building a headway battery pack

hello everyone, i am looking to build a headway battery pack, however i have some questions i was hoping you could answer before i attempt to take on this project, because messing things up is not what i want to do. any assistance will help however experienced pack builders are a great asset. i will list my questions by number, to help organize things, if you decide you want to answer a question please put the number of the question your answering before your answer so i can try to get the best notes possible.

1. what are the different ways i can balance the cells? and i have seen a "regulator" and a "BMS" on headways site. would you mind telling me the difference please?
2. how would i wire cells in paralell? would the cells not discharge when connecting negitive to negitive and positive to positive? and how could i balance cells that are connected to eachother like that accurately? (i am trying to build a 48v 40ah pack)
3. where is the cheapest place to get headway cells
4. what is the highest recommended battery measurement system for this application and how would i go about wiring the cells to the system (multiple systems ranked by price will help)
5. would someone mind showing me the most efficient way to build this pack? what AH cells should i use and how should they be arranged (paralell, series what combination) description would be helpfull (i intend on splitting the one battery pack across the bike for better weight distribution)
6. what should i house this battery in? something durable that will protect the crap out of the cells.

a good description will help, thank you for your time and effort.

Hey jatgm1,

I can't really answer all your questions, but I can get you started. I have been running a Headway 36v 15ah pack for several years on my bike and can attest that my Headway's have been robust and reliable. That being said lets get started.

jatgm1 said:

1. what are the different ways i can balance the cells? and i have seen a "regulator" and a "BMS" on headways site. would you mind telling me the difference please?

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A BMS is the normal way to balance a Headway pack. A good bms, properly wired is plug-and-play. It will over time (a few hours or maybe over night) balance your pack with out problem.

You could just bulk charge your battery pack, and then meter each cell voltage and and then put a small charger on the cells to bring them up to 3.65v but doing that "one at a time" cell balancing is not really practical. It is mostly used as a way to get an "un-balanced" lithium battery pack back into balance if "low voltage cutoff circuit" on a BMS has triggered because one of the cells is below the BMS's threshold. Or if you have other problems like your BMS has gone bad and you need to balance your pack while waiting for the other one to arrive in the mail.

I have never used the regulator you referenced, but I believe it is used in conjunction with a BMS to "Fast" bleed the cells so the pack can be balanced faster then the BMS can do on it's own. I believe it is for large battery pack. You may not need it.

jatgm1 said:

2. how would i wire cells in paralell? would the cells not discharge when connecting negitive to negitive and positive to positive? and how could i balance cells that are connected to eachother like that accurately? (i am trying to build a 48v 40ah pack)

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48v 40ah pack... I don't know what type of bicycle you can fit this large pack on because the pack will be in the 45lbs range. My 36v 15ah pack , DD motor and bike are 80lbs. So you are thinking about a bike in the 120lbs range depending on the motor you are running.

Do you really have over $2000 USA budget for a battery pack?

On paralleling cells, Headway's have a 4 hole bus bar system so you can parallel 4 cells together. (negative to negative and positive to positive) So for instance if you had 4 38120s cells, then you could connect them into a 3.2v 40ah unit. You could then put 16 of these units in series for a 48v 40ah battery pack. If you can not find a good BMS with 64 channels, then using a standard BMS with 16 channels
would see each group of 4 cells as one cell. You would need to periodically use you digital multi meter to check each individual cell to make sure it is in good balance with all the other cells.

Another options: Use more then one BMS or uses 15ah cells and use less cells.
Ganged in parallel the cells would not discharge much on their own, unless one of the cells in the parallel was not charging well.

jatgm1 said:

3. where is the cheapest place to get headway cells

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Probably eBay. No lithium battery is cheap these days, but the best prices are coming from China....no surprise. But, if you have a problem with your order, then dealing with a Chinese company is a risk.

jatgm1 said:

4. what is the highest recommended battery measurement system for this application and how would i go about wiring the cells to the system (multiple systems ranked by price will help)

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I don't know what you mean by "battery measurement system"

jatgm1 said:

5. would someone mind showing me the most efficient way to build this pack? what AH cells should i use and how should they be arranged (paralell, series what combination) description would be helpfull (i intend on splitting the one battery pack across the bike for better weight distribution)

Click to expand...

Headway "2 hole spacer blocks" are made to work one way. When you get them look at them very carefully and plan out your multi cell units carefully. Then assemble to your desired dimensions. Press the spacer blocks over the cells and then put the bus bars over the ends of the cells and torque them in at the specified torque value. Also consider some sort of thread lock so the screws can't wiggle loose. Note: the spacer blocks are snug on the cells so keep a block of wood around to cover the spacer block ends and tap the blocks snugly on to the cells with a small hammer. Just be very cautious not to break the legs on the spacer blocks or damage the cells. The legs on the spacer blocks are easily broken.

jatgm1 said:

6. what should i house this battery in? something durable that will protect the crap out of the cells.

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People use anything from backpacks to plastics to metal to protect their cells. Coroplast plastic sheets cut to size, taped around the batteries and then put in another container like a panier could work. It is really up to how you want to mount you batteries to your bike. If you haven't already done so look at all the pictures of other people's ebikes and see what works for you. My cells are mounted in the triangle of my frame. This is the best place for them for proper weigh distribution and balance of the bike. Putting them high on a rear rack can cause insatiability of the bike. If you have filled the triangle of your bike with cells and you still have more, then keep the weight as low as possible....like in paniers.

