DIY Battery Packs (Yard Works)

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Looks like it's time to replace my battery pack (48v), and was wondering what those DIY'er's are building packs from?  Yard Works packs from Canadian Tire seem to have gotten some good review's.   Some good thing's were posted here... http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=4908&start=0&st=0&sk=t&sd=a  These pack's are 20v / 6AH Lithium Ion. I would like to run 3 of these batteries in series, but I'm thinking the Magic controller is NOT going to like that (60v).  My other option would be to run 2 (40v), but I think that would trip the LVC and render it useless?  Anybody have any experience with these or other packs (Dewalt / Makita / Yardwork's, etc)??  I would like to stay away from "prebuilt" unit's, and try to save some $$$ building my own. 

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For anybody interested in the result... just got back from Canadian tire, charged up the batteries and held my breath as I connected.... and she came to life.  It's raining too hard out to really give them a go but I did put the front tire up against the wall and do a burn out to make sure everything was operating fine   Now the only question is how long the controller will last with the extra volt's running through it.  Anybody interested in trying this, the total cost for the 3 batteries was $413.97 (after taxes) plus chargers (39.99 each).  I will update later when it dries up some....

[MonkeyMagic]

Hmm I'm scratching my head wondering why didn't you get a GM 48v 12Ah from goldenmotor.ca instead? 
So much less hassle and cumbersome. I guess each to their own tho..

Also with 30A max discharge you should limit your controller to <30A Max as I assume it's set at the default ~45-50 Max.

The MP Controller is good for 63V. But then 60V @ 6Ah battery I'd be suprised how much range you would get past 20km's [12mile]

Let us know some stats!

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Well, I wasn't going to get into the reason I didn't buy the GM battery, BUT.... the first battery I had was that exact one, and to be honest it was not very good (and I'm being kind) but that's another story.  I'm not too worried about range, the most I really need to travel is 15km... and I think this battery suit's my need's.  Anyway's, just took the bike out for a rip.  I can say that the biggest surprise was the increase in torque.  Bike pulled alot harder starting off/midrange.  Top end felt about the same, maybe a touch faster (I'll GPS to find the exact top speed later).  Controller was warm to the touch after going WOT on and off for about 5 minutes.  I will definitely need to keep an eye on that, probably get a temp gauge mounted on my handlebar's.  At this point it's really too early to say anything about range, durability, etc.  After a week or so I will give a more in depth review of the batteries.  I use my bike everyday so I should have a fairly good idea at that point.  Good idea about limiting controller... thanks!

[Leslie]

Well, I wasn't going to get into the reason I didn't buy the GM battery, BUT.... the first battery I had was that exact one, and to be honest it was not very good (and I'm being kind) but that's another story.  I'm not too worried about range, the most I really need to travel is 15km... and I think this battery suit's my need's.  Anyway's, just took the bike out for a rip.  I can say that the biggest surprise was the increase in torque.  Bike pulled alot harder starting off/midrange.  Top end felt about the same, maybe a touch faster (I'll GPS to find the exact top speed later).  Controller was warm to the touch after going WOT on and off for about 5 minutes.  I will definitely need to keep an eye on that, probably get a temp gauge mounted on my handlebar's.  At this point it's really too early to say anything about range, durability, etc.  After a week or so I will give a more in depth review of the batteries.  I use my bike everyday so I should have a fairly good idea at that point.  Good idea about limiting controller... thanks!

Limit your controller amps = limit your duty cycle = limit your throttle.

The way I do this to a massive overvolted hub is to ride up my steepest hill and l adjust the trottle so I can feel the smallest loss of power when I edge off the twist throttle headibng up hills.

Try cooling it.

Just need a some good air circulation.  Or I thought of turning massive regen into cold by peltiers but this is in another universe ATM.

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I made an enclosure for my controller out of fiberglass with a very large opening in the front that faces forward to help keep it cool.  When I first got the kit I had everything in panier's and it just got too hot.  This seems to keep the controller much cooler.  Haven't had any issue's since.  I've seen some guy's drilling holes in the side of the motor cover to get better ventilation, but I think that's alittle extreme especially since I occassionaly get caught in rain.  I briefly thought of water cooling the controller with a CPU block, but again this would probably be overkill (and a huge PITA).  I really don't expect to spend much time WOT...  mostly I'm just commuting to work on public road's so I'm trying to not attrack alot of attention as it is. 

[MonkeyMagic]

Hmm wouldn't be worrying too much about cooling the controller... You can cool it all you want but the 'Yardworks' battery internal BMS is rated@ 30A Max discharge according to the info link posted.

