Need a bit of help understanding a circuit.....
Gadgetman
Posts: 2,436
I have a battery pack...
36V/10AH Li-ion with a built-in protection circuit of some sort...
It's for the electric conversion kit for my bicycle.
(250W motor in the rear wheel, 'pedal assist' system, so completely legal here)
Now, when I began installing the kit, my motor controller went and fried itself(Killed a 75N08 MOSFET. Already ordered replacements from Digikey). As it was my fault, I didn't pester the seller for parts, but I did keep him updated and explained how to fault-find the same problem(he's a cyclist, not a nerd, and it seems he's had 'a few' controllers returned as 'Dead On Arrival', which he now hopes to be able to fix.)
Still no problem...
But he asked me if I could fix battery packs...
The Chinese manufaturer isn't interested in handing out repair instructions, or selling components.
(Warranty? what's that?)
Long story short, I opened up my battery pack hoping to find something I would recognise, but...
There's a PCB, about 2 x 5", 4 TO220 components that has been blanked out, and a whole row of 4pin SMTs.
One SMT for each cell in the battery pack...
They seems to be marked:
817C
which seems to be an Optocoupler.
Except, I can't find any schematic for any charger or protection circuit that uses an optocoupler for each battery cell?
(Trying to google just ends up at some 'datasheetarchive' which gives me a .PDF with no bearing on my question)
Does anyone have a clue as to how it works?
I don't have a picture as my camera is missing in action right now.
36V/10AH Li-ion with a built-in protection circuit of some sort...
It's for the electric conversion kit for my bicycle.
(250W motor in the rear wheel, 'pedal assist' system, so completely legal here)
Now, when I began installing the kit, my motor controller went and fried itself(Killed a 75N08 MOSFET. Already ordered replacements from Digikey). As it was my fault, I didn't pester the seller for parts, but I did keep him updated and explained how to fault-find the same problem(he's a cyclist, not a nerd, and it seems he's had 'a few' controllers returned as 'Dead On Arrival', which he now hopes to be able to fix.)
Still no problem...
But he asked me if I could fix battery packs...
The Chinese manufaturer isn't interested in handing out repair instructions, or selling components.
(Warranty? what's that?)
Long story short, I opened up my battery pack hoping to find something I would recognise, but...
There's a PCB, about 2 x 5", 4 TO220 components that has been blanked out, and a whole row of 4pin SMTs.
One SMT for each cell in the battery pack...
They seems to be marked:
817C
which seems to be an Optocoupler.
Except, I can't find any schematic for any charger or protection circuit that uses an optocoupler for each battery cell?
(Trying to google just ends up at some 'datasheetarchive' which gives me a .PDF with no bearing on my question)
Does anyone have a clue as to how it works?
I don't have a picture as my camera is missing in action right now.
Comments
Here is some info http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
And you can Google 36v Li-ion protection circuit for more links.
found some text 'JZ-YMC-809' on the board, and finally a hit on Alibaba.com but only on the all-chinese part.
At least I found a picture...
http://detail.china.alibaba.com/offerdetail/view_large_pics_1110209072.html
No schematics there, or even a working link to the manufacturer.
(Seems to translate to Manganese Lithium battery protection board)
Since I still can't figure out exactly how this thing works, I'm a bit leery about prodding it with probes when its live, so I can't get a 'OK profile' to compare a dead one to.
Those may not be opto-isolators. They could be MOSfets or BJTs. Obviously there are hazards with probing MOSfets. But seeing as the whole is a banked concept, you might reverse engineer one bank and be able to identify which parts are what by the distribution of power.
If your vendor has dead boards to play with - ask him for one to attempt to rebuild. At least you wouldn't have to worry about not being able to do so. It may be a strictly analog scheme that trickle charges the cell to a limit when there is a certain level of charge. Consider three states of battery charge - full discharge, full charge, and partial charge. Resistor and diode networks would manage all three. If this is only the charging side and the battery has a completely separate output to feed power to the motor - the design is much simpler. It seems each cell is sensed for voltage level separately and maybe there is an overall voltage level sense.
