what LiFePO4 configuration are used in these jump start power banks?

happyguy82 · Oct 20, 2014

Hello guys,

I am unable to find this info on the public domain, however I reckon a few of us can deduce this w/o having to actually open one up.

So here's the thing, these power banks have LiFePO4 batteries which give them their high C rating and thus are able to jump start cars. Starting cars require very little energy but very high discharge hence this chemistry along with Li-Po gets the job done.

Here's my question, this power bank is rated at 12,000 mAh. I can't work out whether this refers to the capacity after stepping down to 5V for USB or whether it's the true 12V capacity.

In order to answer this, I guess we need to figure out what batteries are in these things. Since LiFePO4 puts out 3.2v per cell, it's safe to assume that it's in a 4SxP configuration; therefore it's got to have 4 cells in series but a few in parallel in order to achieve the high C rating required for cranking an engine.

Can anyone answer this for sure? Thanks in advance

[url]http://ecx.images-amazon.com/images/I/71iMl43YhFL._SL1500_.jpg

http://www.amazon.co.uk/gp/product/B00KIXSXWQ/ref=s9_simh_gw_p263_d0_i4?pf_rd_m=A3P5ROKL5A1OLE&pf_rd_s=center-2&pf_rd_r=0B8V5EPZQ325FC7MCBHY&pf_rd_t=101&pf_rd_p=455344027&pf_rd_i=468294[/URL]

Image tags removed from hot linked image - Norm

StorminMatt · Oct 20, 2014

Just looking at that picture, I can tell you that this is NOT a 12V, 12000mAH LiFePO4 battery. Or even any other type of Li-Ion battery with anything close to 12V and 12000mAH. It's WAYYYYY too small.

hazza · Oct 20, 2014

I reckon these things are based on a 3-cell series pack of about 4000 mAh. With all cells full charged up to 4.2V each, the whole pack voltage is about right for your jump start. I suspect the pack is very similar to those used in RC toys and capable of >20C.

There are lots of similar products that I've noticed recently, and my impression is that they are all based on pretty much the same principle.

Davekan · Oct 20, 2014

I know that they can easily start a car, but there is no way that that has 12000mah. See video below from different manifacture.

.youtube.com/watch?v=v_WTbDdjn2s

Dave

happyguy82 · Oct 21, 2014

Hi all,

Thanks for your responses. Yeah I doubt their capacity is that high too. They're probably 12,000 mAh at the 5V output for USB charging. Therefore the 12V capacity should be closer to 4,000 mAh.

But how does it achieve 200 CCA and peak at 400 CCA?? Even at 20C this allows the 4Ah battery to put out 80 Amps at max. Or is the CCA value false advertisement too??

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IonicBond · Oct 21, 2014

The reason packs like similar ones from Antigravity is that they are rated for a very quick-short engine start - and they do a good job of that.

HOWEVER, what guys quickly learn is that the "real" Ah rating if too small, won't power their radio or heated gloves for an hour. The generally best idea is to fit the largest lifepo4 that will fit into the battery bay.

To see how a flashlight application differs from an SLI application using the same lifepo4 cells, this thread from ADVrider is a good one:

http://www.advrider.com/forums/showthread.php?t=757934

Some of you may immediately recognize the user CY, also a flashaholic!

gofastman · Oct 21, 2014

I have a micro jumper pack and a charger/discharge that measures capacity. I can run it for a cycle or two and see what happens. What discharge rate were you looking for? The unit I have has a 2A max.
I would guess that the 400a peak rating is well above the actual C rating for the cell, but the manufacturer is banking on the inherent safety of LiFePO4 cells and the short discharge time.

happyguy82 · Oct 22, 2014

gofastman said:
I have a micro jumper pack and a charger/discharge that measures capacity. I can run it for a cycle or two and see what happens. What discharge rate were you looking for? The unit I have has a 2A max.
I would guess that the 400a peak rating is well above the actual C rating for the cell, but the manufacturer is banking on the inherent safety of LiFePO4 cells and the short discharge time.

Ohh yeah that would be great please. I'd love to know that as one of my interests is to use them to power 12V appliances. 2A sounds fine just to get an idea. Cheers.

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gofastman · Oct 22, 2014

happyguy82 said:
Ohh yeah that would be great please. I'd love to know that as one of my interests is to use them to power 12V appliances. 2A sounds fine just to get an idea. Cheers.

