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Discussion Starter · #1 ·
Oh no not again.
IMG_20160220_173513.jpg
This is my new AT battery. It's a 4 cell pack of 15Ah capacity. It weighs less than 2kg and if I'm honest it scares me a little since those cells will discharge happily at 150A. It cost less than 100GBP.

Whilst bits are painted plated or otherwise fettled I'm getting on with other aspects of the build, ATM its the battery.

I'm going to start off without a management unit and install a monitor which will tell me if the cells are low and what voltage they are at. This means I need a posh charger so I borrowed an RC charger, costs about 30GBP, to charge and balance the pack if necessary.

Once it's all charged etc, I'll go start some cars with it via my nifty power meter to see what's getting sucked out of it.

I will keep you posted and hopefully not bore too many.
IMG_20160220_173412.jpg

Andy
 

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Not bored at all. It's good to see someone actually testing new kit out in a systematic way, rather than just taking advertisers' words for it. And what is acting as a starter battery now will probably be powering new bikes in a few years. Keep us posted with results, please, good or bad.
 

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Discussion Starter · #3 ·
Cool thanks for that. The commercial lithiums like shorai etc use the same chemistry but a lot less of it.
These cells are used in electric bikes and cars, but the ideal cell for starter batteries is probably the headway 38140s, a high current 8Ah cell. It's lighter and delivers similar current. I haven't got any of those and there's not much diffence in price.
 

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Hi Andy. Thanks for starting this thread. Your comments in previous threads on this topic have been really helpful for me.
I have bought a Lithium battery for my Africa Twin but not fitted it yet. I will fit it this spring, all being well.
I also have a small (*** packet size) jump starter pack that I have used from time to time on various vehicles including a 2.5 litre diesel VW camper van. The jump pack is a great piece of kit. I had to use it this weekend on a RAV 4 and I think I noticed that phenomenon previously mentioned, where the lithiums appear flat but after loading them for a while the RAV kicked into life instantly.
Regards charging and balancing. I understand the model car people apply a slow charge controlled low current for this purpose. Is there some kit I can use for my bike battery. When I bought the bike battery the seller said a normal battery charger was fine but I am not so sure now.
I do have a cheap low amp trickle charger that probably has nothing but a transformer and rectifier so I thought about trying that but done nothing yet.
Anyway, as I said, looking forward to your real world findings.
 

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Discussion Starter · #5 ·
Hi traveller. If your lithium battery has a management system in it you can charge it with a normal lead acid charger up to about 14.4v. You won't need to balance this sort of battery as its all done for you.

If your lithium battery has no BMS then you will need to be more careful but again it will need to reach 14.4v but little higher. You can only balance the cells if there is an electrical connection directly to each cell which usually terminate in a socket on the battery for balancing purposes.

With lithium batteries once a cell is charged using constant voltage its resistance goes high and it stops charging but also stops the other batteries charging in the pack. A balancer will allow the other batteries to charge to the same point by allowing current to flow around the full cell ( in simple terms)

since there are only 4 cells in a 12v lithium balancing may not end up being the issue it would be if you were making a 50v pack with 16 cells

So which lithium did you get?
 

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Discussion Starter · #7 ·
That looks like a 4aH unit. There's no balancing to be done there. Use a constant voltage if you are going to charge it. Have a good RR too.

I doubt it has any internal electronics to protect the cells.
 

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Discussion Starter · #8 ·
So, I have been doing some testing on the battery.

I haven't balanced the cells as so far they haven't needed it.

I've made up some short cables to allow me to substitute the larger car battery terminal separation and done some discharge tests.

As a point of interest lithium iron phosphate (life) cells have a usable voltage range from 2v up to the nominal voltage of 3.3v a cell although charge voltage goes to 3.65. This is very different to phone batteries and smaller cylindrical cells which have higher cell voltages, typically 3.7v charging at 4.2v. The latter cells have better energy density but are less safe than life cells and whilst life cells are tolerant to overcharging most other lithiums are not and will protest by getting hot and ultimately catching fire.

The cells I'm using have a capacity of 15Ah which makes discharging them a lengthy process but also that their ability to provide high output currents is good. Usually currents, charge and discharge are expressed as a multiple of the capacity. So for example the 15Ah cells are rated at that capacity at a discharge rate of 0.5C or 7.5A. Other factoids are that continuous discharge and charge is 3C or 45A and 30s pulse at 150A, short circuit the cell and it will pass over 250A.

You might think 250A isn't very high as some lead acid batteries claim more than that, well a lithium battery can never provide a CCA reading as the specification excludes lithiums because the cell voltages cannot drop low enough to fit the spec which is the number of amps the battery can supply at a temp of about -17C for 30s and still maintain 7.2V.
This makes it hard to compare lead acid with lithium. The internal resistance doubles or thereabouts from 25C to -20C halving its current output.
But it's easy to warm the battery as the higher resistance increases the heat produced on discharge and low heat capacity.

