GoldenMotor.com Forum
General Category => Magic Pie & Smart Pie Discussions => Topic started by: Thuktun on June 02, 2016, 05:47:30 PM
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I have a question about over voltage and regenerative braking. I'm building a 14s battery so fully charged will be 58.8v. when I brake and the voltage goes above the allowed 63v what happens?
Does the controller fry? Does the regenerative braking suddenly cut out, dropping the voltage, then cut in and continue cutting in and out as the voltage rises and falls? Does it apply only enough braking force to keep the voltage at 63v?
Is it better to just turn it off?
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Hi Thuktun
you have to differ between the Storage side (LiIon) and the electronic side.
The Battery when fully charged is easy to overload which leads to a fast decay of their capacity. LiPo starts to drop metallic Lithium on the cathode (which is a very active metal!!!) when overcharged and typical burn off instantly. I never had LiMn for testing (I used one from Sony) but I guess they loose capacity quite fast. A BMS generally acts when overcharged with seperating the charger (Regen) from the battery itselfs which forces the BLDC controller to waste the generated energy in it FETs which works quite OK as long as the energy is below the thermal load it could dissipate.
The controller is build for 48V blocks (12S typ) and when reached 63V a) the condensators might blow (especially when they get older and dry out) or b) the FETs are overstressed and fail (continues ON or off).
Regen braking is very functional and I love it enormously (if it would work in my controller yet) as I had in the past, but the Energy saved in a typical situation is only a few percent on a normal (not too hilly) ride. I did a Matlab simulation four years ago on my typ. daily ride with about 10 traffic lights I surely have to stop a few bridges and the about 40m altitude difference and the 23km single distance ride. I later compared it to my (onboard computer) datas in the Battery and it was (sadly) a 2-3% energy conservation instead of wasting the energy in the brakes.
Cheers
Sam
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Okay, but that didn't answer what I asked lol.
I just want to know what happens to the controller and how the feature behaves, I know what can happen to the battery if over charged. I know I don't get any usable return in energy, but I do get extra stopping power which is always a good thing.
Thank you though. :)
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Hi Thuktun
it's exactly as I've written:
the BMS will cut off the connect which means the Controller have to burn the energy and therefor gets hot until it's damaged. This could happen on the first try or work for years. The controller itself has no protection build into against misuse or overvoltage, while it features an overcurrent protection (current limitation) for the engine, unluckily not on the 5V line. Nice features like wrong polarity protection, overtemp. protection, Overvoltage shutdown, RPM Limits where never integrated (maybe in the newer MP5 as I haven't had one yet, but the MP3 and MP4 controller does not feature such "fancy stuff". The same goes for the low voltage level the MP series allow by design.
Alan could surely say more about the usecase, as I see only the electronic/construction side.
Cheers
Sam
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Hi Sam.
I want to start out by saying I'm sorry for hurting your feelings. I'm just a bad tempered evil old geezer who clearly hates all form of life, and disagrees with everything said by anyone. So please don't ask to get me kicked off the board. Again.
Whoever explained regen to you had no idea how a generator/battery set works. Find a different source.
Hi Thunkun
It is not good engineering practice to subject components , particularly electrolytic capacitors, to voltages near their rated values. If your circuit is using 63VDC rated caps, I suggest you build a lower voltage battery set as a power source. Regen is a current producing event. The output voltage is a result of that current, mutliplied by the impedance of whatever circuit is connected to the generating coil. (I x R=V) An open circuit or very high resistance circuit will cause a very high voltage to be developed to make that current flow, while a very low resistance circuit will cause a very low voltage to be developed. (I x R=V) Using a 58VDC battery set will result in a regen voltage close to 58VDC, while using a 50VDC battery set will keep the regen voltage closer to 50VDC. Since you are building your own battery set, you can pick the voltage….
I personally do not like the variable effect regen has on braking performance.
Again, Sam, I apologize for being such a terrible person. Please don't hate me.
