Small Battery Bargain.....?

Those of you who subscribe to David Henshaw's AtoB magazine might remember an article in the April issue about him using a B&Q Mac Allister 36V 4Ah power tool battery pack to power his Brompton.

 

Unfortunately his confidence that B&Q would continue to develop this system was unfounded and in the latest AtoB he mentioned that they are now discontinuing the whole system, and that the remaining battery stocks have been reduced to £34. Given that they were originally £130 that sounded as if they might be worth a punt so I went along to B&Q and purchased a couple.

 

For your £34 you get the battery pack measuring 151 x 85 x 80mm which is labelled as weighing 1.19kg. David Henshaw made it 1.24kg while my kitchen scales show 1.27kg. There's a four segment 'press to test' charge indicator on the battery. You also get a charger, which is slightly larger than the battery pack but quite light, stated at 0.67kg

 

So far I've just tested the one battery and found it cut out at around 31V, after giving 140Wh discharging at 3.5-4 A, very near the 144Wh specified. The charger is quite fast, with a stated charge current of 3.7A, a full charge taking under 90 minutes.

 

My intention is to use these as modular system for my folder but I haven't decided yet where to mount them, or whether to enable them to run in parallel. I'll need to fabricate some form of connector for them whatever.

 

If you want a small battery pack and don't mind a little diy these workout at at only £2.40 per 10Whrs, and would seem to be a bit of a bargain – only time will tell.

 

He's the B&Q link. You can't buy them online but you can check which stores have them in stock - in my area it was only the larger stores. It's not a 'Black Friday' offer but a clearance sale so I would expect them to be this price, or cheaper, until they're gone. I've no idea what happens with the two year warranty.

 

Mac Allister 36V Li-Ion 4.0Ah Battery & Charger

Edited November 28, 201411 yr by jhruk

Great link, thanks! Have you had a chance to look inside yet?

No, I'm afraid I haven't opened one up yet. I've been tempted but I intend to use them as they are and as they supposedly come with a 2 year warranty I'll try & resist, at least until I've used them for a while.

 

I haven't had time to do any more with them yet but hope to try them on the bike sometime this week.

Will you be sacrificing one of the chargers to make a bike mounting plate? How many amps do you think you might pull out of a single pack?

B&Q website states 35 minute continuous usage for the cordless lawnmower so the battery pack should be OK for approx 8amp continuous delivery (2C).

Will you be sacrificing one of the chargers to make a bike mounting plate? How many amps do you think you might pull out of a single pack?

 

No, making a mounting plate should not be too difficult, once I've decided where to put them. The second charger is too valuable, for simultaneous charging or as a spare.

 

I don't know the max current they were designed for but David Henshaw said he ran his Brompton off one pack without problem - I'd guess that would be around the 8A suggested by Shemozzle999. With my 14A controllers I've decided to run my pair in parallel. As they each have a charge indicator I probably won't bother with blocking diodes as it will be easy to check the charge state of each one before connecting.

 

I'm still undecided about exactly where to mount them. At first I thought of along the main tube, either in line or one on top and one underneath. However my current thinking is one each side (front&back) of the seat tube. I'll probably sleep on this for a while whilst I rummage around for suitable materials. They can just go in a rack top bag for the time being.

I found the lawnmower on Alibaba and the 30 minute rating was for the 2.6aH battery so the average safe constant discharge current for the lawnmower motor is probably less, approximately 5.2a. If you want to diode feed each one this might be OK to use, although it will drop the supply voltage by 0.471v and you would need to heatsink it to dissipate any heat generated:

 

http://www.onsemi.com/pub/Collateral/NTSV30H100CT-D.PDF

B&Q website states 35 minute continuous usage for the cordless lawnmower so the battery pack should be OK for approx 8amp continuous delivery (2C).

I just had a look on my local BnQ, 35 mins is for the 2.6ah one, the 4ah will run the mower for 49mins (i think it said). It may well be 2C but for that spec it only needs to be just above 1C.

