Making a battery pack

[Fuzzy Head]

Hello everybody.

I have one of these:
http://www.google.co.uk/search?hl=en&q=pdq+power+trike&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.41524429,d.d2k&biw=1280&bih=868&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=xFoFUfPWFYGV0QX71IGYCQ
Fundamentally it is a wheelchair with an attachment for the front part of a BMX bike with a hub motor. From a Design/Engineering point of view it is quite an interesting machine and although quite old now it is very helpful in allowing me to get around until I fully recover, it also suited my needs better than anything else I could find at the time of purchase. Currently it has lead acid batteries which weigh a tonne and don't offer much range (partly due to what I think is called the Peukert Effect). Seeing as I have a strong interest in how things work I have decided to build a battery pack rather than buying a pre built one.

I believe the motor is a 150w DC brushed, direct drive, hub motor that it designed to run from 36v. Although not very powerful, if this project goes well I intend to upgrade the motor and control box.

I would like to start by making a smaller battery pack with the intention of it being a backup battery pack in case the first fails which will be put under the seat. Although the Trike is much like an ebike I can not just cycle the rest of the way if something goes wrong or run out of power, so I need to make sure I get quality reliable parts.

Although I have done a good amount of research I am no expert with no practical experience with LIFePo4's (the chemistry my research has lead me to believe is the best choice with current technology) therefore I am seeking advise before I make a purchase and assemble the thing.

Some possible part choices:
http://www.bmsbattery.com/lifepo4-cell/118-headway-38120s-lifepo4-battery-cell.html x12
http://www.bmsbattery.com/bmspcm/322-17s26s-24a-max-discharge-current-bms.html
http://www.bmsbattery.com/alloy-shell/25-alloy-shell-240w-lifepo4li-ionlead-acid-battery-ebike-charger.html

Has anybody had any experiences with the company BMSbattery? I am not sure what sites are best for parts. I live in England. The above site has an option for GBP but the price estimates seem vague.

What do you think of my part selection? Take into consideration that these parts must be very reliable and I can not risk them bursting into flames.

Would it be worth my while getting a BMS with a much higher discharge current capability than I am likely to ever need?

Is the charger I selected appropriate? It is about 0.5c I would rather extend cycle life than reduce charge times.

Apart from battery connectors what other parts will I likely need that I may have overlooked?

Thank you

 

[Fuzzy Head]

I have just found this topic: http://endless-sphere.com/forums/viewtopic.php?f=14&t=38284

I am a bit embarrassed I did not find it sooner but there are so many topics.

I will read into it in more detail tomorrow and it does put a big question mark over BMSbattery. Still I always like the topics involving taking something apart to find out what is going on.

 

[dnmun]

why not just buy a pack from ping already built? or from sun-thing guy? you should not need a bigger BMS than what is on the battery.

 

[dogman dan]

Likely a typical signalab bms, like pingbattery uses, would give you plenty of power for your future needs. I pull 1200w from them all the time.

Lots of options for batteries, but a lifepo4 pack with a bms would be my recomendation. Easy to maintain and safe to charge nearly anywhere. If you want to save some trouble, and have the money, get a 36v 20 ah pingbattery, or a similar pack from other vendors. Then you can completely ditch the lead, and have amazingly more range.

The lowest cost per mile battery I have owned, was a 36v 20 ah lifepo4 pingbattery.

You might also look into smaller 9-10 ah limn batteries. One of those would give you ability to use 600w later easy, and get you lots of range as well.

How's the budget? Is it super tight like it is for nearly all of us? Or do you have $500 to spend?

BMS battery is not at the top of our recomended dealers list. Grin cyclery, and Pingbattery are.

 

[Fuzzy Head]

Thank you for your replies

I know it would be easier and most likely cheaper to purchase a ready made one but the fact is that I am currently really getting into subjects like physics and chemistry and hope to study an area of science at UNI ,haven't decided exactly what yet. This is mostly because whenever I look at something I desire to know how and why it works. This is why I wish to build the pack myself, it is not just a practical item but a project and a learning experience. Seeing as we are currently doing a lot of lab practical work I am hope that that will help with this as well as this improving my abilities and scientific practice.

Budget it about £200 (not sure what exchange rates are) for everything I will need to buy

The Grin Cyclery looks very good for some things but I have yet to spot individual cells or a BMS.

What about well known UK based sellers of parts? I am hoping to avoid shipping costs, maybe there is not enough demand here for such companies to buy in bulk.

When buying Cells and BMS what are deemed the best brands to go for?

Thank you

 

[SamTexas]

This is mostly because whenever I look at something I desire to know how and why it works. This is why I wish to build the pack myself, it is not just a practical item but a project and a learning experience. Seeing as we are currently doing a lot of lab practical work I am hope that that will help with this as well as this improving my abilities and scientific practice.