I digress tho. I will be testing the battery at the weekend on my AT starter and measuring some stuff which I will post presently.
 

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Discussion Starter · #10 ·
I forgot to say with all the digressing what I've actually been measuring etc.

I charged each cell to 3.65v before assembling the pack, this indicates a fully charged battery and have done some low DOD cycles. DOD is depth of discharge and will affect the number of cycles.

In the case of these cells you are supposed to get 2500 cycles at 80% DOD , that is 20% charge left and 6000 cycles at 40% DOD. So you can see you can double the life of your life (see what I did there) by keeping the charge level up. You probably won't get 18 years from your cells but its possible. I pulled some old nicads from the 90s in an Emergency light which had been left cycling on and off for 20years and passed the required tests but I had to replace them.

A lead acid battery will struggle with cycle life unless it's a deep discharge version when 1000cycles is possible at low DOD. Starter types might manage 2 to 300 low DOD cycles but its designed to start a vehicle then be charged back up, nothing more.

Anyhoo cycling the battery should show up any imbalance between the cells, but there are only 4 cells so it isn't the issue it is for modellers who have a lot of cells in a pack. Also as the capacity of the cells increase the problem is lessened as the voltage differences are, relatively, smaller for the same amount of imbalance in charge capacity.

100mAh difference in capacity on a 1Ah cell is 10% but only 1% on a 10Ah cell.

So once I know the cells are closely charged a few cycles will tell me if they will maintain balance sufficiently well for me to not need any circuitry to manage charging and discharging.

Then I can discharge at higher currents until I'm starting cars with it.

14.8 v is the max charging voltage for long life llife but it can tolerate more without anything nasty happening and cycle life will be reduced. A good regulator on your bike is important but equally, maybe more important is don't discharge the battery down past 2v a cell or 8v for the battery. For long life I'd keep it above 12v always when not actually starting something.
 

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Discussion Starter · #11 ·
Here's a couple of pics of the voltage monitor, it's about an inch wide and cycles through the cells displaying the cell number and then its voltage then finally the total voltage.

IMG_20160311_002938.jpg IMG_20160311_002959.jpg IMG_20160311_002955.jpg IMG_20160311_002946.jpg
 

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Hi, this is a question for Andy.
I haver a lithium battery I bought for my Africa Twin but have not yet fitted it. These things are new technology to me. One of my concerns is charging the battery properly and your earlier answer was very helpfull re balancing when in series and the fact that a 12 volt Lithium shouldnt be a problem.
I currently (no pun intended) use CTEK automatic chargers mostly and they are used on various lead acid batteries to great effect.
I understand that these chargers with there automatic de sulphation mode are harmfull to Lithium batteries so I am loath to use them as such.
CTEK sell a lithium specific charger, however it is around £100 so I am looking for an alternative.

I have a desk top variable voltage power supply like this W-10AM Watson 10A PSU available here - radioworld

I presume I could just connect the battery to the outputs of this unit and set it to about 14 volts. There would be no current regulation so, as I have a MOSFET Reg Rec I would fit this between the powersupply and the battery to utilise the regulator function. The input from the power supply would be through any two of the reg recs three inputs and the bridge rectifiers would sort the direction of current flow. The output would go from the reg rec battery outputs to the lithium battery. This would provide regulation of the supply in the same way the charging system would from the bike.
Have you any observations or suggestions?

Thanks
 

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Discussion Starter · #14 ·
Well, you can put DC into the regulator but it will need to be higher than 14v as you will lose 1 to 2v through the semiconductors, about 0.7 v per diode.

Lithium's like to be charged with constant current as a bulk charge and then constant voltage for the last bit. Usually a cheaper charger will limit the current and voltage together, which works fine, but its not ideal. The only real absolute is maximum voltage on a cell. For 12v its 14.8v if all the cells are the same. It won't care if it's part charged so 14v would be fine, it just won't be full.
If I recall your battery is 4aH so you should be looking to charge at about 3C or 12A and you can limit the current with a series resistance, like a headlamp bulb. As the voltage rises at the battery current will drop and charging will stop when the battery reaches supply voltage. Time to disconnect then.

Jrelecs OEM iMAX B6-AC B6AC Lipo NiMH 3S RC Battery: Amazon.co.uk: Electronics

That sort of thing will charge and balance but only if you have a balance port. You can use it without the balancing.

I'd be tempted to see what the ctec puts out voltage wise but if it you can't turn the anti sulphation thing off then you can't use it.
 
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