I would not bother with a diode if you are going to fully charge both before each ride.

The constant current rating, I suspect may well be a fair bit higher as a mower tends to see some pretty difficult conditions at times, the difference in how long the battery lasts on ours (different 36v lipo brushless mower) can be greatly effected by the grass being an inch longer, let alone what long damp grass would cause load wise, the wife wont let ours exceed much over 2" normally, I dont mind though as she does the mowing

 

Our previous 12v brushed mower had a 400w motor (our new one sounds much more powerful) and I noticed a couple of 36v ones rate there motors at 12 to 14 amps

If you don't want to incur the voltage drop caused by the introduction of the diodes the minimum protection against any cell failures or internal faults could be achieved by fusing each output line if paralleling the 2 batteries together.

I'm either mad stupid or both coz I've just bought 2 of these! The cost per Wh is too good to be ignored.

My idea is to use them as a "reserve tank" (1960s motorcycles) on my kit Trex.

I still have a soldering iron but haven't used it for years and my knowledge of electricity is 1960s A level physics. The result if I use it may be painful in both my wallet and whichever part of my anatomy feels the heat.

I also don't want to re-invent the wheel so has anyone an idea where I can find a simple connector for the battery.

Help please

Keith

ps Enfield (N London) still have 4 or 5 on the shelves. They are labelled as £129.98 but are £34 at the checkout. They're in the gardening section.

ps I'd rather not cannibalise one of the chargers

Please can you share a photo of the battery connector and charging base?

There is quite a few down in Farnborough for those interested. I am picking up a couple (well, 3!)

Photo!?

I'll try tomorrow but I don't have a NVQ in tech

BW

K

some pictures as I am interested in connection suggestions as well

This link is to a makita battery connection, but is similar to what I have done in the past, mine used small bolts to hold on the metal tabs and connect the wires, the plastic doesnt have to be as good a fit as shown as a velcro strap will stop it moving.

Or if you are using 2 packs use a bigger piece of plastic and attach 2 sets of contacts to make a neat single unit holding both batteries.

Hope that makes sense

http://www.thingiverse.com/thing:74136

Ok - 3 quick questions...

 

1) Can I simply parallel 2/3/4/5 of these up to make a 36V 8/12/16/20ah battery? (or is it more complicated than that as each battery has it's own BMS?)

 

2) Can I charge this with my normal 36V bike charger whatever ah rating the battery ends up at? (i.e. charging a paralleled Li-ion battery if I make 1, or charging the existing 1 if I put it at is in a bike mounted battery case)

 

3) Can anyone Identify which of the 4 terminals do what please so I can connect it up correctly?

 

(Not planning on using them on a folder - planning on building a BIG battery for my conversion kit for next year to allow longer rides and lights to run off the system as well!)

 

Thanks in advance for your technical expertise!

 

James

Edited December 11, 201411 yr by JamesW

I am interested too . However, I have also now picked up a hedge trimmer using the system (battery) so will likely use the battery for its designed purpose for a while, but it is good to know that I can re-wire this to obtain a decent 24v big Ah for my old Giant Lite (currently running in NiMh).

Ok - 3 quick questions...

 

1) Can I simply parallel 2/3/4/5 of these up to make a 36V 8/12/16/20ah battery? (or is it more complicated than that as each battery has it's own BMS?)

 

2) Can I charge this with my normal 36V bike charger whatever ah rating the battery ends up at? (i.e. charging a paralleled Li-ion battery if I make 1, or charging the existing 1 if I put it at is in a bike mounted battery case)

 

3) Can anyone Identify which of the 4 terminals do what please so I can connect it up correctly?

 

(Not planning on using them on a folder - planning on building a BIG battery for my conversion kit for next year to allow longer rides and lights to run off the system as well!)

 

Thanks in advance for your technical expertise!

 

James

 

1) assuming you can identify.the output terminals you can parallel or series them ( at least I have with matuka packs) Series adds the volts, parallel the ah.

