GoldenMotor.com Forum
General Category => General Discussions => Topic started by: Abe on August 30, 2015, 06:42:26 PM
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Hello Alan,
1. There is a population that chooses not to use the BMS controller, if so, what is the advantage or disadvantage that BMS controller used?
2. How can I check whether the BMS controller, ie check whether work functionally controller completely normal.
3. The recent past you indicated that you are not working with controller, why?
Thank you,
Abe
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Most commercially available battery packs come with built in Battery Management Systems (BMS) which is used to monitor the voltage and more importantly protect the individual cells from being either overcharged or overdischarged, and the BMS circuit board will probably look something like this:
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=3031.0;attach=4237;image)
Lithium cells are very sensitive to overcharging, and Lithium Polymer (LiPo) cells in particular have been can suffer from thermal runaway which can cause the battery to suddenly burst into flames if it significantly overcharged above the maximum safe voltage for too long.
Lead Acid batteries would overheat and boil the electrolyte if severely overcharged, but would not burst into flames.
Lithium cells do not like being discharged too low either, and if this happens, it can permanently damage the cells making them very unstable and unsafe to use.
The BMS within the battery is designed to stop this from happening by preventing further current from passing if any of the battery's cells are above or below the pre-set operating voltage range.
The disadvantage of having a BMS is more space is required, more weight has to be carried, there are more wires and connections, and it's more complicated and more expensive, but the safety advantage of using a BMS is much more important when you consider that the typical eBike user will probably know very little about battery safety and the possible dangers involved with not using a BMS.
Unfortunately, without dismantling your battery and checking each of the cell voltages with a voltmeter during the charging and discharging process you will not be able to tell if your battery's BMS is actually working correctly or not. ::)
I don't use a BMS with my home made LiPo packs because I have been using Lithium batteries with radio controlled models for years and have always used balanced chargers which actually monitor the individual cells while charging:
(http://www.arhservices.co.uk/GoldenMotor/Charging.JPG)
I used to use a very basic battery monitor to check the pack voltage which had an audible alarm that would sound if the pack voltage dropped below a pre-set voltage:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/Batterypack.JPG)
But this wouldn't notice if a single cell was weak and dropping more than the others, so I now use a different battery monitor unit that checks the voltages of each of the individual cells:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/2015-08-30%2023.57.20_zps0woqzagv.JPG)
I don't use a dedicated BMS unit because my battery packs are very basic, small and lightweight, and I always use a balance charger and never leave them unattended while charging, so I have saved the additional expense and complication of having a dedicated BMS unit wired permanently into each of my home made battery packs.
(http://www.arhservices.co.uk/GoldenMotor/P7021933_zps9efa95f6.JPG)
The larger frame bag on the right holds two 7S 5Ah packs which I can either connect in parallel to produce a 25.9V 7S2P 10Ah pack, or in series to create a 51.8V 14S1P 5Ah pack:
(http://www.arhservices.co.uk/GoldenMotor/Smart%20Pie/AfterLH.JPG)
The smaller frame bag holds two Turnigy 4S 5Ah hard case packs (https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=15521) connected in series to give a 29.6V 8S1P pack:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/Batteryarrangement_zpsc145338d.JPG)
As well as the two batteries, a fuse, battery connectors, balance lead adapter and the battery monitor unit, there is still enough room inside the bag for two Turnigy Watt Meters, a lightweight dog lead and an emergency supply of poo bags. ;)
Alan
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Thank you so much
Abe
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hi Bike Mad..
i wonder if regen have good impact to your batteries.. ?
i mean how regen work to charge batteries with or without BMS..
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The Turnigy batteries I use on my home made packs are rated at a 5C charge rate which means that even the small 5Ah pack can accept 25 Amps continuous charge and my maximum measured regen current was 23.35 Amps (681.5 Watts) using a 7 cell LiPo pack (25.9V 10Ah) and 9.65 Amps (525.8 Watts) using 14 cell LiPo pack (51.8V 5Ah).