Edit: You might also consider a Ping battery because the Ping 48v 20 ah batteries are already split into 2 parts.
http://www.pingbattery.com/

e-beach said:

On paralleling cells, Headway's have a 4 hole bus bar system so you can parallel 4 cells together. (negative to negative and positive to positive) So for instance if you had 4 38120s cells, then you could connect them into a 3.2v 40ah unit. You could then put 16 of these units in series for a 48v 40ah battery pack. If you can not find a good BMS with 64 channels, then using a standard BMS with 16 channels would see each group of 4 cells as one cell. [strike]You would need to periodically use you digital multi meter to check each individual cell to make sure it is in good balance with all the other cells.[/strike]

Another options: Use more then one BMS or uses 15ah cells and use less cells.
Ganged in parallel the cells would not discharge much on their own, unless one of the cells in the parallel was not charging well.

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I realize this is an old thread, but for the benefit of anyone who finds it later I need to correct the above statement.

Multiple cells connected in parallel with each other act as 1 large cell. You do not need a BMS channel for each cell connected in parallel. You do not need to periodically check each cell to keep it balanced. If one of the cells goes bad early, it will be possible to tell that the cell block it's a part of has a problem, but no amount of checking the terminals of each cell in the block will give you any useful information about which particular cell is the culprit. At that point, you need to remove the cell block, separate the cells, and test them individually.

#3.http://www.headway-cn.com/en/about-us.php I bought a 24s= 84v 20ah DIY batteries (43184) from a member on ES. He got them STRAIGHT FROM HEADWAY in China, bc he had a hard time finding the 20ah ones. I am currently (pun intended) wiring these up for my XPh e-moto.
I have one QUESTION myself. Where do the charging or load wires connect to the pack? I am planning on connecting them to the FIRST cell positive and the LAST cell negative BOTTOM and TOP of each particular cell to make a COMPLETE LOOP. (or reversed, so long as it is looped) Is that the correct way? A photo would be appreciated. tnx...

The first positive post and the last negative post is fine. Make sure you torque the screws to proper torque values. Having a screw loosen while riding can cause an interment lvc problem due to the occasional disconnection of the wiring. A good thread lock is very helpful.

e-beach said:

The first positive post and the last negative post is fine. Make sure you torque the screws to proper torque values. Having a screw loosen while riding can cause an interment lvc problem due to the occasional disconnection of the wiring. A good thread lock is very helpful.

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What is the REAL correct tightening torque for Headway 38140S -12Ah? I find information contradictory:





As you can see, in one image it says 3 Nm and no more than 4 Nm and in the other image it says 5 Nm and no more than 7 Nm.

Something like picture 3 is what you want. The screw should not crush anything underneath the threaded part of the screw. Leave an air gap. 5nm (44.25 inch pounds) is fine. If you go any tighter, 7nm (62 inch pounds) you might strip out the threads on the cell and ruin that cell.

e-beach said:

If you go any tighter, 7nm (62 inch pounds) you might strip out the threads on the cell and ruin that cell.

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I have rebuilt Headways packs many times. 5Nm-6Nm is a good value. The danger of higher torque has nothing to do with stripping the threads - the threaded end plates are thick and will take substantial torque without damage. The problem is that the endplates will spin in place over the inner cell anodes/cathodes/valving. This permanently loosens the endplates with an attendant increase in resistance, heating, etc.

I recommend using a small electric drill or electric screwdriver with an adjustable torque clutch. I use a compact Milwaukee 2410-22 M12 drill/driver (non-impact) with a #3 bit and the clutch set to #1. When complete, torque all screws with the #2 setting.

The negative terminal on Headways is a accident waiting to happen because the pos+neg voltages are right there a fraction of an inch apart. A dropped or slightly misplaced busbar plate gives instant spectacular fireworks. Following the example of others, I cut insulating washers and popped them on the negative ends before adding the bus bars. Make the hole a trifle small so the washers stay in place. I cut these from heavy 40mil PVC rubber shower pan installation liner (Home Depot) using an OLFA CMP-1 Compass Circle Cutter. This grey construction sheeting comes in a 4 ft wide roll and costs under $10 a ft.

Simple split ring lock washers have kept my packs together for 15000 miles although star spring washers would arguably be a better choice.

teklektik said:

I have rebuilt Headways packs many times.

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Where do you get your Headway cells?

e-beach said:

Where do you get your Headway cells?

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Many years back I bought a pile of 38120's from Manzanita Micro. Manzanita Micro no longer sells Headways, though.

Those cells were rebuilt many times into different s&p configurations as I experimented with weight/performance/distance. Extra cells have been built and rebuilt into a number of secondary packs - simple 12V packs for common automotive accessories or booster packs for the bike.

Frankly, I was interested in the battery configuration experiments which made the Headways attractive. After that first build I switched to Li-ion and never looked back. That first bike still lugs around the Headways and runs like the day it was built, but the flexibility of the Headway configurations has long ago been replaced with a desire for better energy density.

Update on your battery pack build?
I'm new here and I'm wanting to build the same style pack too!
Currently have 30 headway cells on order.
Just trawling for answers atm, before I post my own question.

Your should order 32 or one spare 33 cells for 16s 2p. As 16s 48v and more common for bms and charger.

Teklikit it's good to hear yoy have good luck. They some problem's with counterfeit and that one big group sale or that character took off with a lot of people's money and some of them have balance issues way back when but they are a big cell ah wise and ez to connect. I if I want a 20 on your Auerbach I get 20mp ourselves Les connections. Easier to monitor