Ambition is good. Enough to build a battery pack from scratch and for practically nothing? Look into recycled laptop batteries. There are thousands of them being thrown away every day in every major city in the world. Once you sucessfully build a good usable pack, you might no longer give BMSs another thought. Around here to some of us, BMS stands for Battery Murdering Systems. And that's being nice. I use another term for them, but it's not fit for print. Obviously many other members use BMSs. There is even a fool who claimed that LiFePO4 can only be balanced by a BMS, that without a BMS LiFePO4 cannot be used!!!

 

[dnmun]

You have already talked two people into damaging their batteries with your idiotic suggestions. why don't you guarantee that if he builds a lifepo4 pack from scratch that he will never damage it from overdischarge or overcharging. just put your money up front so he can buy replacement cells when they are ruined like you did to milou and the other guy. you are so ignorant of how a BMS works you act like they are useless. or even better tell him he can build a battery from laptop lipo packs. when you give people bad advice you should take responsibility for it.

 

[dogman dan]

Much difference of opinions about bms's. I just say don't trust them blindly. I run both bms equipped batteries and non bms equipped batteries myself. Or perhaps I should say, I am the human bms when I don't use an automatic one. You bet I've ruined a few batteries running bareback. When using a bms, I still pay attention to my voltage and capacity monitors.

Your budget is small I think, for a large pingbattery. But I'm not familair with prices in pounds. That makes a scavenged laptop cells pack attractive. You want to learn, so nothing makes you learn like ruining some stuff. But if you go that route, it will be quite a bit of work.

RC lipo (lico chemistry) from hobby king can be an affordable way to have lots of power from a very small pack. Just don't learn about lipo the hard way. I'm assuming that if you wake up and the house is on fire, it would be a big big problem for you. You might consider HK's lifepo4 packs.

With a bigger budget, I'd tend to suggest the A123 20 ah pouch cells that are currently avaliable. Your budget might be very very tight even for the headway 10 ah lifepo4 cells.

You got lots of reading to do bro. Enjoy!

 

[999zip999]

I love the idea of cut a front half of a bike up and bolt to a wheel chair great.

 

[SamTexas]

Why don't you guarantee that if he builds a lifepo4 pack from scratch that he will never damage it from overdischarge or overcharging.

Only an idiot would guarantee something like that. So I'll let you have that honor and guarantee him that his battery will never fail with a BMS.

...just put your money up front so he can buy replacement cells when they are ruined like you did to milou and the other guy.

I did that? Great! Hey Milou and the other guy, are you still here? Please come in and confirm.

you are so ignorant of how a BMS works you act like they are useless. or even better tell him he can build a battery from laptop lipo packs. when you give people bad advice you should take responsibility for it.

I'm positive they are useless for me. Just as I'm positive that you are a pretentious guy, going around looking for new, inexperienced members to tell them to disassemble their chargers while the problem lies elsewhere. To expect them to thank you for every idiotic advice you give. To impress them with your knowledge about LaPlace transform. You, a retired scientist from HP? I know technicians who know more than you.

Here are just a few claims you made, just off the top of my head:
LiFePO4 must be balanced by a BMS. Cannot use LiFePO4 without a BMS.
The LiFePO4 BMS is working when one more cell has gone pass 4.0V
A 72V battery will not make an ebike go any faster than a 36V battery.
A 48V LiFePO4 battery MUST have 16 cells in series. 15 is not possible.
All BMS must take power from the first 4 cells. 3 cells is not ok.

You can have the last word. I'm done wasting my time with you. I'll let other members save the poor newbies from your foolishness.

 

[Fuzzy Head]

It appears as though this topic has brought up some arguments. Hmmmm

I have seen a few examples of people who have made packs from old laptop cells and although a novel idea with some merit I would imagine that keeping such a pack balanced and in good condition would be difficult as every cell would have a different capacity and the likely hood of one failing in the series parallel arrangement would be high. The main reason I decided not to go down this path for this battery pack was that normally when a laptop battery is discarded it has very little ability to hold a charge remaining, not to mention a lot of soldering.

For this first project I will go for new cells.

Correct me if I am wrong. With chemistries such as LiPo, Li-ion and LiFePo4 due to their chemistry over discharging them (bringing their voltage/emf below a certain amount) can cause them to become unstable, loose capacity and potentially explode? The same sort of damage can occurs if overcharged (their voltage/emf goes above a certain amount), I think the odds of explosion are greater. And the purpose of a BMS (Battery Management System) is to shut down the pack if an individual cell reduces below a certain voltage during discharge. Or in the cause of charging prevent the voltage of an individual cell to exceed a certain amount. I am as of yet not sure mechanically how the cells are balanced by a BMS but I suspect something like a comparator detecting voltage (no expert at electronics yet) and when this happens it essentially puts that cell in parallel with a resistor so it receives less current.