I have also checked for excessive cell voltage during regen using a CellLog 8S to monitor and record the battery and cell voltages during a trip:
(http://www.icharger.co.nz/product_pic/celllog8s_e.jpg)
On the numerous test rides I have carried out I have not had any of the cell voltages rise high enough to trigger the over-voltage alarm, even on steep hills:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/CellLog%208%20graph_zpshjh9n0rb.JPG)
The above graph relates to just the first ~3.6 miles of the return trip shown below showing the elevation in feet and distance in miles:
(http://www.arhservices.co.uk/GoldenMotor/Returntrip.JPG)
You should be able to tell from the above elevation chart that there were some reasonably steep hills on this trip.
I have not been able to test the maximum charging current and voltage that regen is able to deliver to a BMS equipped battery through the power outlet connection.
It would be nice to know whether the BMS would actually prevent excessively high current and/or voltage from reaching the battery when the motor is producing regenerative energy on a very long steep hill.
With the MP4 and MP5, if the Overvoltage protection value is set correctly on the controller settings then I would expect the controller to cut regen power if the set voltage was likely to be exceeded.
Alan
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thank you Alan for this info.. :)
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Alan,
You mentioned that currently now you are using a device with an audible alarm that connects to each cell & monitors for low voltage...
1st- Does it monitor for high voltage also or only low voltage?
2nd- Can you custom set the ranges to whatever you want it to alert to?
3rd- I'm assuming though it monitors each cell, you don't have 1 device per cell, so how many cells can you connect to it at any given time?
4th- How do you know which cell its alerting to?
5th- Does it monitor in real time or periodically check it or just sit idle until the low mark is hit?
6th- Finally what's the name of it, where do you get it & how much did it cost?
I guess that's enough questions for the time being... I await your learned reply;) thanks again, I always learn so much reading your posts...
Adam
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Hi Adam
It's called CellLog 8 and can monitor up to a maximum of 8 cells or just the total battery voltage and has an alert for both high and low voltage limits:
(http://www.hobbyking.com/hobbyking/store/catalog/CellLog-8M.jpg) (http://www.hobbyking.com/hobbyking/store/__10952__Cell_Log_8M_Cell_Voltage_Monitor_2S_8S_Lipo.html)
The trigger voltages can be adjusted to suit different cell types and it clearly indicates which of the cells has triggered the alert.
Check out this post (http://goldenmotor.com/SMF/index.php?topic=3057.msg18348#msg18348) for more details.
Unfortunately HobbyKing only have the CellLog 8M and no longer sell the more useful CellLog 8S version which has data-logging capabilities and a usb connection for downloading to a PC.
Alan
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1st- Sounds like I should look around to see if I can find this "CellLog 8s"?
2nd- Or is it made by "Hobby King" so I won't find it elsewhere & just need to be content with CellLog 8m"?
(2nd answer) I did some googling & for those who still want the 8s instead of the 8m, other stores sell them at about twice the cost of the 8m. $17-8m /$34-8s.
3rd- Can I use say 1 CellLog 8s on say a 8S3P battery such that each log line runs 1 in series & 3 in parallel? Or is that a no-no? Will it be able to tell that 1 of the cells isn't right & alarm if the other 2 are fine?
4th- I found a post on ES that claims that this device is very problematic with unbalancing the cells... Apparently, line 1 powers the device & 2-7 are just monitoring lines...
5th- The other complaint is that it can over-discharge the cell if left in place when not in use... But putting switches in line (requires 8 switches) compromises the monitoring ability & removing it comprises the durability/lifespan...
So confusing...
Adam
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Hi Alan..
have you try to overvoltage the Magic Pie to 63.4V with 5 11.1V Lipo bateries?
id notice that the Lipo will a bit "big" like there is air inside it..
if yes.. how you make the Lipo "slim" again just like new?
regards
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I did once try a 15S LiPo pack just to find out if the controller would actually run on 63V but only for a quick test as I did not want to risk further damage to the controller capacitors which are rated at 63V max!
