need help wiring headway 38120S 10ah lifepo4 cells

[markmm]

hey smithmal,

"I'm assuming since you bought 38120 batteries from them they ship to the US."
>>>>yep, from china, ~2-3 weeks to get here (ga)

"In terms of quality, were you ever able to confirm that GWL's stated capacity of these batteries (8Ah) before adding them to your battery array and if so, were they "as advertised." "
>>>>as far as I can tell they were as promised and have held up and taken a charge w/o any issues so far

thanks all

 

[smithmal]

So I'd like to build an 80Ah battery using 38120S batteries. The batteries are LIFEPO4 Headway 38120S, 8Ah, 3.2V 25C.

If I understand correctly, this would mean creating a 4S10P battery correct (i.e. 40 total batteries needed)? That would give me a 12.8V 80Ah battery right?

The dimensions of a 38120s battery is 1.5" wide by 4.72" long. I need the pack to be equal or less than 12" x 12" x 12". How should I arrange all the batteries in the pack to fit this dimension?

I'm thinking the best arrangement to fit my power box with be to build two 4s5p (40aH) batteries and then add them in parallel.

Thoughts?

Thanks,

smithmal

 

[e-beach]

Hey Smithmal. First things first.

Start a separate thread of your own so the process can be addressed outside of this thread.

As for 38120s cells they usually have plastic holders that determine dimensions.

4s is about 12.8 nominal and 14.6 full charged.

Anyway, piggy-backing your question in someone else thread is ok, but better to start your own.

 

[markmm]

hey Smithmal, I saw e-beach's post and he is prob right abt starting a new thread, but mainly bc I have exhausted my knowledge and the other dudes on the board would know more and help you better than I could, for sure. I did mine by hook or by crook and it works but there may be a better way. that said, my pack is 10aH batterys if I recall and I used those little orange, plastic snap/grouping things to keep them together in a nice fashion, but I am not sure you can get all the batts you need into a 12x12x12" space, but maybe. mine is one long linear thing, you can see some pics in earlier posts but its abt 8" wide by 28" long id say, and I have it hooked up to a solar charge controller and then to a 50watt solar panel. jim at headway-headquarters.com really helped me a ton and he said:

After you have 16 good cells and they are all at 100% SOC, then build your 12V 40Ah battery. Attached is option 4 and 5 (lol) a quick drawing of 2 ways of how to wire up the 12V40Ah battery. There are a few other options, but these are the basic configurations.

What you have in option 1 is a 3.2V 160Ah battery, and from a guess, option 2 almost looks like a 24V20Ah battery but the connections are still not right for that.

 

[markmm]

jim's handy drawings that helped me

https://www.dropbox.com/s/lef2qj30msjx29q/2.jpg?dl=0

https://www.dropbox.com/s/k5ua4afhdti2gmo/1.jpg?dl=0

 

[pac2722]

OK I'm the same I have 11 of them & need to set them up to 12v or 13v I was told to run 2X sets of 4 but I get more then 20v how do I set them up

 

[amberwolf]

OK I'm the same I have 11 of them & need to set them up to 12v or 13v I was told to run 2X sets of 4 but I get more then 20v how do I set them up

If you are using headway cells, they charge to a max of around 3.6v.

Four in series is only 14.4v.

Either you don't really have just four wired in series, or you have overcharged them by quite a bit.

Please attach pictures of exactly how you have them wired, and describe/show your charging setup, so we can help you figure out where your problem is.


Side note: If you have 11 of them, you will have three unused spares that cannot be connected or used in the pack.

 

[pac2722]

OK I have never run them b4 I'm just getting them ready for my son's kids electric car I'm going to put some audio in it

 

[pac2722]

Here r some pics

 

[amberwolf]

Well, that *looks* like 4 in series. It does look like you still have protective blue plastic wrap on at least one busbar, though, and that needs to come off to make proper connections for current to flow well.

Your meter says 13.28v, which is a bit over 3.3v each, which is normal, so I don't understand where you are getting over 20v? Can you post exactly how you are measuring that?

 

[pac2722]

If I run the 2X 4 sets together I get over 20v I need to run 2X4 sets but need end voltage to b 13volts

 

[e-beach]

If I run the 2X 4 sets together I get over 20v I need to run 2X4 sets but need end voltage to b 13volts

2X 4 sets?...... Please study the proper phrasing for battery building. Are you speaking about 2S 4P (2 in parallel, 4 in series?) or are you talking about 4p 2s? (4 in parallel 2 in series?) Your numbers don't add up. Now, to get over 20v with Headways, even fully charged you need to go at least 6S.

If you want something like 13v, (12v to 14.6v) then you simply need to to use 4 cells in series.

 

[amberwolf]

If I run the 2X 4 sets together I get over 20v I need to run 2X4 sets but need end voltage to b 13volts

If you are putting them in series, then it is not 4 anymore, it is 8, which gives you twice the voltage, at 26.56v (assuming both are exactly equal).

You must put them in parallel, which means hooking the two posts you are measuring with your meter to get 13.28v on the first set to the same two posts on the other set.

You *must* put the + post to the other + post, and the - post to the other - post, to do this.

If you do not, you may start a fire you can't put out.

Before you connect them, make sure both sets of four are the same voltage, within around 0.1v or so, to reduce any sparking or heating of connections/cells.



As a side note, if you are only getting 20v, or a bit above, it means that one of your packs is much much lower in voltage than the other, which means either some of the cells in the second pack are very very low in voltage or actually completely dead, or it's wired differently than your first pack pictured above. (because 20v minus 13.28v is only 6.72v, which divided by four cells is only 1.68v, which would be a very dead cell, possibly even damaged.



If it helps, and you need something to make a "simpler" to handle pack, you can buy square busbars with four holes (instead of elongated ones with two), designed specifically to make paralleled sets like you want. Tell the place you bought the cells from that you want the rigth busbars to build a 4s2p pack, and they should be able to sell you the rigth pieces.

Then you would unbolt the cells from the busbars you have, and use the new ones instead. They'd look something like this:
https://zenid10.wordpress.com/2011/07/10/building-a-lifepo4-lithium-pack/

They also have cell holders (the orange blocks in the pic above) to keep everything rigid so nothing moves around or shakes loose, and so cells cannto short against each other if vibration causes them to rub on each other and wear away the covering on the cells.

 

[nbtesh]

Cheap chargers often end charging at 14V. As a result the LFP batteries are not charged sufficiently. In order to charge to full you need to reach above 16V.

LFP (LiFePo4) Max Charging Volt 3.6V * 4S = 14.6V

At 16V (you will blow your cell's shutoff valves and possibly cause a Fire