TTFN,
Dennis
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Hi Thunkun
It is not good engineering practice to subject components , particularly electrolytic capacitors, to voltages near their rated values. If your circuit is using 63VDC rated caps, I suggest you build a lower voltage battery set as a power source. Regen is a current producing event.
Dennis, the battery he is building is similar in voltage to your GM 48V LiFePO4 battery.
Your battery is 51.2V nominal and 58.4 fully charged, whereas Thunkun's will be 51.8V nominal and 58.8V fully charged, so the 0.6V difference in the nominal voltage and the 0.4V difference in the fully charged voltage is nothing to worry about.
The following was observed on my original Magic Pie:
If you disconnect the battery and pedal fast enough (with brake lever pulled in so that the regen is on) the generated voltage being output does not go above ~60V which is fine, however, if you do not apply the brakes, the voltage continues to rise well above this level.
By winding the pedals as fast as I could by hand, I made the wheel spin pretty fast. I looked at the voltmeter and observed a reading of ~77V , so I immediately grabbed the brake because I was worried about damaging the controller with such a high voltage going through it.
With the battery connected, this excessive voltage rise should not occur, as the residual current being generated while regenerative braking is not activated should be easily absorbed by the battery.
We have recently enhanced the cruise controller to detect if the battery pack is in place. If the battery is switched off, or is not connected at all, the controller will check the back EMF voltage, if it exceeds the preset limit, the controller will disable the regenerative braking to protect controller from being damaged.
As of today, 22/7/2009, the day of the eclipse, all GoldenMotor controllers have a new function to deal with the issue of regen braking burning out the controller while battery is off.
Unfortunately, I have not tried the same high speed hand pedalling test on the later Vector controllers to see if they work the same.
It would be interesting to find out what happens to the controller's voltage if the battery's BMS isolates the battery from the controller during high speed regen.
Alan
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Hi Alan
To be honest, I never even considered that someone would disconnect the battery from a motor they were using! Open circuit regen voltage could be just about anything.
I agree with your comment about 0.4 VDC battery constuction difference being nothing to worry about. My concern was using 58VDC supply voltage if you know you have caps that are rated at 63VDC . It just isn't a good idea. I believe GM management learned from the "48Volt" MP3 disaster, and have uprated the cap rated voltage on current production product.
At any rate, my external controller is still working just fine:)
TTFN,
Dennis
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Okay, so it won't hurt my controller, that's good and as I expected. But I still don't know how the feature behaves. Does it cut in and out? Does it give less braking force so that it only generates a certain amount of voltage/current? Someone out there must be using regen braking and a 58.8 or 58.4v battery. What happens when you use the brakes when your battery is still more less fully charged?
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I'll find out myself by the end of the week anyway. I start soldering Monday, building it at work because I have a lot of downtime and the fire risk is less there lol.
I had planned to build a battery over the winter but then decided to just buy one. I'm not rich so after shopping around and googling sellers names ordered one from China on eBay. I'd seen the sellers name on a few forums and mostly good things, no shipping issues at least. You expect to see threads about something failing, people usually only post their bad experiences, but most for this guy were good. Anyway, waited almost 3 months for the battery, seller was in communication the whole time, always had a reason for the delay. Finally I asked eBay to step in and got my money back. Two weeks ago I bought a stack of new laptop batteries at a great price, works out to $1.50 per cell. So here I am well into the cycling season rushing to build a battery. I'm still riding around on my SLAs but they have almost 1000kms on them now and current delivery is lacking to say the least lol, I'm running them in parallel at 24v for the last 100kms or so. For now I'm going to charge 2 halves in parallel on a Hobby King 8s charger but I have a 14s BMS on the way and I'm building my own charger for charging the whole thing at 58.8v. I was going to buy one but I have all the parts already and like I said,I'm not rich lol.
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Hi Alan
To be honest, I never even considered that someone would disconnect the battery from a motor they were using! Open circuit regen voltage could be just about anything.