 

2) no, absolutely not. You need to charge each pack individually with the charger it came with

 

3) no, but test them. Do they all give voltage ? What voltage ? Also look inside the device ( drill etc) you may find it had only two terminals) in which case it's two to charge and two to discharge (the ones.net that match the drill are discharge)

1) assuming you can identify.the output terminals you can parallel or series them ( at least I have with matuka packs) Series adds the volts, parallel the ah.

 

2) no, absolutely not. You need to charge each pack individually with the charger it came with

 

3) no, but test them. Do they all give voltage ? What voltage ? Also look inside the device ( drill etc) you may find it had only two terminals) in which case it's two to charge and two to discharge (the ones.net that match the drill are discharge)

 

Ok point taken on item 2 - pity, It would have bee nice to box them in a pannier mount case!

 

 

flapajack - any chance of a pic of the hedgetrimmer connections for the battery please? I sent a friend to pick up the battery on the way home from work as it would be a 1hour detour for me to get one! - so I'm not sure what the actual connections are for drawing current.

 

Thanks

 

James

Ok - 3 quick questions...

 

1) Can I simply parallel 2/3/4/5 of these up to make a 36V 8/12/16/20ah battery? (or is it more complicated than that as each battery has it's own BMS?)

 

1) Yes, but make sure they're all at the same state of charge before connecting them. The built in charge indicator makes this easy.

2) Can I charge this with my normal 36V bike charger whatever ah rating the battery ends up at? (i.e. charging a paralleled Li-ion battery if I make 1, or charging the existing 1 if I put it at is in a bike mounted battery case)

2) As Kirstin says – No, use the supplied chargers

3) Can anyone Identify which of the 4 terminals do what please so I can connect it up correctly?

 

3) The two outside terminals, marked + and - , are the ones to use to connect to your controller. The inner two are used by the charger, but I'm not quite sure how yet.

 

Due to the inclement weather I haven't done much work on these but I did manage one >20mile test ride using the two in parallel with an 18amp controller. They performed as expected and encouraged me to purchase a third pack.

 

Due to the inclement weather I haven't done much work on these but I did manage one >20mile test ride using the two in parallel with an 18amp controller. They performed as expected and encouraged me to purchase a third pack.

 

"18amp controller" - please explain... I thought they were rated for Voltage and the motors for Watts?

 

i.e. I have a 36V 10Ah battery on my bike at the moment so I'm pretty sure that should I need to I could use 2 in parallel to give me a 36V 8Ah battery without damaging the system - good logic?

 

James

"18amp controller" - please explain... I thought they were rated for Voltage and the motors for Watts?

 

i.e. I have a 36V 10Ah battery on my bike at the moment so I'm pretty sure that should I need to I could use 2 in parallel to give me a 36V 8Ah battery without damaging the system - good logic?

 

James

 

Hi James,

 

Every controller has a current limiter which determines the maximum power the motor can draw. An 18amp controller with a 36v battery would limit the motor power to around 650watts.

 

I mentioned the controller rating to give an indication of the batteries capabilities, which in this case is an unknown. The maximum power the battery can deliver is governed by the 'C' rating of the cells and the power rating of the BMS. The rating of the battery needs to be ≥ the controller.

 

Confusingly these 'ratings' have a maximum and continuous value, with the continuous one usually being half the maximum. Controller values usually refer to a maximum whereas motors and batteries are often stated as continuous.

 

If you have a standard ebike 36V 10Ah battery at present I'm fairly confident you won't have any problems with two of these in parallel.

Edited December 12, 201411 yr by jhruk

Ok thanks jkruk, (I'll work on understanding C ratings in time)

 

Is it permissible to parallel 2 batteries of the same technology and voltage but different ah ratings (if diode protected) and if so what effect would this have on battery life?

 

e.g 36V 2.6Ah & 4Ah or 36V 4Ah and 10Ah. all Li-ion

 

I assume principles would apply to n batteries paralleled together?