Small Battery Bargain.....?

[JamesW]

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

 

[jhruk]

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.

 

[JamesW]

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

 

[jhruk]

"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.

 

[JamesW]

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?

 

[JamesW]

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

Any recommendations for a diode from ebay, amazon or maplin? Not sure where to get this thing from!!

 

[trex]

don't do this. You need thick wires for the large currents between batteries and controller.
The wiring is bulky and dangerous. You need a properly designed printed circuit board to make the connections between the electronic elements (diodes or FETs + resistors, capacitors and transistors) easy to follow, reliable and safe. If you need to have an additional battery, wire the second battery's output to the charging port of the first battery. As you ride, the voltage of the first battery will drop, that will cause the second battery to recharge the first battery. The resulting capacity is the same but there is much less wiring.

 

[mfj197]

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?

You can do this at the individual cell level but not if you're only doing it at the overall pack level. At the individual cell level you can parallel different capacity cells together (as long as you do the same all the way up the series chain) as no one cell will go over or under voltage. If you do it at the pack level though you would be requiring the BMS to manage serious current flows to try and maintain the correct voltages of the individual cells in the pack.

Michael

 

[JamesW]

don't do this. You need thick wires for the large currents between batteries and controller.
The wiring is bulky and dangerous. You need a properly designed printed circuit board to make connections between electronic elements (diode, FET, resistors, capacitors and transistors) easy to follow, reliable and safe.

Can do thick wire np!
Was thinking of using veru board or whatever that PCB dev stuff is called, I'm sure we've got some small scraps lying around the office - or I can buy it from Maplin I think. I'm trying to ask questions here so I don't annoy my electrical/electronic designers at work (and also because the specialist knowledge is here and I would like to relearn my electronics again and understand more for home and office!)

Problem with working in S/W dept of an electronic test house is I have access to all the kit and knowledge, but getting stuff for personal use is problematic as the costs need controlling and I can't very well steal stuff from work!

Or are you suggesting that I shouldn't be doing this FULLSTOP trex?

James

 

[JamesW]

You can do this at the individual cell level but not if you're only doing it at the overall pack level. At the individual cell level you can parallel different capacity cells together (as long as you do the same all the way up the series chain) as no one cell will go over or under voltage. If you do it at the pack level though you would be requiring the BMS to manage serious current flows to try and maintain the correct voltages of the individual cells in the pack.

Michael

So would it be easier and just as efficient to run with 2/3 packs and run them to the max just swapping them over as they die?
(I don't think I'll have the extra Ah for hill climbing then though will I?)

 

[KeithH]

I am (was?) planning to run the two packs I acquired in parallel using a very simple harness once I have worked out a convenient way to connect to the terminals.
The logic being fewer voltage sag issues.
This thread is now confusing me with talk of diodes, fuses and potentially blown BMSs.
HELP
Keith

 

[JamesW]

I am (was?) planning to run the two packs I acquired in parallel using a very simple harness once I have worked out a convenient way to connect to the terminals.
The logic being fewer voltage sag issues.
This thread is now confusing me with talk of diodes, fuses and potentially blown BMSs.
HELP
Keith

You and me too Keith - It's starting to look more complicated than I thought!

I was planning to do just the same as you, potentially adding in a 3rd full 10aH battery to the mix on long journeys from the middle of next year. I was just trying to get the electrics/electronic correct for this!

James

Is anyone able to sketch out a quick, safe, simple, (possibly expandable) schematic for us to show us EXACTLY what we should be doing between the batteries and the controller! Thanks

 

[trex]

parallel up two batteries is uneconomical.

 

[JamesW]

parallel up two batteries is uneconomical.

So solder shunts to get more current draw for hill climbing and carry more batteries to use consecutively?

 

[JamesW]

parallel up two batteries is uneconomical.

Trex, could you please define uneconomical -

1) Uneconimical in wear on batteries and thus battery life
2) Uneconomical in power out for power at charge time (so electricity costs)
3) Uneconomical relative to running one after the other
4) Uneconomical - something I haven't grasped yet.

1 & 2 relate to financial uneconomy, which is this case should not be a problem given the initial cost of the battery packs relative to a full new one. (The best price I have seen for 36V 10Ah is from Cyclecharge for about £150 without a case, and with these we can get 16Ah for less than that cost!)

3 might be more of a concern if there is a better way of getting the full capacity from both batteries whilst retaining the climbing ability up big hills.

4 - no comment as I don't know what I've missed!

James

 

[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?

Yes, that's ok. This puts less stress on both batteries, so should extend their life, compared to using them in sequence. Separate them for charging though and make sure they're at the same state of charge (voltage) when you connect them together.

 

[JamesW]

Yes, that's ok. This puts less stress on both batteries, so should extend their life, compared to using them in sequence. Separate them for charging though and make sure they're at the same state of charge (voltage) when you connect them together.

How close do the voltages need to be? +/- 0.5V 1V 0.1V...?

Looks like we're getting some differences of opinion here now,
most seem to agree that it is possible to parallel up the battery packs and would probably not be suggesting so if it was not desirable, however jhruk seems to directly disagree with trex who seems to think that you wouldn't want to parallel up the packs due to it being uneconomical.

I'm confused by trex's stance as I have come to respect his knowledge over the last month and I'm wondering what he knows that we don't. Especially confused by trex appearing to take a different standpoint to shemozzle!

James

 

[mfj197]

Yes, that's ok. This puts less stress on both batteries, so should extend their life, compared to using them in sequence. Separate them for charging though and make sure they're at the same state of charge (voltage) when you connect them together.

I said above that no, this isn't okay. I'm thinking about this some more, and would still maintain that it isn't advisable. The problem is differing cells (which they will be if they have different capacity) will have different internal resistance and would discharge at differing rates, if not controlled by the BMS. The BMS will do its best to maintain an equal and fair state of discharge, but when you are working with discharge currents (rather than charge currents, which are quite a bit lower) it will potentially have to be shunting significant amounts of energy around the place in each pack. I'd be reticent to put a BMS through that sort of stress.

James, it is however perfectly possible to parallel up two identical packs.

Michael

 

[JamesW]

Ah ha.

Lovely clear response with nice good logic. Now I understand. I can use either 2x4Ah or 1x10Ah but not both at the same time!.
Thanks Michael
(Like your lights by the way!)

James

 

[jhruk]

I am (was?) planning to run the two packs I acquired in parallel using a very simple harness once I have worked out a convenient way to connect to the terminals.
The logic being fewer voltage sag issues.
This thread is now confusing me with talk of diodes, fuses and potentially blown BMSs.
HELP
Keith

That's all you need to do Keith, your logic is correct.

Provided you ensure that all batteries are at the same state of charge (voltage) when connecting them together you don't really need the diodes. The most likely cause of any damage would be connecting batteries with a large voltage difference, such as a fully charged one to one fully discharged. Fitting diodes would prevent this, but they have their own problems with fitting and losses.

Here's the simple connections I'm using at the moment for testing. The connectors hold the single strand mains cable quite securely - I cover them when on the bike. I'll make some proper connectors when I have the time, but I won't be using diodes.