Hi Dennis,
It doesn't necessarily have to be "someone" disconnecting the battery from a motor they were using, some users occasionally ride their bikes without having a battery attached, or they sometimes have it attached but leave it switched off until assistance is needed, and this caused a lot of problems with the earlier controllers.
With the battery attached and turned on, if you start a trip from the top of a steep hill with a fully charged battery, the regenerative output voltage from the controller during high speed braking could exceed the maximum charging voltage of the battery, and under these circumstances I would expect the battery's BMS to disconnect the charging supply in order to prevent the regenerative braking from overcharging the battery.
However, if a home made battery pack does not have a BMS to protect it from overcharging, the cells could possibly be overcharged, which can be very dangerous with LiPo packs!
I have my MP4 controller maximum voltage set to 59V instead of the default 63V to hopefully protect my 14S lipo pack, but I don't know whether this high voltage cutoff has ever been activated. ::)
My wattmeter does not store the maximum voltage, but I do have a very useful alarm and data logging function on my CellLog 8S battery monitor (http://www.hillrc.com/EnProductShow.asp?ID=96):
(http://www.arhservices.co.uk/GoldenMotor/LiPo/Alarm_zpssdddxdrw.JPG)
I use this to monitor one half of the pack at a time, and I have never had the overvoltage alarm activate on either half. ;)
Here is a graph showing the voltage variation throughout a test ride:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/CellLog%208%20graph_zpshjh9n0rb.JPG)
The high peaks show the regen voltage and the low bits show the voltage sag in the battery when the motor is under maximum load, and the highest cell voltage does not exceed 4.2V (which is the maximum permissible charging voltage for these LiPo cells).
Although I did manage to make the low voltage alarm sound a couple of times while on this ride with an old and weak 8 cell LiPo pack:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/Load%20test_zps7qvbeyfm.JPG)
Some users occasionally ride their bikes without having a battery attached (or they sometimes have it attached, but leave switched off until needed), and this caused a lot of problems with the earlier controllers.
Alan
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Hi Sam.
I want to start out by saying I'm sorry for hurting your feelings. I'm just a bad tempered evil old geezer who clearly hates all form of life, and disagrees with everything said by anyone. So please don't ask to get me kicked off the board. Again.
Whoever explained regen to you had no idea how a generator/battery set works. Find a different source.
Hi Dennis
the explaination comes mainly from my daily work (Automotive) with BLDC (and asynch. eMotors) and the electronic we use there.
What do you think (in particulary) wrong so we could point it out? I build the complete battery electronic (incl. the superCap storage) by myself and it works in the about ten bikes we used 2012 as a ProofOfConcept for the German Train company. It includes an extensive computer system so current/voltage is logged in every current-carrying module (so every (8) LiFePO4 cell is logged, the 12 Supercaps are controlled, the max in + out, GPS position, temperature, ....).
Cheers
Sam
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Hi Alan
To be honest, I never even considered that someone would disconnect the battery from a motor they were using! Open circuit regen voltage could be just about anything.
I agree with your comment about 0.4 VDC battery constuction difference being nothing to worry about. My concern was using 58VDC supply voltage if you know you have caps that are rated at 63VDC . It just isn't a good idea. I believe GM management learned from the "48Volt" MP III disaster, and have uprated the cap rated voltage on current production product.
At any rate, my external controller is still working just fine:)
TTFN,
Dennis
Hi Dennis
I guess Alan means what I (tried to) describe: the BMS have to cut of the external Voltage source just to keep the cells in save range. As most BMS only can dissipate about 100-250mA this situation is easy to reach. We tested such behavior as my first project was to use the MP3 for a Downhill (or better Uphill climber) bike. The GM patched solution to prevent the controller (MP3) to burn itself was to establish a reverse diode on the fuse, but effect of the BMS is the same: it simply cuts of the battery (drain) from the motor (source) to save itself. In all my experience and what I've read the controller (the FET bridges of course) then burn the energy to safe itself (therefor the voltage does not reach infinity which it would do without a powerdrain). I think the GM tech who explained it to me was also named Denis or so. I still have the mails I exchanged in 2012 with GM and could (with lots of effort) look it up.