If your LiPo packs are beginning to bulge (baloon up) they have probably been overcharged, overloaded, or overdischarged at some stage, and it is not recommended to continue using LiPo packs in this condition as they are no longer considered safe to use. :(
(http://www.arhservices.co.uk/GoldenMotor/LiPo/2014-12-08233706_zps3f6131d2.JPG)
(http://www.arhservices.co.uk/GoldenMotor/LiPo/2014-12-08233449_zps09cf0203.JPG)
(http://www.arhservices.co.uk/GoldenMotor/LiPo/2014-12-09000555_zps85191b17.JPG)
(http://www.arhservices.co.uk/GoldenMotor/LiPo/2014-12-09171416_zpsf4ae226a.JPG)
Unfortunately, the individual cells tend to become quite unbalanced when this occurs and the weaker ones can easily become overcharged and further damaged:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/imballanced%20cells_zpspajkxpvm.JPG)
Although I have previously tried making a small hole in each of the cells and resealing them after the excess gas has been squeezed out, it has not been very successful in the long term and this process can be very dangerous to attempt due to the high risk of the cells exploding when punctured (https://www.youtube.com/watch?v=gz3hCqjk4yc&feature=youtu.be&list=WL&t=41).
Alan
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thank you Alan for this info.. well Golden Motor should change the Golden Meter app overvoltage setting to only 63V instead right now 65V..
thats make me want to try... haha
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Alan,
what if I do set MP voltage to 36v & use 50.4v (4 LiPo)... does this effect the controller?
have you try this?
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If you are planning on using a battery pack comprising of 4 x 3S LiPo packs connected in series (4x3S = 12S = 44.4V nominal 50.4V max) with the controller on the 36V setting, I would suggest lowering the Overvoltage protection value (V) from 52V to 51V and raise the Undervoltage protection value (V) from 31V to 36V.
The 51V setting would be high enough to allow the controller to work correctly (even with a very slightly overcharged pack reading between 50.4V~51V) whilst it should also prevent any serious overcharging if regen is used with an already fully charged pack, and the 36V Undervoltage protection value (V) setting will prevent the LiPo cells from being discharged below 3V per cell.
The alternative option would be to use the 48V setting with the Undervoltage protection value (V) set to 36V, but on the 48V setting you cannot reduce the Overvoltage protection value (V) below 61V.
This means that you will need to ensure that regen is not used straight away with an already fully charged pack to prevent overcharging the battery, and the 36V Undervoltage protection value (V) setting should prevent the LiPo cells from being discharged below 3V per cell.
I think you may also find that the regenerative braking will work more consistently using the 48V setting with a 44.4V pack than it would using the 36V setting with a 44.4V pack.
Alan
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thank you very mich Alan for this info.. :)
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I try to keep my LiPo packs as simple as possible with high capacity cells such as 4S 20A and 6S 20A packs. When my packs come off at 62V fresh off the charger (4S @ 3.9V/cell), the regen does not work as over voltage protection is set at 63V since it will not even run with the default setting.
(2) 4S + 6S packs gives me 14S 20A which has been a great voltage to run the MP5 at. I usually set the under voltage alarm via cheaper cell alarms ($4/ea) that have a simple LED and pretty loud alarm allowing one to set the alarm at the cell voltage they want. I like the Cell Log as it can do a lot more and even handle 8S packs, but I only have one.
I also use an RC balance charger to reset and condition my packs to be in good health. I have put serial numbers on each pack and created a small database to log each use. In addition, I often carry a bulk 6A 14S charger for lithium ion/poly batteries as its small and effective for getting my pack up to around 57.4V. These batteries are rated to charge up to 4.2V/cell, but for each 0.1V you lower at charge, it doubles the cycle life of the battery. Of course there is a point where the battery serves no utility, but I tend to charge from 3.9 to 4.1V/cell depending on what my immediate needs are.
Why no BMS? I don't like to charge to the maximum voltage per cell. I like to be able to monitor each cell--they don't get out of balance as long as I don't overdischarge them. I have had previous experience with a FEW battery packs where the BMS failed or did not perform to my liking (cells not balanced actively, discharge rate too low). I have even been stranded due to a overheated BMS in lockout mode. My laptop batteries that have failed often revealed mostly a good battery with a single bad cell.
I still have two packs with newer 18650 cells that have a BMS. I allow friends and family members to use them as they are simple to use (until they catch fire).