What I'm worried about is possibly finding that this is just some sort of elaborate voltage comparator that shuts off the charger if a cell is 'outside of expected voltage'.
It seems to be listed as a 'Mangansese Lithium battery Protection board' on Alibaba(if Google translates it right).
The board seems to sit parallell to the pack input, too, so I'm not really certain about how it switches off the charging.
I've given the vendor a few pointers on how to find dead cells(where to measure the voltages) and luckily, the packs are flat cells soldered together, not cylindricals that has been welded together.
As the protection board is Chinese and visually looks as if some of the components have been soldered on by unskilled labour, I've also warned him of how to find bad joints.
With that and my suggestions on how to fix the motor controller, I hope that he'll still be selling this stuff when I need to start replacing parts or upgrading in a couple of years...
(Hoping that he gets hold of a controller that supports regenerative braking before then... )
If anyone wonders, there's an actual EU directive for these kind of bikes...
(Electric bicycles were banned in Norway until the EU Directive appeared a couple of years ago)
4 points, really.
1. Max 250W motor.
2. Pedal assist only. No Throttle control.
3. Motor stops assisting at speeds above 25Km/H or if user stops pedalling.
4. At least one brake handle must also cut off the motor power.
One of my uncompleted projects that I designed many years ago, required multiple, rechargable, battery packs. After a little research, I came to the conclusion of building my own battery packs, because it was going to be a huge cost savings. Battery packs should not be complicated, because they are just several batteries wired together to give you the voltage or amperage that you need. I would suggest keeping the battery packs simple, by keeping charging and protection circuitry seperate.
Just my opinion.
Bruce
In this case, though, the pack not only comes assembled in a sturdy aluminium case that slides into a holder on the luggage rack, but it also has a key to lock it in place.(Three positions: Unlocked, locked but off and locked/on)
Just IDed the 4 big TO220 components.
ST Micro STP80N70F4 'StripFET DeepGATE PowerMOSFET'
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00296059.pdf
(N-channel 68 V, 8.2 mΩ, 85 A)
These may be a weak point in the design, so I guess I should look them up on Digi-key or Mouser, just in case.
There is an external Charger for this pack, rated t 42V/1.8A, even marked with 'Li-Ion battery charger'.
As a bit Off-Topic, integrating the charger in the battery of a device means that the device is completely 'tech independent' and can more easily be upgraded. (I have a Psion MC400 laptop from 1989 and an HC110 industrial handheld also from them where the charger is built into the battery pack. I've been thinking of replacing the 2000mAH/7.2V Ni-Cad pack in the laptop with something a bit more modern... You know, to give it more than 20Hours running time)
What does Lithium based have to do with it? Most batteries are capable of starting a fire, under the right circumstances.
However, if you want to keep things in alignment with a current design, now that I can understand.
Bruce
I'm not trying to redesign the system, just trying to figure out enugh of it that it can be repaired if it breaks.
If the vendor I used can fix broken units cheaply instead of having to buy complete new batterypacks or motorcontrollers, his margin goes up, he can lower prices somewhat, his goods sell better, he can buy larger shipments and get even better prices, and so on...
I may even end up doing some of the repair work for him.
(So, I get cheaper upgrades and an occasional extra income... Altruistic? what does that mean?)
If you use the pedals, though, the motor will assist you until you hit 25Km/H(about 15.5Mp/H)
That's fast enough to be a serious contender to my 50cc scooter when going uphill...
The board in that link above certainly looks as if if could be a drop in replacement and better quality.
Since I got started with Parallax, battery chemistry has been a continual project to fathom. Lithium cells have had an interesting development path, but some of the more important facts seem to have been hidden for fear of bad press. The biggest problem of battery charging schemes is that cells in series don't behave well and the longer the series, the more risk of one cell getting out of control. Your board may monitor that and only that. The fact that you have a 42volt 1.8 amp charger indicates that the charge is applied in series to the whole and not to any specific cell in a particular tailored fashion. I don't even know if it is possible to charge individual cells to specific needs if they are all hooked up in series.
