Over voltage and regenerative braking

[Thuktun]

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.

[Thuktun]

Not surprisingly it couldn't maintain 2A. Kept giving an error after a few minutes. Dialed it back to 1.7A.

[Bikemad]

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:



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
 

[Thuktun]

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.

[Thuktun]

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.

[Thuktun]

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.

[Bikemad]

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. 

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:





So I ended up bridging the gaps in the tracks with some unsightly soldering :


(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.



Alan
 

[Thuktun]

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.

[Dachawave]

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 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