BUT: the battery voltage drops quite a lot (no matter what Li chemistry is used) in the first few percent of power draining so the situation (Battery dismounts itself as power drain) and the BLDC controller has to burn the energy) is very unlikely else you live on a hill and start your day with freshly loaded cells.
Cheers
Sam
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Hi Dennis,
It doesn't necessarily have to be "someone" disconnecting the battery from a motor they were using, some users occasionally ride their bikes without having a battery attached, or they sometimes have it attached but leave it switched off until assistance is needed, and this caused a lot of problems with the earlier controllers.
With the battery attached and turned on, if you start a trip from the top of a steep hill with a fully charged battery, the regenerative output voltage from the controller during high speed braking could exceed the maximum charging voltage of the battery, and under these circumstances I would expect the battery's BMS to disconnect the charging supply in order to prevent the regenerative braking from overcharging the battery.
However, if a home made battery pack does not have a BMS to protect it from overcharging, the cells could possibly be overcharged, which can be very dangerous with LiPo packs!
Alan
Hi Alan
just seen it that you already answered it. I used a Celllog8S in the first go, and it's the finest log I've seen today: low prices, very accurate, enough storage and a good tool (openSource) to analyze it.
Cheers
Sam
P.S.: did you get confused by my statements at first as well (just as Dennis). Didn't think I stated anything else than you or Dennis himself did.
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That's one half done. Went quicker than I expected, plus no one asked me to do anything today so I mostly just worked on this.
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So you are building a lithium ion powered 4 slice toaster?? ;)
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Lol!
Charging for the first time. Only 2A, my PC PSU at home does 9A at 12v, this one only does 3A. The banana plugs for the charger fit at home too, this breakout board is different apparently. Luckily I had those alligator clips handy. I should probably tape those up lol
Fire extinguisher kept handy. It was between my feet all day soldering yesterday.
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Not surprisingly it couldn't maintain 2A. Kept giving an error after a few minutes. Dialed it back to 1.7A.
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3 Amps @ 12V is only 36W of input power. At 100% efficiency it should only be able to output 1.23A at 29.4V, so 1.7A is very good indeed. ;)
I have recently purchased one of these 12V 30A (360W) LED power supplies as an emergency back-up in case my old power supply dies suddenly:
(http://i.ebayimg.com/images/g/U1gAAOSwpzdWsIDI/s-l1600.jpg) (http://www.ebay.com/itm/351644486265)
At such a low price it seemed to be an obvious choice, and it's a lot lighter (and takes up a lot less room) than the 60Ah car battery I had to use last time. ::)
Alan
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I'm thinking about getting one of those. The PC PSU I have at home is defective. Supposed to put out 12A at 12v. It only does 10.6v and if I charge at any higher than 1A on the charger the voltage drops below 10v on the PSU and the charger shuts down. So it's delivering much less than 1A, I'm too lazy to do the math since it really doesn't matter lol. I can probably get another though, they throw out PCs work all the time.
Here's the battery jammed in its box, perfect fit, you'd think it was made for that. The box is waterproof, I sealed around the power socket and I'm using rubber washers on the bolts that I drove through the bottom to bolt it to the rack.
I've read you shouldn't use those 3 pronged sockets and plugs but that one came off a huge floor model photocopier, it's rated for 15A at 250v, I think it can handle the 18A my motor draws. I used it all last year with my SLAs.
There's a fuse in the empty space below the switches as well as the precharge resistors, the BMS will go in there too once it arrives.