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Well I'm very surprised by the results!
I tested the pack at what I thought was a full charge, it was fully charged about 2 or 3 weeks ago after being used to jump a car.
the average discharge current was ~.7th
2423mah!
I'll get a graph up soon, I didn't have the USB interface connector with me this time.

happyguy82 · Oct 23, 2014

gofastman said:
Well I'm very surprised by the results!
I tested the pack at what I thought was a full charge, it was fully charged about 2 or 3 weeks ago after being used to jump a car.
the average discharge current was ~.7th
2423mah!
I'll get a graph up soon, I didn't have the USB interface connector with me this time.

Ahh brilliant. Thanks

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IonicBond · Oct 23, 2014

For powering 12v applicances, small cylindrical cells are not the right cells to use.

You'll be wasting money on a high-rate feature you aren't using, and have a lot of paralelled cells to deal with. The idea is to keep the cell-count low for simplicity and reliability.

The right choice for this application are large-prismatic LiFePo4 cells - like those from GBS, CALB, Winston, Balqon etc. They come in 20 to over 1000ah ranges and are 3.2v nominal. As always, lifepo4 uses LOWER voltages than other lion chemistries do.

For a 12v application, you only need to run a 4S set of cells. Here is an example of a 400ah bank of Winstons.

https://www.youtube.com/watch?v=oJ8AfJsOhsM

You might do just as well with only 40ah cells - depending on what you want to do and for how long. I personally run a 4S set of GBS cells for my own 2A dc application - you find them at most EV builder / dealers, but I got mine at batteryspace. Instead of being yellow like the Winstons, the GBS cells have a light-blue case with purple terminal covers.

happyguy82 · Oct 24, 2014

IonicBond said:
For powering 12v applicances, small cylindrical cells are not the right cells to use.

You'll be wasting money on a high-rate feature you aren't using, and have a lot of paralelled cells to deal with. The idea is to keep the cell-count low for simplicity and reliability.

The right choice for this application are large-prismatic LiFePo4 cells - like those from GBS, CALB, Winston, Balqon etc. They come in 20 to over 1000ah ranges and are 3.2v nominal. As always, lifepo4 uses LOWER voltages than other lion chemistries do.

For a 12v application, you only need to run a 4S set of cells. Here is an example of a 400ah bank of Winstons.

https://www.youtube.com/watch?v=oJ8AfJsOhsM

You might do just as well with only 40ah cells - depending on what you want to do and for how long. I personally run a 4S set of GBS cells for my own 2A dc application - you find them at most EV builder / dealers, but I got mine at batteryspace. Instead of being yellow like the Winstons, the GBS cells have a light-blue case with purple terminal covers.

Thanks. Yes I'm aware that what I'm trying to do isn't a good approach, however I was looking for a cheap and light solution. I think 3Ah of total energy would suffice for what I need it for

the setup that you have there could power my house with my pure sine wave inverter! Hahahahaha.

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Exit32 · Oct 24, 2014

After much research, I bought a Tenergy SideKick STORM Kit Weather Resistant Portable LiFePO4 Power Bank at Amazon. Before I pulled the trigger on this purchase, I learned that most of these so-called LiFePO4 jumper packs have 3 Li-Ion cells in series even when they're labeled as having LiFePO4 cells. My understanding is that having 4 genuine LiFePO4-chemistry cells in series is desirable for automotive jump-start applications, so I went with the Tenergy SideKick jumper kit, even though it was a little more expensive than the imposters.

The way they rate the capacity of these little jumpers is weird. I think they take the mAh capacity of a single cell, then multiply by the number of cells that are within the jump-start pack. For example my Tenergy SideKick is rated at 13600 mAh. Divide that by 4 (the number of 3.6-volt cells inside) and the result is 3400 mAh per cell. At least that's how I think they're calculating capacity. BTW, if the capacity of the pack you're considering isn't divisible by 4 evenly, then it's likely not a four-cell LiFePO4 pack.

I've had my Tenergy SideKick for about a week now and have no regrets. I've used it to charge cell phones and laptops and tested its ability to start a car on my classic 1965 Rambler American. It handles everything with ease. Highly recommended!

happyguy82 · Oct 24, 2014

Exit32 said:
After much research, I bought a Tenergy SideKick STORM Kit Weather Resistant Portable LiFePO4 Power Bank at Amazon. Before I pulled the trigger on this purchase, I learned that most of these so-called LiFePO4 jumper packs have 3 Li-Ion cells in series even when they're labeled as having LiFePO4 cells. My understanding is that having 4 genuine LiFePO4-chemistry cells in series is desirable for automotive jump-start applications, so I went with the Tenergy SideKick jumper kit, even though it was a little more expensive than the imposters.

