Booster battery - more volts, more speed question

[UKebiker]

Hi there

I am new to this forum and still fairly new to ebiking - so please be gentle with my probably stupid questions! I have tried to research as much as possible before asking this question and I've tried follow all the various posts on these issue but have got a little lost……..

I have a 8fun kit that I fitted to my own donor bike bought from here http://www.8funbike.com/detail.asp/sku=8F28F36B. I use it daily for a 16mile round trip to work along the coast - its flat but often strong headwinds.

The battery,I know from other research, to be fairly weak with high internal resistance on the Panasonic cells meaning voltage sag is pretty bad when drawing anything much (and its only a 15a controller)

Long story short I want to increase the voltage and increase speed (dont need greater torque/amps particularly). Easiest way I understand would be to buy a new 48v battery and controller (KU123 from BMS battery seems a good option for this)

However, funds are very tight and I just can't afford that option. I also don’t really need the extra speed all the time -just for, say, 5 miles.

So, I thought I could get a booster battery and hook up in series - and this is where I got lost !

I don’t have the booster battery so I have choices -could be any chemistry, any voltage or ah. The idea is to keep cost to absolute minimum.

I understand that seriesing up batteries of different voltage tends to kill one of them quite quickly. If is the booster battery I can live with that - if it’s my main then I probably can't.

I could, perhaps, wire up a switch that, when closed meant just the 36v battery goes to the controller and when open connects booster and main battery together. So the booster battery is only getting current through it when I actually need it

I'd be most grateful for any help here. I'm not really after the perfect solution - just a workable one on a shoestring budget (if this is at all possible). I've got some bosch drill battery packs of 12 and 14.v volts but anything else would need to be purchased. Stll Nicads and Nimh for RC type applications seem freely and cheaply available.

Thanks very much indeed

Kirstin

 

[Punx0r]

I'd check your 36V controller and see if it will handle around 48V (it may well be good to 60V).

If so I'd wire in another battery in series, something cheap like 3S or 4S Lipo, 10Ah to keep up with your current 9Ah battery. Having it connected all the time will give you extra usable battery capacity (more range if you don't go any faster) and will reduce the sag you currently have at a given speed.

Going faster will require more power, so it depends if your current top speed is being limited by available power, or voltage (motor at near top speed).

Realistically there are a lot of things you can do and I'm sure people will suggest a variety of options

Ant

 

[mlt34]

I'd say the simplest option would be to have a small, higher voltage pack that you switch to when you want to go faster. A 12s 5A zippy shouldn't cost too much. You'll just need to make sure your controller can handle the increased voltage. Usually you can run a 36V controller at 48V no problem, except that the low voltage cutoff won't work for the higher voltage obviously. If you're using lipo's, that will be important to make sure you don't discharge them too much.

 

[dnmun]

if the guy is not familiar with lipo and then you tell him that all he has to worry about is the LVC on the controller then it is unfair. bulk charging lipo blind is a risky endeavor.

it is better to give up drinking for a month and use the $500 saved to buy a new lifepo4 pack.

 

[mlt34]

if the guy is not familiar with lipo and then you tell him that all he has to worry about is the LVC on the controller then it is unfair. bulk charging lipo blind is a risky endeavor.

it is better to give up drinking for a month and use the $500 saved to buy a new lifepo4 pack.

This is very true, good point. I guess I assumed he would hit the reference section to learn about 'responsible lipo ownership' (sounds like a 50's educational video) but perhaps that was a dangerous assumption on my part...

 

[dnmun]

i just think that people who recommend lipo to everyone should consider the limitations a lot of people have.

the guy who recommends lipo the most doesn't even use a method's type solution while charging.

i may be the only person here who has had to put out a house fire started from charging lipo so i am the most sensitive.

 

[mlt34]

oh wow, yea I haven't been in the lipo-fire fighting business yet, but I definitely see where you're coming from. And it's important for the OP to realize those risks. Good call.

 

[UKebiker]

Thanks all - I had rules out lipo for two reasons. One is the dangers as highlighted and other is the cost as buying 44.4v of lipo bricks, a decent power supply and a meter to monitor on the road ain't cheap !

That's why I thought perhaps a 12v nicad or even 12v of lifepo4 prismatic cells as booster might be a good idea

 

[leffex]

That's why I thought perhaps a 12v nicad or even 12v of lifepo4 prismatic cells as booster might be a good idea

Another guy proposed 3s or 4s in other words about a 12v "booster battery".

Your new higher voltage is limited by the controller. (A 36v controller are often limited to 63v or 50v.)
The hub motor is limited by the amps.

I'm also thinking of a booster battery. Is it really this simple? Arrange a bypass switch to the "booster battery" inline with the other battery. Being changed by a switch making a choice of 36v original battery or 48v so to say with the booster battery of 12v switched on?

:lol:

 

[Punx0r]

Hobbyking lifepo4?

Why switch the extra pack in and out rather than run it in series at all times? The throttle will still give 0-100% variable speed as before, but you'll have more capacity and less stress on the main battery.

 

[dogman dan]

How many drill packs do you have?

If you can paralell 2 of the 12v ones, that should do the trick to add 12v more in series for about 2-3 miles. You'll only get about 1.5 mile per drill pack you add, and of course the existing controller would have to be capable of 12 more volts. If it has 63v capacitors inside it, chances are it can. But lots of low amps 36v controllers have 50v caps. If so, you could add only 6v more. Idealy, you'd put 3-4 drill packs in paralell to get both the range and to go easier on each pack.