But what I do know is that the industry has now moved to individual safety control in each and every cell rather than try to continue with schemes such as what you have. The logic of having each cell monitor its own safety in all aspects is far more failsafe than having a separate board. For instance, lithium cells have to consider several conditions. First, a cell should Never fall below 50% of its rated voltage: second, rates of charge should be slow at first, then move to a rapid charge, and then a top off charge; and third, each cell needs to handle monitoring of overheating of the individual cell. I just don't see how an outside board can do all this well. There is also the need for each cell to provide its own means to manage a build up of excessive pressure by a pressure relief scheme.
I think you see where this is all heading. If you need to rebuild a battery pack - it may be best to use more advanced cells that include individual safety features and discard the monitoring board or locate a better one.
A dead battery pack may have just one bad cell or one bad cell sensing circuit. That is enough to shut out the unit. That is the downside of big high voltage lithium battery packs. If you don't want to service it, there are after market battery rebuilders that do this service - try Nuts and Volts for ads.
It would be very helpful to identify if a rogue cell is the usual battery pack problem or a bad sensing board. If it is the board, a redesign with more robust components would be a win for everyone. If it is a bad cell issue, a different source for cells may be needed.
In any event, it is nice to be able to locate a second source for power if needed.
Also, there is a second link below about Continuous Cell Balancing. This is possibly what the existing board is doing and regardless of its looks, it might do it well.
http://www.batteryspace.com/384v-768vlifepo4batterypacks.aspx
http://www.swe.com/ADMIN/FILES/Lithium Ion Continuous Cell Balancing.pdf
And yes, recharging Lithium-based cells in series is a problem.
The Board listed in an earlier post by Franklin may look like a replacement, but it's for 18560 type cells, and not suitable for the more massive 10AH flat pack cells used in these battery packs.
(I assume there's a reason there's 3 x 85A PowerFET MOSFETs in parallell on the board)
I will try to find a suitable replacement board, though, not just because I'm not too comfortable with the tech, but also because I've been unable to find a source for those MOSFETs...
I'm pretty certain the 817c chips are Optocouplers, and connected to some sort of voltage divider.
Seems like a decent idea to transition from a variable level signal (highest steps are up by 33V or more) down to something that can be combined and used to control the PowerFET MOSFETs.
So, I'll write up a reccommendation, and a detailed fault-finding explanation for those parts I know can be sourced reasonably easily.
I haven't checked the external charger, but I expect it's a constant current type. It also has a Red/Green status LED, so I expect it has some form of monitoring of the voltage or current.
Servicing components on an individual basis is awkward. On the battery cell side - all the cells must be matched for the board to work properly. How does one get one matched replacement cell? On the board component side - you may have to upgrade to newer or more ubiquitous componets, and that takes comprehensively understanding the circuit.
I looked at these Chinese electric bicycles some years ago and at kits to convert an existing bike. The best purchase I could sort out was to buy the kind that has the motor built into a front wheel and do your own conversion, AND to order the battery pack and charger separately from a Western supplier that can sell newer better battery packs as replacements. Buying a whole integrated bicycle of Chinese manufacturer gets you pretty much what is being sold in China - not as good quality control.
Continuous cell leveling is evolving and much of what is being done is NOT available to the public as big companies want to patent or retain as trade secrets there particular successes.
I'll also explain to the vendor that he needs a better board, with levelling support to avoid problems in the future.
The fact that I can't find the ST PowerFET chip for sale in any of the normal sources(Mouser, Digi-key) means there's limited possibilities for repairing broken protection-boards. (I'm assuming that these components are more at risk) As it's listed as 'available' on the ST site I must assume it's mostly sold directly to board manufacturers.
Quality control in China?
I thought the 'QC' stickers they used meant 'Quantity Control'...
The soldering on the MOSFETs (bothh motor controller and te protection board) is horrible, the application of thermal paste was... as if someone threw a couple of gobs of it in the direction of the motor controller...