The way they rate the capacity of these little jumpers is weird. I think they take the mAh capacity of a single cell, then multiply by the number of cells that are within the jump-start pack. For example my Tenergy SideKick is rated at 13600 mAh. Divide that by 4 (the number of 3.6-volt cells inside) and the result is 3400 mAh per cell. At least that's how I think they're calculating capacity. BTW, if the capacity of the pack you're considering isn't divisible by 4 evenly, then it's likely not a four-cell LiFePO4 pack.

I've had my Tenergy SideKick for about a week now and have no regrets. I've used it to charge cell phones and laptops and tested its ability to start a car on my classic 1965 Rambler American. It handles everything with ease. Highly recommended!

Thank you so much for the helpful response. That clears things up. I guess they mean to say it's around 13600mAh at the 5v USB output then? I'll look them up online.

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Gauss163 · Oct 24, 2014

Capacity rating is probably at nominal 3.2V

happyguy82 said:
Thank you so much for the helpful response. That clears things up. I guess they mean to say it's around 13600mAh at the 5v USB output then?

Probably not. The 12000mAh rating is probably at the nominal 3.2V LiFePo4 cell voltage, implying the pack is 38.4Wh (same capacity as 4x 2600mAh 3.7V 18650 cells).

But the above discharge test implies it is probably 12.8V * 2.423Ah = 31Wh, so 9692mAh at 3.2V, equal to 3x 2800 3.7V cells (or 4x 2100).

So the primary advantage is its high burst current. It's very weak capacity-wise for its size (status quo for high-current packs).

happyguy82 · Oct 24, 2014

Re: Capacity rating is probably at nominal 3.2V

Gauss163 said:
Probably not. The 12000mAh rating is probably at the nominal 3.2V LiFePo4 cell voltage, implying the pack is 38.4Wh (same capacity as 4x 2600mAh 3.7V 18650 cells).

But the above discharge test implies it is probably 12.8V * 2.423Ah = 31Wh, so 9692mAh at 3.2V, equal to 3x 2800 3.7V cells (or 4x 2100).

So the primary advantage is its high burst current. It's very weak capacity-wise for its size (status quo for high-current packs).

Ahh ok thanks again.

StandardBattery · Oct 25, 2014

Re: Capacity rating is probably at nominal 3.2V

I'm guessing these have to be at least 4S (maybe 4S2P, but test above seems to disprove this). I'm going to measure the OCV on a full change and I think from that we should be able to determine if it's 4S, or 5S. I don't believe 3S with LiFePo4 cells would be a high enough voltage.

onetrickpony · Oct 25, 2014

Re: Capacity rating is probably at nominal 3.2V

Here's the only one I could find that I would trust to do what was claimed:
http://www.batteryspace.com/LiFePO4-26650-PowerSport-Starter-Battery-12V-10Ah-128Wh-500A-Rate.aspx

Exit32 · Oct 25, 2014

Re: Capacity rating is probably at nominal 3.2V

StandardBattery said:
I'm guessing these have to be at least 4S (maybe 4S2P, but test above seems to disprove this). I'm going to measure the OCV on a full change and I think from that we should be able to determine if it's 4S, or 5S. I don't believe 3S with LiFePo4 cells would be a high enough voltage.

If the jumper pack really has LiFePO4 cells inside, you'll find 4 cells in series. The cheaper jumper packs use 3 Li-Ion cells in series. Just be aware that some of the cheap packs CLAIM to have LiFePO4 cells inside but don't.

happyguy82 · Oct 26, 2014

Re: Capacity rating is probably at nominal 3.2V

onetrickpony said:
Here's the only one I could find that I would trust to do what was claimed:
http://www.batteryspace.com/LiFePO4-26650-PowerSport-Starter-Battery-12V-10Ah-128Wh-500A-Rate.aspx

That's insane. An identically sized SLA battery costs just 10% of that. http://pages.ebay.com/link/?nav=item.view&alt=web&id=311057283799

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what LiFePO4 configuration are used in these jump start power banks?

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