Maybe hook up a temp gauge to the battery instead

[Leslie]

Just as a point,

An LM338 can do 3 amps no heat sink and with a large heatsink it can do 5 amps, with some active cooling it can do 8+ amps.

That cooling certainly doubled it ability to carry current, the same applies to most silicon components.  Its the volts that breaks down the component barriers, and the heavy load and current draw that heats and burns them up.

Cooling will take the heat away that causes resistance that creates more heat.

Too much heat makes too much resistance and too much resistance over a small area with a high load and current draw equates to a larger voltage drop over the source and drain, and that equates to more watts wasted around the gate and that creates heat more, slows down switching and just makes life really hard.. Thermal runaway occurs just like this.



If the controller is getting too hot cool it or take away all that jump out of the box power away youre enjoying now..

[Leslie]

Hmm wouldn't be worrying too much about cooling the controller... You can cool it all you want but the 'Yardworks' battery internal BMS is rated@ 30A Max discharge according to the info link posted.

Maybe hook up a temp gauge to the battery instead

Does his motor draw more than 30 amps?  If so, cool the BMS too.   

Edit:

You are correct for posting this fact too.

[Leslie]

Ok I finally googled something.  LOL.  Glad I did though.


http://en.wikipedia.org/wiki/Thermal_runaway

Semiconductors

Silicon shows a peculiar instability. Its electrical resistance increases with temperature up to about 160 °C, then starts decreasing, and drops further when the melting point is reached. This leads to thermal runaway phenomena within the semiconductor junction areas; the resistance of the area which becomes hot above this threshold decreases, more of current flows through it causing yet more heating in comparison with the surrounding areas, which leads to further temperature increase and resistance decrease. This leads to the phenomenon of current crowding and formation of current filaments, and is one of the underlying principles beyond many semiconductor junction failure mechanisms.

Wow the resistance decreases the further you go into runaway.  I knew about the initial increase.  

Like a resistor I thought the more heat increased the resistnace to the current flow but the current draw over rides this and creates a larger voltage drop at the same current draw meaning more watts being used over the resistor.  As long as the full circuit resistance does not equate to impede the current pathway you will get a a larger voltage drop over a resistor with no loss of current supplied to the said device.

I think part of my theory is correct.

The battery, BMS fets and controller fets will never restrict ample current to a motor to protect themselves by heating up, They will die trying to supply the current required by the device, so the thermal runaway is quite possible.

This all rather interesting.  Why does the resistance get lower in the end process of thermal runaway, how can something that be so full of energy its melting desire to concuct more?  

Is this where combustion begins to take an electrical effect over the material?

[Leslie]

http://en.wikipedia.org/wiki/Thermal_runaway

Power MOSFETs

Power MOSFETs display increase of the on-resistance with temperature. Power dissipated in this resistance causes more heating of the junction, which further increases the junction temperature, in a positive feedback loop. (However, the increase of on-resistance with temperature helps balance current across multiple MOSFETs connected in parallel and current hogging does not occur). If the transistor produces more heat than the heatsink can dissipate, the thermal runaway happens and destroys the transistor. This problem can be alleviated to a degree by lowering the thermal resistance between the transistor die and the heatsink. See also Thermal Design Power.

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I posted about cooling the controller because I've had issue's in the past with keeping it cool.  I quickly learned that you can't keep the controller in a panier bag in the summer month's as it just get's way too hot (I'm sure some people do with no problem's...)   The Yardwork's batteries (the casing anyways's as I've left them intact) barely even get warm.  So I'm not really concerned about them.   Appreciate the tip's though!!

[Leslie]

I posted about cooling the controller because I've had issue's in the past with keeping it cool.  I quickly learned that you can't keep the controller in a panier bag in the summer month's as it just get's way too hot (I'm sure some people do with no problem's...)   The Yardwork's batteries (the casing anyways's as I've left them intact) barely even get warm.  So I'm not really concerned about them.   Appreciate the tip's though!!

Monkey Magic was not concerned about your lipos getting hot as the resistance is meager in that sort of get up, he was concerned about your BMS output switches.

The lipos are a lose cannon in the face of a good load through the BMS.  If your controller is getting warm he asumes your BMS is too.  He is correct and it maybe worth watching the temp on the BMS output solid state circuits.

Just to be sure thats all.  Dnmun at ES will yell all blue about adequate ventilation when concerning Ping batt BMS.  But thats a Ping BMS.
You need to make sure the motor does not exceed the BMS rating becuase the cells will.

All that depends on the BMS and whether or not its shunted to protect the output.  No harm in checking.