Taking the LiFePO4 plunge

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ChrisB
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Postby ChrisB » Fri Aug 14, 2009 7:05 pm

Thanks Jeremy for that, Ping has also come back to me and answered all my questions and the lack of paper work is apparently due to the Customs folk in China.

Any how heres a few pics of my new toy......

Its arrived in a well packed box

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I with removed the main packaging but wasnt sure how far I should go :oops:

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Got brave and removed the rest to make it look like the picture on e-bay, the charger PSU is just in the front...

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Close up of the BMS board....

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Close up of the BMS running showing the cells are fully charged all bar the far one on the left which hadnt illuminated at that time, telling me that it still needed more charging.

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Just got to fit to the bike now 8)

ChrisB
I reject reality and substitute my own !!!!!!

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Jeremy
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Postby Jeremy » Fri Aug 14, 2009 7:32 pm

I look forward to the review of it's performance on your bike, I reckon you will be pleasantly surprised!

My 36V 10Ah Ping pack is now about 18 months old and every bit as good as it was when I bought it. It even powered a 16ft boat around Cardigan Bay a few weeks ago, as a power source for my experimental electric boat project.

Jeremy

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Night Train
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Postby Night Train » Sun Aug 16, 2009 3:13 pm

It's weeny! :lol:

I hope it works well for you and I look forward to the reports of its progress and usability.

I have been weighting up how much battery I need in the MR2 and I am looking at around 45 180Ah LiFePo4.

I've figured that the £/Ah cost is about the same regardless of capacity so I just need to balance pack voltage and the physical size and weight of the pack to fit it in the car and the cost of shipping and duty etc.

Either way it will be costly so I am hoping that the conversion will be slow enough for the prices to come down a bit further.

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ChrisB
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Postby ChrisB » Sat Aug 22, 2009 4:20 pm

Right got the pack fitted after a fashion :oops:

Not that pretty currently but due to time issues I wanted to start using it rather than have it sat about.

I've got some more pics later but for the time being does any one know what sort of voltages is it likely to show when fully charged and fully flat.

My understanding is the BMS will shut it down when its flat anyway but whats the voltage likely to be when it does this, I just dont fancy being 5miles from home when it dies :lol:

Currently the bikes normal power meter just sits at max power all the time but then thats calibrated to a SLA discharge pattern and I suspect the discharge voltages are totally different compared to the SLA pack ?

ChrisB
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Jeremy
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Postby Jeremy » Sat Aug 22, 2009 4:37 pm

The voltage will stay a bit flatter with LiFePO4 than with your old SLA, so you're right, the bike "power meter" will probably not be that useful. Fitting a Watts Up or Cycle Analyst is a pretty good idea, as this will show how many amp hours have been taken from the battery, along with some other useful information.

Fully charged and hot off the charger, you should get around 3.65 volts per cell, so around 29.2V for your 24V nominal pack. This quickly drops off charge, to a cell resting voltage of around 3.25 to 3.3 volts, around 26 to 26.4v for your pack. Under load the cells will drop to about 3.2V per cell (25.6V for the pack) and stay there until nearly flat, when they will drop quite quickly down to the BMS cut-off point of around 2.5V per cell.

Using a volt meter type power indicator isn't very useful with these cells, because of the flat discharge curve. Your best bet is to either get a Watts Up or Cycle Analyst or do some range testing where you can ride home from the point where the pack runs out. You'll find that the pack capacity will slightly increase over the first few charge/discharge cycles, so if you do a calibration range check now you should have a bit of power to spare in the future.

You can buy a Watts Up in your local model shop, or from one of the on-line model shops. The Cycle Analyst is sold by ebikes.ca from their on-line shop.

Jeremy

Jeremy

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ChrisB
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Postby ChrisB » Sun Aug 23, 2009 10:07 pm

Well so far so good, took the bike for a good few blasts over the weekend and todate the battery hasnt even flinched 8)

Must have done a good ten miles today and at full bore :shock: got back home and it was still felt like it was fully charged 8)


Jeremy wrote:The voltage will stay a bit flatter with LiFePO4 than with your old SLA, so you're right, the bike "power meter" will probably not be that useful.


That would explain the full power feel during the whole journey, where as with the SLA's you notice the voltage drop off.

Jeremy wrote: Fitting a Watts Up or Cycle Analyst is a pretty good idea, as this will show how many amp hours have been taken from the battery, along with some other useful information.


What :shock: more expense :shock: , crumbs these LiFePO's are quite money hungry arnt they :lol:

Jeremy wrote:Fully charged and hot off the charger, you should get around 3.65 volts per cell, so around 29.2V for your 24V nominal pack. This quickly drops off charge, to a cell resting voltage of around 3.25 to 3.3 volts, around 26 to 26.4v for your pack. Under load the cells will drop to about 3.2V per cell (25.6V for the pack) and stay there until nearly flat, when they will drop quite quickly down to the BMS cut-off point of around 2.5V per cell.


Cheers Jeremy, thats REALLY useful info for a LiFePO virgin :oops: :lol:

Jeremy wrote:Using a volt meter type power indicator isn't very useful with these cells, because of the flat discharge curve. Your best bet is to either get a Watts Up or Cycle Analyst or do some range testing where you can ride home from the point where the pack runs out. You'll find that the pack capacity will slightly increase over the first few charge/discharge cycles, so if you do a calibration range check now you should have a bit of power to spare in the future.

You can buy a Watts Up in your local model shop, or from one of the on-line model shops. The Cycle Analyst is sold by ebikes.ca from their on-line shop.

Jeremy


Looks like another purchase is coming up then :wink:

Crumbs these LiFePO's need a lot of stuff, and there was me thinking it was just a case of bunging them in :lol:

The quest continues, but early signs are looking VERY good

ChrisB
I reject reality and substitute my own !!!!!!

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timpootle
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Postby timpootle » Mon Aug 24, 2009 9:31 am

NIce one Chris. You've made more progress than I have. Ten miles! My stack is still sat in a big heap in the middle of the garage. Making a little headway now, though. And your BMS actually Manages the Battery. Good choice with Ping, I think.
Tim Crumpton

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ChrisB
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Postby ChrisB » Mon Aug 24, 2009 6:29 pm

Cheers Tim

Well you could take a couple of your batteries for a spin round the block in the back of another car, just to say some have moved :wink:

Your set though are slightly on a different scale to my iccle one mind you :oops: but hey I gota start somewhere eh :)

So far so good, although it does seem weird having a set of batteries with such a flat voltage discharge curve and having to look at the Ah to get an idea of their status , really bizzare in my book.

ChrisB
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ChrisB
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Postby ChrisB » Wed Sep 09, 2009 8:03 pm

Finally done a thread on my Electric Bike LiFePO4 version HERE

ChrisB
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phil shepherdson
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Re: Taking the LiFePO4 plunge

Postby phil shepherdson » Fri Sep 11, 2009 8:36 am

ChrisB wrote:Well after much thought and investigation I'm going to go modern :shock:


Thanks for sharing your experiences ChrisB. I was interested to see what Ping batteries look like and how professional they are, knowing some Chinese stuff is low on quality. I have a Li 10amp/hr battery on my e bike kit and it only drops down a bit after 15-20 mile stint or two. However i do cheat by peddling to keep the speed up (av 17 -20 mph and this i swear seems to charge the battery up because the battery meter seems to move up a notch or two after that!

Phil'TNorth


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