BMS facts and how to charge lifepo4 without it!

[JUICED]

Thanks for the feedback!


Juiced

[JUICED]

Here is the set up before I added the Molex connector joining all of them.

Nice and easy to keep an eye on it.

I have since marked them so I know which Pack is "acting up"

New chargers 0071a.JPG

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Juiced

[morph999]

what does the molex connector do?

[JUICED]

I have a 9 pin Molex connector. It make it easy to plug in the 8 chargers into anything I have wired correctly.

http://en.wikipedia.org/wiki/Molex_connector


Juiced

[pgt400]

Ed, I just checked out your page...you build some cool stuff guy! My garage and basement are full of projects...hovercraft, rc helis/planes/cars, e-bikes, quads, moto-xers. I'm also looking at using solar panels this year for the bike. Probably go with 400watts of panels and deep cycle batterys but also looking at the small grid tie inverter which would likely be more eff. Side note...20" plus of snow today in NJ!

[JUICED]

Thanks and OUCH Too much Snow for me.
I will post more photos of the battery boxes as get the wiring all cleaned up.

Imagine using Headway batteries in a 1/4 scale RC car..... Got 3 I am finishing up.....

Too many projects!!

Ed

[Barry]

Interesting to see I’m not alone in struggling with BMS and charging issues.

I have tried two BMS’s on my Headway 48v 10ah pack that I built. The low voltage cut off worked on both of the BMS’s, but neither would allow for a full charge of the pack. Both BMS also did a reasonable job of protecting the batteries form overcharging. None of the cell voltage exceeded 3.9 volts during charging. The problem is when charging through the BMS a number of the cells never charge above 3.4 volts. I tried charging without the BMS but ran into overcharging issues.

My short term solution has been to use the BMS for low voltage discharge protection and high voltage charge protection. In addition, I periodically balance the pack with a single cell charger.

I recently built a Goodrum/Fechter BMS which I am going to use in rebuilding my 48v Headway 10Ah pack into a 20Ah pack. Hopefully this will result in a worry free, fully charged, balanced, protected pack.

Glad I read this thread. I like the idea of monitoring the voltage of each cell. I’m going to buy a couple cell log voltage monitors. This will make it a easier to test and monitor cells while they are installed in the bike. Unfortunately my installation design doesnt allow for easy removal of the pack. A problem I will address in my next modification.

Question: I have tested the voltage and amperage of my charger to make sure it was working up to spec. I noticed that it has three potentiometers built into the board. One POT controls the voltage and one controls amperage. Does anyone know what the third POT is for? The charger is a LiFePo4, 48 v, 4A made in china charger.

Barry

[JUICED]

"Question: I have tested the voltage and amperage of my charger to make sure it was working up to spec. I noticed that it has three potentiometers built into the board. One POT controls the voltage and one controls amperage. Does anyone know what the third POT is for? The charger is a LiFePo4, 48 v, 4A made in china charger."

I have couple of the 72 volt versions. Not sure what the other does either and trying to find a schematic is near impossible.

I have watched the charging profile of these chargers and mine will charge to about 3.60 (just like the small ones) per cell and then ramp up and down until all the cells are at maximum. You may want to leave it on longer?

I have not had any issues with the chargers, just the BMS units.

The new and improved (Headway provided) units seem to have gotten better, but due to how I have the bike wired now I will keep the setup I have.


Juiced

[JUICED]

Here is the battery Pack with the Headway installed BMS.

As you can see, not the best setup for a vibrating motorcycle.

We will be fixing That!!!

In the box is the older version BMS. Good for charging, but not enough capacity for the LVC.
I have received new and improved 72 volt - 24 cell units that do work well. I will be selling all of the new extra units soon.

Notice the JDS installed FUSE!!!

New chargers 003.JPG

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96 batteries.....no waiting!!!!

96 Cells, all load tested and charged with the single cell units and ALL sitting at 3.33 volts ready for assembly.
They will be set up as 8S4P boxes.

lifepo4 conversion 003.JPG

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Here is the first batch of TOP plates.

**** NOTE!!!****

These cells are all slightly different size in length. Solid top plates are fine if you use the single cell to cell
jumper taps (see first photo) to keep undo stress off of the cells.

lifepo4 conversion 004a.JPG

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More Later!!!!!


Juiced

[AussieJester]

Can you give us a link?

I think this is the link http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10328[/quote]

Battery Medics are back in stock for those waiting for them get in quick only 100...mine shipped today...finally :-S

KiM

[JUICED]

Here is the wiring for the Molex connector.

Molex con wiring 1.jpg

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Here is the bottom with the new wiring...MUCH less wiring.(see above photo)

Conversion part 2 3.JPG

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and the top view

Conversion part 2 004.JPG

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More later!

Juiced

[JUICED]

Here is the box being charged with the "NON BMS" system.

and the Cell Log telling me I need to charge more!!!!!

conversion 4 003.JPG

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More later!!!

all comments (constructive ones anyway) and questions are welcome!

Juiced

[Barry]

Nice looking industrial strength connectors and bolts.

What gage aluminum did you use? Did you build the battery cases or did they come with the batteries?

Barry

[JUICED]

Hello Barry,

The aluminum is 1/8 inch plate cut to size and boxes were original from Headway.


Juiced

[scriewy]

pic maybe better....

bat con.bmp

am i suppose to look at this from left to right ? i was looking from right to left every time i approached it to try to understand it but couldnt figure it out, and today after few tries in few days my head said holy sh*t i can look from the other side, it makes more sense, looks like parallel charging ? (just making sure, i must make sure cos if it took me few days to see it from another angle maybe im still missing something). i forgot to notice or more correctly my head didnt brought this fact up from my memory to my attention that i should look at positive negative leads and follow a revers flow of electrons HA HA.