(I've already written the vendor a warning about that. Hopefully, they have time to check those before shipping more of them to customers. Might save a few from boiling later)
I strongly suspect that batteries MUST be acquired as a matched set unless you have quite a bit of test equipment to assure they are well matched. At may be necessary to have a set from the same production run so that the chemistry is a very near match.
The simple fact is the quality control is far better when the product is specifically made to order for an overseas market. The realities are that many Chinese 'businessmen' jump into something they know next to nothing about and demand that the factory workers get the product out the door. One just does not stay employed by trying to make suggestions that are not cost effective. Also, the general situation is that what you buy is what you are stuck with - returns and refunds are often impossible.
Golden Motor is one of my favorite suppliers http://www.goldenmotor.com/
This should give you some idea of how vast the topic is http://liionbms.com/php/bms_options.php
And BELOW is a book about these circuits.
http://book.liionbms.com/
First off, the board you mentioned is merely a protection board without balancing. Also it is specified for manganese lithium, not the more prevalent LiPO4 chemistry.
The biggest hazard with a simple protection board is that it might just shut down one one bad or weak cell and never allow you to use the battery pack again. On the other hand, balancing boards at least in some cases can either bypass or nurse a weak cell and have the whole battery pack remain useful with as little as 80% capacity. That would mean that two bad cells would not make the battery pack useless, just less output.
So, it seems the best approach is to upgrade to a balancing board in all cases rather than to merely try to swap out a bad cells with a good cell. In other words, a balancing board offers more than protection -- it extends the life of the whole battery pack. But there are questions about the right rate of charge as well.
The other issue here is that you are already stuck with a Manganese Lithium chemistry in a 36V 10amp capacity. So it would seem that you have to buy only a board specific to that chemistry. BUT What I am seeing is 37V 15 amp capacity boards for LiPO4. With some investigation, the LiPO4 may actually be swap-able. Of course, inserting an appropriate 10amp fuse might be wise.
The key here is to get a well documented comparison. Below are links to a Chinese Manganese Lithium Balancing board that would be ideal and has specs, but I suspect the vendor won't sell in small quantities; and the 37V 15amp capacity LiPO4 board.
Both are charging the cells at about 4.25V per cell and both are preventing low voltage operation at about 2.5volts.
Could it be that they are exchangeable? My only concern is that it seems that the 15amp LiPO4 balancing board is willing to charge at rates up to 15amps, whereas your charger is only able to provide 2amps. It seems that the added difference between balancing boards and protection boards is that a faster charge is also available. You might be able to use a 2amp charger with a 15amp board and just wait longer or maybe not. The vendor is listing a 1.3amp charger on the 15amp board's page as an accessory. I suspect the 15amp charge rate may be a typo.
The other implication here is that first mentioned protection board which is intended for small LiPO4 batteries might charge on a 2amp charger at ae slower rate, but be fine for getting your 250w of power out when needed.
Open the pdf and compare the specifications of these two boards below. The first is LiPO4 and can be gotten in the USA, the second is Manganese Lithium and might only be gotten in quantify in China.
http://www.batteryspace.com/pcmwithequilibriumfunctionfor37vli-ionbatterypackat15alimit.aspx
http://www.mafbattery.com/en/productlist.asp?ID=Y16V6W6U0S
Frankly, documentation has its own quality control issues as well. But you definitely don't have balancing of any kind with your set up.
I am beginning to think that a 10 cell Lithium battery management system is an ideal Propeller project. Digital is supposed to be better than analog and as I mentioned above, balancing of discharge might nurse weak or bad cells. Could one bypass these with an SCR?
http://detail.china.alibaba.com/buyer/offerdetail/1110209072.html
I'll also make certain to tell the vendor here about them and that he should seriously consider upgrading the packs with them.
As for the battery chemistry... Frankly, with the Smile the manufaturer has stuffed into the case, I'm not that certain that they even picked a board for th right chemistry...