If the above is correct and seeing as form my experience with Lead acid batteries over time as cells age and decay they are charged as slightly different rates resulting in different terminal voltages. I do not see why it would be advisable for most people to not use a BMS. I also do not see how they would cause damage through normal operations. Please explain?

Does anyone know of a good place I can find detailed explanations of how a BMS does what it does?

I do, however, agree that a BMS can not be blindly trusted, it is after all just a machine and in some cases poorly designed ones with substandard parts. At first I will be checking the cells regularly with my multimeter.

The main reason I favour the idea of using LiFePo4 to be used regularly is the high number of cycles, over 4 times that of LiPo which makes them cheaper in the long run. And from what I have read they are also better suited for high C (capacity) discharges and have a naturally far more stable chemistry than LiPo, particularly when something goes wrong. As much as I would like to see some batteries go up in flames I really don't want it to happen when I am least expecting it.

In GBP prior to delivery costs the selection I asked about in my first post of 12cells, charger and BMS would have costed me about £133 which doesn't seem too bad. After reading the charger topic I will avoid their poor excuses for chargers. Is there any way of knowing if the headway cells being sold by BMSbattery are of a good standard?

The A123 20 ah pouch cells do look good and they do take far less space. It is odd that they want my details for me to access the datasheet though.

999zip999 it is a shame the PDQ power trike is no longer available new. Apparently the early models of these trike's had a lot of problems. The biggest one was an appallingly designed control box that overheated burning out the transistors. The early control boxes had a tiny heat sink with a fan on it in a small sealed plastic box. Oh and people deciding to race them and tipping them over on a sharp bend.

 

[dogman dan]

Some RC lipo has crazy high c rates. like 50c or more. But not the laptop cells.

The headway cells should do the trick for you, and you could get 1000 real world cycles. If 10 ah is not enough capacity, they will still extend your range nicely when used in addition to your existing lead pack.

I'm not familiar with the exchange rates, so I thought even those might be too pricy for you. To protect yourself against the possibility of recieving a bad cell, it would be prudent to buy 13 cells, so you have one spare just in case you have a problem with a poorly made cell.

A signalab bms and matching 5amp charger from pingbattery.com might be a good way to go. As reliable as any bms I know of, though I don't know much. I just have gotten years of reliable use from mine. One nice feature of the current model is that it had a light that indicates when each cell is full. So you can at least tell when it's fully charged AND balanced.

Lastly, a voltmeter or better still a votmeter /wattmeter, will help you know if the battery is actually full, and how much you might have left.

If the budget makes you go bare bones cheap, sans bms, then you could build your pack so that cellog8 voltage monitors could be used to give you a readout of each cells voltage. The pack could be charged by building it in two 6s sections, and charge one section at a time with an inexpensive, but very slow Imax B6 RC charger. The balancing feature of the bms is built into these chargers, so you'd at least still have that. Then with experience, simply do not go far enough to overdischarge.

Have fun!

 

[docnjoj]

I have just found this topic: http://endless-sphere.com/forums/viewtopic.php?f=14&t=38284

I am a bit embarrassed I did not find it sooner but there are so many topics.

I will read into it in more detail tomorrow and it does put a big question mark over BMSbattery. Still I always like the topics involving taking something apart to find out what is going on.

Here is some A123 AMP 20 data.
http://www.endrich.com.tw/html/ezcatfiles/i-web17/img/img/25755/A123_AMP20.pdf

otherDoc

 

[Fuzzy Head]

I joined BMSbattery and I thought they were cheaper right until I saw the delivery cost for the cells. It was the same as the cost of the cells. As a result I will not be buying from them but I did find this website: http://eclipsebikes.com/headway-lifepo4-38120s-10ah-p-1011.html The items are more expensive though it seems to be made up for by lower delivery costs as they are based in the UK. When I did a quick check it was not too much higher than £10 for delivery. Hopefully they will turn out to be a good seller. They also sell chargers and BMSs.

Their chargers seem to be good but the voltage is right on the upper limit, I may be able to adjust the voltage or use a single diode to drop the voltage slightly. 43.8/12=3.65v per cell. http://eclipsebikes.com/lifepo4-battery-charger-p-1037.html

The signalab bms does look good I have read about them but can not find anywhere that has the model with the lights in stock. Maybe it is my poor shopping skills. *hates shopping*

The cellog8 looks like exactly what I am looking for, it is a shame they don't make a cellog12 with 12 readings.

I will have a half term holiday in less than 2 weeks, I will order everything so it arrived then.

Thank you everybody for your help

 

[dogman dan]

Just build your pack with two 6s jst balance plugs, and then you can use two cellogs, or just move it back and forth to each plug. The cellog will simply read 6 cells then.

You might have to actually Email Li Ping at pingbattery to buy a bms. He sells parts, but it isn't his main buisness.