All Lithium-based chemistries don't have this "self-absorption" capability, so when the first cell is full, that's it, no more current flows to the rest of the cells. By adding a shunt circuit to each cell, a certain amount of current can bypass the full cell and flow through the shunt, so that it is available for the next cell in series.

technical question just trying to understand the work of it, when the cell is full it got 3.65v back EMF against the charger, does the current diverts because the cells BEMF repelles it so chargers current starts flowing through the shunt which is with less resistance, and the cell in this case is like an electrical type of shunt ?

and chargers usually hit bats with more volts, so if total voltage of drained 10s LiFePO pack is 25v and the charger is 40v how is the charger doesnt kill cell by cell, charging first cell full and continuing to overcharge it cos it got more volts to overcome cells 3.65v resistance, is there some component that divides the voltage from the charger ?

if there is something that divides the voltage for the cells anyway, wouldnt it also work with simply having a 4v charger with high amps and BMS that parallely charges the cells ? (im thinking laymen-y here, volts stay same in parallel, amps divide)

or it just complicates the circuitry more this way ?

lets see what other stupid questions i have , general 1, those balancing boards mentioned earlier, when they are connected to 1 of the charges as icharger, GT A8, turnigy, the balancing bleeds the higher SOC cells ok, but does the charger kicks in again and again after every bleed to top the high cell till the lower catches up, or it simply bleeds the high cell lets say from 3.6v to 3.3v because the lower cell is at 3.3v and all operations stop ?

i saw stand alone balancing boards i think, do they just bleed the top cells to match lower cells so a user could start a charge with level SOC cells ?

are there stand alone balancing boards that dont just bleed but actualy transfer current from cell to cell for balancing ? (i think i saw something like that because it was said the board balances at 300ma and takes 80ma for operation)


say thanks to the guy who linked me to this thread, if i wouldnt read this i wouldnt have the new stupid questions

[dnmun]

the shunt transistor turns on and diverts the current around the cell and through the shunt resistor when the cell reaches full voltage. the resistor divider bridge is under the black goop and you can see the spots on the other side where they add a few resistors in parallel at final test to calibrate the shunt switching voltage exactly. you will see a, b and c for the extra resistors used to calibrate it. as i recall.

[Hirpm]

Maxwell,
Thanks for the great tutorial! I'm sitting here waiting for the USPS delivery today of my first Lifepo4 Pack. I just learned everything I need to know! this website is a great resource for the technology of the present and future.

Been running Lipos and am tired of spending more time with my chargers than my bike.

Gotta go, the mail truck is here (really) Thanks again!

[MountainSufi]

Maxwell,

Thankx for all the work you did on this post. I intend to search out everything you've done here at ES.

As a future owner of your upcoming frame, I must admit: I AM AN IDIOT WHO BARELY KNOWS HOW TO POST IN RED WHEN IT COMES TO ES AND EBIKES! I'll certainly use both a BMS and regular cell checkups. I admire the ebike geeks who've made DIY possible, but will never spend my time knowing all the details. I'd rather invest free time in playing with my high end stereo and GF.

Thankx again.

[JUICED]

?????????


Yes, you seem to be an idiot. (and do not take this statement lightly)

[MountainSufi]

Juiced,

If you reread previous posts on this topic you'll see I was happily informed about BMS facts, and that there was a discussion about posting in LARGE RED. I was complimenting Maxwell for his info. You missed previous dialogue and focused only on my reply. Whether or not you get my sense of humor, I take flames very, very, exceedingly lightly.

Drink good beer and...

Happy Trails!

[JUICED]

I agree that I miss read your post.
For some reason I have not been notified on a regular basis via email that other posts
have been made to this thread.

Maybe a better indication that is was humor would have helped as other folks visit this site and roam the pages too?

One of the reasons I had not been here too much was all of the squabbling. I mistook your fun as some of that....

First round of beer is on me!

[MountainSufi]

Howdy from Jackson Hole!

Due to the beauty of ES, I've checked out your posts and know you're not a trouble maker. You're my first entry to ES "friends". I'm posting this publicly so that the community can see we're cool with each other, and that things are much deeper and better than they would have been without a very minor spat.

I appreciate your advice to give more hints of my self deprecating sense of humor. In addition to fascination with ebikes, we undoubtedly both share a dislike of large RED type and emotocons

At any rate, we live in a small log house just south of Grand Teton/Yellowstone parks. If/when you and friends visit out beautiful area, you're welcome to camp in our yard with full access to the house. I'd be honored to buy you 3 too many beers at what many argue is the best small brewery in America: http://www.snakeriverbrewing.com/. Do not forget or take this invitation lightly; it's perpetual.

Thankx for making the world a greener and more fun place.

Happy Trails!
MountainSufi

http://www.jacksonholetantra.com/

[JUICED]

Thank you for the great invite! I am sure we could have some spirited discussions on may a topic.

You are also very welcome here on the coast of SC where the morning sun warms you face and beer here is also cold, ( but not as local! )


Take care!


Crazy EV Ed

[johnnymoped]

Hi everyone,

here is the complete question:

I have a 48 volt BMS that i would like to use on a 36 volt battery pack.

Would it be possible to simply not use the "extra" wires for the cells that are "missing"?

thanks,

JohnnyMoped

[dnmun]

hacking the BMS from 16S down to 12S is more complicated but it can be done. what kinda BMS do you have? maybe someone will trade with you to solve your problem. i know how to hack most of them except the digital ones.