I have another question regarding regen. With my SLAs when braking going down a big hill to work the voltage would go up 5 or 6v. This morning with my lipos the spike was only 1 or 2v. Why? I didn't have a fully charged battery, it was about 54v when I left home, I figured since I don't have my BMS yet I didn't want to risk overcharging when braking. Is it because of the higher capacity, 20Ah vs 10Ah? Is there some property of Lipo that caused it, ie greater internal resistance? Just curious, it doesn't really matter.
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Had a brain fart when I got home, connected the balance leads in parallel before disconnecting the two halves from series. Whoops. Lots of smoke and sparks and burned fingers from tearing the wires apart before it set fire to the tape and plastic and no spare balance leads later leaves me unable to charge my battery until I can get new leads which will take weeks. Ugh. I have some 4 pin connectors, I'm going to try to make 8s out of them.
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Only 1 of the connectors is melted. I just need to pick up some wire and I'm good.
I'll charge one half at a time from now lol. My commute is short enough and my capacity high enough I can do one each day alternating it's just till I get my BMS in the mail anyway.
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Had a brain fart when I got home, connected the balance leads in parallel before disconnecting the two halves from series. Whoops. Lots of smoke and sparks and burned fingers from tearing the wires apart before it set fire to the tape and plastic
Oops. :o
I did a similar thing once when I inadvertently connected two 7S2P packs in series while their balance leads were still plugged into the balance board in parallel. One of the battery connections instantly vapourised as I started to push it in. Fortunately it didn't make a permanent contact or things would have been a lot worse.
I initially thought I had just ruined a battery connector, but I later discovered that it had also damaged several of the tracks on the rear of the balance board:
(http://www.arhservices.co.uk/GoldenMotor/LiPo/BB2.JPG)
(http://www.arhservices.co.uk/GoldenMotor/LiPo/Damagedtracks.JPG)
So I ended up bridging the gaps in the tracks with some unsightly soldering :
(http://www.arhservices.co.uk/GoldenMotor/LiPo/Mendedtracks.JPG)
(It's time I invested in a fine tipped temperature controlled soldering iron for these kind of soldering jobs)
It's surprising how quick and easy it is to produce additional unwanted hassle (and instant excessive heart pumping) with just a split second lapse in concentration.
Fortunately, you were not seriously injured, and no explosions or fires were caused!
Hopefully you have learned a valuable lesson and won't ever do it again.
(http://www.arhservices.co.uk/GoldenMotor/emoticons/fingerscrossed.GIF)
Alan
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No, never again. Charging them one at a time from now on lol. Just in case something else happens though I bought a fire extinguisher yesterday. :)
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Ok, I have failure of my MP3 controller early and I got new (last) version of Magic Pie 3 controller witch I heard that is better from regular when it comes with kit. I notice that this controller has some improvments...First, I notice that regenerative braking works now in 2 modes. When I start to breaking with regenerative from 40km/h, on first contact, regen is start to work normal, then when I slow down to 15km/h, regen is automatic switch somehow to double strongest breaking force. This behavior is not was present on my first regular Magic Pie 3 controller. In a mean time, I was made a battery for my ebike with 58.8V and 50AH (other words...POOOOOOWEEEERRR !!!) and have autonomy more than 500km ;D But, never mind for battery, let's back to case... :)
When the battery was on 58,35V yesterday I was try to make a regenerative breaking with allmost full battery. I made 49km/h max on flat road and press brake. I notice first that mp3 is start to brake on that speed, but after half second, something is release it and stop to brake and after again 100-200ms it start again to brake and after that is just stop and refuse to brake even if I all time hold the brake. So I see in that moment in my analyser that voltage in moment when breaking is stop, the display in this moment show 67,50V ??? I don't get it how, but I notice that this voltage get always in this moments when second time stop to brake...I think that BMS is stopping this and doing this kind of protection to not overcharge a battery with this kind of regenerating. One thing I don't get it...If analyzer show me over 67 or 68V, how I not blow a capacitors in controller ? :) Maybe this is impulse power first...I don't know...It's verry strange, but it's safe because I try this manu times to do this and everthing work like a charm...still :)