechpower.com/pcmbmspcbforli-ionli-polymerbatterypacks/  

 

https://bmsbattery.com/66-bmspcm

you could use a CA ( cycle analysis ) to turn the bike off at a pre-set voltage but these are quite expensive, but on a plus side it will also give you a lot of performance information and will allow you to pay around with different throttle responses and configurations. 

I'm not sure I would trust the built in voltage cut out even with the standard batteries.  I had a hobbyking low voltage alarm which would go off before the bike cut out when I was running 6s lipos.  Now using a 6S and 3S in series on the 24V oset 16 and it goes much better.  Could be too much on the 12.5 though.

Which hobbyking low voltage alarm you have?

Has anyone tried this type?:

 

Protected 18650 3.7V 6000mAh Li-ion Rechargeable Battery For Torch Flashlight

 

(Copied straight from Ebay, seller called "Ebestonline").

 

It´s a cylindrical, type "tesla-Panasonic" battery that cost approx £46 GBP if you buy 30-pcs that gives you

a chance to build a 37Volts/18Ah pack or £64 GBP for 40-pcs(39 pcs needed) for a 48 V/18 Ah pack.

 

They claim these specs:

 

Description:

 

* Suitable for laser pointer, flashlight torch and other electronic products.
* Batteries can be used in torches, high drain equipment and any other 18650 battery applications. 
* Built-in protection circuit to provide over current protection and over discharge protection
* Capacity: 6000 mAH 
* Voltage: 3.7V
* Chemistry: Li-ion
* Keep in a dry and cool place
* Insert battery in right direction
* Color: Black
* Size: 64*18mm

* No memory effect, recharge up to 1000 cycles

 

I don´t know alot more than this but it sure sounds swell if the protection is built in from start.

They seem to have the same casing as a normal torchbattery(fairly rigid and protective?).

Can anyone of you tell me if they would be used on our kind of e-bikes(Seems to work for Tesla Cars)?

I would doubt the 6000mah claim unless they are only pulling mA when they were tested.. but sony and panasonic do make the highest power density 18650's ( as long as they are genuine ) but this is more in the region of 3000mah each  ( the last time I looked )  you will need to know what the over current spec actually is as it may not be high enough for our purpose.. yes they used to use these in the tesla cars but around 8000 of them and the cars are run on a much higher voltage than the bikes so on paper not as much current is required.. there are e-bike batterys made up of 18650's but these tend to have quite a low max discharge current ie a max of around 30-40A and are normally used for e-bicycles.. off road e-bikes can require a lot more than this sort of current limit.. 

Thanks, as i suspected there was a catch.

 

On my neighbour´s Ebike,48V1000W there is a 48V20Ah battery made up from 104 Samsung Cells(13S4P= Approx 5000mAh/Pc)

-and he has blown the 30(or 40?) Amp meltfuse on steep uphills, and I suspect it has some safety-headroom or margin

so perhaps a maximum of 50 Amps would be possible without killing that pack.

 

 

So now, either they are better than the Samsung cells or do they just come from someone who "Badge-engineered" them in to 6000 mAh

the way EarthX did when they allagedly posted their 6 Ah packs as being 18 Ah previously?

If they are up to spec, it would be neat building a 54 Ah pack at £192  .

How to charge a 13S9P Pack is another thing..

 

From school i remember NiFe-cells and Lead-Acid usually specified as 60 Ah/20Hrs or 60Ah/10Hrs giving a hint on use-purpouse

and internal resistance(Potential for accident;-), perhaps something to ask for as many just sell stuff without full specifications.

-While others of us(=Me) just use stuff without proper knowlege...

The battery alarms I am using are this one.

https://www.hobbyking.com/hobbyking/store/__18588__HobbyKing_8482_Cell_Checker_with_Low_Voltage_Alarm_2S_8S_.html

Mine is an older model that is shrink wrapped rather than the plastic case.

They are OK, but a bit of a fiddle as they go on the balance plug, so have to be manually plugged and unplugged (they aren't disconnected when you switch the bike off).

They also make a loud test alarm when first plugged in.  On the plus side they monitor each cell individually, and give you an accurate voltage display and they are cheap.

I guess ideally you would want one for each battery but I just use one and assume they are all discharging fairly equally.

I use extension cables for the balance plug which makes plugging and unplugging and mounting them somewhere visible a lot easier.

https://www.hobbyking.com/hobbyking/store/__9739__JST_XH_Wire_Extension_6S_20cm_10pcs_bag_.html

 

I have a cycle analyst on my bicycle and have to say they are really good if you have the money and can find a good spot to mount it (fairly big).

looks like this you can specify cell chemistry for this bms suppler.. but I expect that any supplier will have this option if you contact them.

 

 http://www.aliexpress.com/item/24V-8S-li-ion-battery-BMS-with-Balance-function-and-Max-60A-continuous-discharge-current-for/1724240995.html 

tried to to test my bike and added normal 12v battery in series so total voltage was 36v.Lights turned on but back wheel does not spin. Is there anything I can do that I get it working? I want to get it working before ordering lipos. I attached picture of my Oset 12.5 24v motor controller.

 

 

If you just replaced you're 24v with 36v then is will either work or it wont. Some controllers have a hvc built in so higher voltages can not be used , I think this may be more on the 24v controllers than the higher voltage ones. I think some people have used 36 on a 24 with success so I think there may be different controller models used on the range of the 24v bikes.

Can I remove HVC,  modify it or change it? 

No I dont think it will be a option to remove the hvc as there will have to be a fair few other modifications that would have to be done to the controller .. ( the hvc will be there for a reason )  .. you could look for a after market 36v or 48v controller something like this http://kellycontroller.com/kds72100e100a24v-72v-mini-brushed-controller-p-761.html  or even sometihng like this may be ok to try if you want it in a hurry and cheap :-) http://www.ebay.co.uk/itm/36V-800W-Speed-Controller-Box-Electric-Bike-Scooter-Brushed-/251638297450?pt=LH_DefaultDomain_3&hash=item3a96cfb36a  ..   I have no idea on how this controller will perform but for the price it may be worth a punt.

8s of lifepo4 will be equivalent to 24v sla as regards the voltage , but will give you much better performance and it will work on your 24v controller .. there will be very little voltage say ( unlike sla ) so you will have a higher top end anyway and this will also mean that you will have more power.