Aside from drill packs or perhaps a 12v sla, chances are anything you buy will mean buying a charger. One good option would be to buy some A123 round lifepo4 cells. Then to charge them, you'd likely need the same RC charger that you'd use for RC lipo. Sorta makes whatever you end up doing lead to the same place. Buy a lipo charger, which could also do lead, lifepo4, nicads, whatever.

Cheapest option of all might be 12v lead, especially if you have a 2 amp car battery charger already.

 

[d8veh]

Whatever booster battery you have, you'll need a charger for it. Your present battery has 40 off 18650 cells in it in a 10s4p construction. I think that they're Panasonic CGR18650CG, which you can buy fairly cheap on ebay. For each additional group of four, you get a 10% increase in speed. I reckon that your controller will safely handle 12S, so that's 8 additional cells. You will therefore need a charger capable of charging 2S. This one should do it:
http://www.ebay.co.uk/itm/RC-B3-LiPo-2-3S-Cell-Battery-Balancer-Charger-7-4-11-1V-Power-Cable-New-/200680431210?pt=UK_ToysGames_RadioControlled_JN&hash=item2eb97c5e6a

So all you need to do is cut one of your battery wires, solder on a Deans or powerpole connector; buy 8 cells (ideally already welded in 2S4P,; solder on power leads with a matching connector; solder on your balance leads through which you'll charge; stick them in a little saddle bag. That's it. If you want to take a chance, you can add another 4 cells foe 13S, but there's a high probability that your controller will smoke. I think 12S will give a nice balance of speed and power from your motor.

These guys do the welded ppacks:
http://www.ebay.co.uk/itm/for-Panasonic-CGR18650CH-CGR-18650-3-6V-2250mAh-10A-Power-Battery-Lithium-Li-ion-/320950697120?pt=US_Rechargeable_Batteries&hash=item4aba26fca0

You will also need a voltmeter on the pack to check that it doesn't go below 3.3v per cell (6.6v total).If the new cells are an exact match, your battery BMS will shut down when LVC is reached, but you need to check initially in case the Chinese ones are cheap copies and don't match the capacity of the others.
http://www.ebay.co.uk/itm/Waterproof-Digital-Voltmeter-DC-15V-To-120V-Red-Led-Voltage-Digital-Panel-Meter-/180888615101?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1dcd38bd

or you can use a lipo alarm, which not only shows the voltage, but beeps when you've gone too low
http://www.ebay.co.uk/itm/1-NEW-RC-2-in1-LED-Tester-Alarm-for-LiPo-Battery-voltage-tester-/380593494787?pt=UK_ToysGames_RadioControlled_JN&hash=item589d23db03

 

[UKebiker]

D8veh - thank you so much , that's what I really needed

I have two identical controllers Si u can afford to take a risk. Once !

Perfect shipping list, will report back if any interest

 

[d8veh]

To complete the list, you'll need this balance lead to charge and balance your booster pack:
http://www.ebay.co.uk/itm/Lipo-Balance-Lead-for-repairing-battery-pack-3s-JST-XH-male-3-cell-11-1V-22AWG-/230897698070?pt=UK_ToysGames_RadioControlled_JN&hash=item35c2934516

 

[UKebiker]

All the bits have arrived , can anyone advise where to solder balance leads

Not done this before


Thanks in advance

Photo of all parts , leads have 4 wires and pack in 2s4p ready welded here

 

[dogman dan]

Start with the whole packs negative terminal. that is #1 wire. That is the negative wire of the pack. On the Jst balance wire pigtails, it's the black wire.

The next wire will solder to cell one's positive, which is also the negative of cell two. The next wire connects to the positive of cell two which is the negative of cell three. The last wire is the red one, which is positive of cell 3.

You have 3s jst wires it appears, which have 4 wires. So make 3s strings. A "cell" is any single cell, or group of paralleled cells.

I see a picture of four cells in a "pack" it cannot be 2s 4p, since that would require 8 cells. It could be 1s 4p, or 2s 2p, or 4s.

 

[UKebiker]

Thanks dogman but it is 8 cells

Here is a better picture

 

[dogman dan]

Ahh, better picture worth a thousand words. I thought maybe you had typo'ed and it was 1s 4p.

You'll have to peel off the covers on the ends to access the places to solder on your balance wires. 2s packs need a 3 wire jst plug. So you might be needing to do some re arranging to make 3s 4p packs. Or make 4s 4p packs with two of them, which would require 5 wire jst's.

 

[UKebiker]

Thanks again - I def want 7.4v 9ah (2s4p) to match my 9ah 36v pack of same Panasonic cells

I've ordered them - will return when they arrive and post pics of the welding

 

[UKebiker]

Here is the welding (top then bottom )

View attachment 1

 

[UKebiker]

Ok my 2s balance leads have arrived.

3 wires - red, black and blue

Where to put them??

Many thanks - as ever

 

[ev tocak]

Ok my 2s balance leads have arrived.

3 wires - red, black and blue

Where to put them??

Many thanks - as ever

 

[UKebiker]

Wow ! Thanks Even I can't get it wrong now (famous last words)

 

[d8veh]

Before you connect to your charger, make sure that the "+" and "-" are the right way round for your charger. Don't go by the colours. With the battery connector facing you and the bits the tangs upwards, the "+" should be on the right. You can use a meter if you're unsure.

 

[UKebiker]

Here is the finished booster pack. Charge of 7.27 out if the box . Each cell the same voltage exactly.