(The vendor calls them 'Li-ion' packs, but then again, so does anyone if they don't know the difference between the assorted Lithium-based cells)
Topic 2 - Battery Cell Balancing - What to Balance and How.pdf
Most of these manufacturers and vendors don't have English ability appropriate for translation of highly technical material. So documents end up with typos, misnomers, or just saying what they think the customer wants to here. Golden Wheel has a comparision of LiFe04 and LiMg batteries that is not very favorable. It appears that one should avoid temperatures over 50 degrees centigrade to preserve long life. It would be ideal to have all ten cells monitored for over-heating. Even one sensor that shuts off the AC mains to the charger when 45 degrees centigrade is reached may extend battery life quite a bit. This kind of approach could be done with something as simple as a BasicStamp or a DallasSemiconductor thermostate chip which is attached to a solid-state relay.
Here are two interesting files to read. One is about balancing and the other is a chip that is NO longer available, but ideal.
I continue to read and I find that NOT all balancing is good balancing. Also, it is easier to balance charge as it is a lower current than discharge.
Also, a significant issue is that cells in the same production run can vary by about 15% in their characteristics.
The main thing is that all the boards that have been referred to are okay for electric bike use even though the documentation is somewhat hit and miss. Your 250watt limit actually means that you can use a cheaper board as it is not uncommon for these 10 cell bike batteries and boards to provide power to a 1000watt motor. A 15amp rated discharge is quite adequate. Those 3 parallel power FETs that you are concerned about are for a peak discharge spike, but the board is rated for a mere 15amp steady discharge. I am not sure why you think opto-isolators are required. For balancing, 8 smaller power FETS are usually used that do look like opto-isolators.
I am becoming more and more intrigued by the idea to have a Propeller provide a custom board. One might even be able to have a small database to profile the charge and discharge of each of the 10 cells. It seems that physically matching perfectly is rather impossible, but profiled charge and discharge of 10 cells is possible.
Hello again, I cannot seem to stop thinking about making a better board for these. So I have written down my design thesis so far. Please excuse the typos. I will revise and resubmit later.
This could be a lot of fun and enable many users here to play with bigger and better motors. I believe Golden Motors has 2-8 Kilowatt 3 phase brushless DC motors that operate from Lithium cell packs and are very adaptable to robotics projects. These are ready for chain drive and speed control. And all these motors depend of multiple cell Lithium power packs. So a good DIY Battery Management System would be very handy.
(The site is bookmarked for future projects... Especially interested in the motors suited for scooters... )
It's not a very good idea to use those in bikes, though.
A 500W motor 'kicking in' a bit hard can wreck aluminium front forks on a bike, and even older steel forks.
(Not certain what it'll do if it's rear-wheel mounted on an aluminium frame)
Then there's legislation.
In the EU and countries that adopt EU regulations, 250W is the max allowed.
Going beyond the regulations means you suddenly have an unregistered, non-type approved motorized vehicle.
And yes, in many countries, that kind of law covers all roads, not just those open to public.
Lithium Battery Board Design for e-bikes (corrected).pdf
Some of the boards mentioned have more than 10 cell capacity. The pdf for the Dallas Systems chip shows how to wire the sensor wires if less cells are to be used. So a 15 cell board can be easily adapted to a 10 cell board.
Regarding large, high power brushless motors - they don't have to be used in vehicles. One might need a battery operated table saw with solar recharging or a battery operated sewing machine. In some cases, large ventilation fans might be employed without being on the grip or water pumps.
3-phase generation of electricity is even possible and it can be converted to DC to charge batteries.
BTW - Golden Motor advertises 36V/10amp LiFePO4 battery packs which may really be LiMO. And all their battery packs may be suspect as they seem based on a 3.6 volt cell.
True LiFePO4 provide 3.2-3.3 volts per cell, while the LiMO provide 3.6-3.7 volts per cell. Ask how many cells in the pack to verify chemistry.
And I wouldn't worry too much that the construction looks as if it was built in 1960s. Generally, if it survives the first few months - it will give a good service life.
I do not see anything difficulty about repairing motor controllers, but there are endless problems with repairing battery protection boards or battery packs.