Bosch 36V fatpacks opened up

[icecube57]

Look imma tell you my personal experience.... Ive drug a bosch pack down to 0v for more than an hour. I forgot about it and it was on a dummy load to test capacity. I took it off the load. The voltage slowly popped back up to 18-19v. I put it on a 36v LION charger. It didnt seem to care that the voltage was low and it charged back up normally. Discharged it again and it gave me the normal capacity with no ill effects. The pack actually seem to perform better. It held its voltage alot better especially near the "knee" of the discharge.

 

[The Stig]

I'm leaning towards making a Bosch Fatpack battery. I'm thinking of making a 15S4P battery from 3 fatpacks. So 55.5V 4AH.
Gonna be charging them with a Ping 60.5V 5A charger... which means a 1.25C. Is that charge rate slightly too high for these cells? I know the Bosch charger charges in 1 hour which I believe to be 1C.

Unless there is a better source for cells with this type chemistry, LiMn...
Does anyone know about the best place to buy Fatpacks these days?
I found this on ebay and might go for it if thats a good deal: http://cgi.ebay.com/Bosch-BAT836-36...emQQptZLH_DefaultDomain_0?hash=item518e9f56ec

 

[John in CR]

Ice,
Interesting, but I'm still not going to run my 10 fatpack pack down to zero. I have brought some Konion cells back from the dead.

Stig,
PM Doc Bass and see if he has any Makita packs. They're the V cells, not VT, so a little lower power but 20% more capacity. I just paid $336 including shipping for what will turn out to be about 200 good cells to make a 1.1kwh pack that I have to assemble.

Also, you really don't want to cannibalize Bosch pack like you're talking. The cells in the packs are staggered not touching each other to allow air flow. As a result they require that unique support structure, so if you start hacking on the cell arrangement, you will have to cut every tab, and multiplied your work 10X and risk to the cells 50X. If they aren't kept stacked the same with the same odd support structure, you will put stress on the tab welds and you are begging for trouble. You may be able to get away with cut it in half lengthwise, but I've never tried it.

The used Makita packs, on the other hand, are a piece of cake to get what you want, and the cells are arranged in a nice straight line, so they are easy to support, and some of the tool packs come with useful rubber to use for support. You'll need the right size torx security wrench (kind like an allen wrench, but a star shape with a hole in the end of the wrench). You'll also want a pair of tin snips for cutting the dead cells off and retaining as much tabbing as possible without stressing the welds of the good cells.

Once you weed out the bad cells, creating a 2p15s string would require just 3 new solder joints, and it's overlapping tab on tab, so even a caveman solder guy like me can do it without heating up cells. I should do a thread with pics this go round, because I've whittled this recycling process down to what I believe is its simplest form.

Regarding the charging, I wouldn't go that fast in the interest of longer cycle life, but the Bosch chargers put out 3.5 amps for 2p packs, so your number is possible. The Bosch charger includes active ventilation of the pack while charging and thermal monitoring. Without both, anything faster than a 2 hour charge may be a bad idea. My smallest Konion pack is 6p, and it gets slightly warm during use and maintains that warmth if I charge immediately after use with the Bosch charger connected to the sealed DIY pack.

John

 

[pwbset]

Also, you really don't want to cannibalize Bosch pack like you're talking

x2 The tab welds in the Fatpacks are some of the burliest I've ever seen... not at all easy to harvest individual cells from. Makitas are MUCH easier to harvest the cells from 'cause the welds are so much smaller (and probably part of why so many of those fail heh, heh).

 

[John in CR]

Also, you really don't want to cannibalize Bosch pack like you're talking

x2 The tab welds in the Fatpacks are some of the burliest I've ever seen... not at all easy to harvest individual cells from. Makitas are MUCH easier to harvest the cells from 'cause the welds are so much smaller (and probably part of why so many of those fail heh, heh).

pwbset,

You couldn't pay me to remove tabs from toolpack cells. Keep as much of the tab in place as possible, and take advantage of the work already done for you. With the typical Makita packs I've worked, I have 8 good cells 2p4s with a nice piece of tab at each end. I join 5 of these together in series with just 4 solder joints that join tab on tab. It just doesn't get easier than that for a 40 cell string of 2p20s.

 

[The Stig]

Guys thanks for the responses. I want to avoid individual cell harvesting if I can! In this post Icyclist describes how to make a 15s pack by cutting one of the fat packs in half http://endless-sphere.com/forums/viewtopic.php?f=14&t=7569&p=190332&hilit=15s#p190332. I would like to assemble a pack in the simplest way possible without too much soldering and if I go with fatpacks I'd like to keep the cells in the plastic support structure as much as possible.
I would like to fit the pack in a box that is about 160 x 130 x 65mm.
The V cells sound good but I'm not so sure about how to find bad cells and how well the pack will stay balanced if I use it down to an LVC of 3V(?) per cell and charge it at 0.8C(5A) up to 4.05V with my LiFePO4 charger. Are there some good posts on how to do what i need to do? I hope its not necessary but Doc boasts matching cells very closely when he built his pack. that sounds like something I can't really do.

Once you weed out the bad cells, creating a 2p15s string would require just 3 new solder joints, and it's overlapping tab on tab, so even a caveman solder guy like me can do it without heating up cells. I should do a thread with pics this go round, because I've whittled this recycling process down to what I believe is its simplest form.

That would be great if you could do that thread. I'm also pretty much caveman-level when it comes to soldering.

 

[docnjoj]

Here is one of the 2 setups I did to get 18 volts at 8 ah. I had to cut the 1 strip between the 2 packs in each Fatpack and solder leads on. The silver thing is a buss (terminal strip) also soldered and screwed) This system allows 16 AH to go with my 20 ah ping in series and can get charged through Y connectors also in series on the original Bosch charger.
otherDoc
View attachment 100_4236.JPG

 

[John in CR]

Nice one Doc keeping the pack string intact and connecting in the center. Did you cut the red part open, or manage to slide the cell array out to do your work?

 

[docnjoj]

Hey John. I had to slit the pack and at first used my ceramic knife but that took too long so I ended up cutting the plastic with a Dremel (carefully). It looks like it should work but we are having SNOW so I won't be going out to test today or tomorrow.
otherDoc

 

[John in CR]

Snow, hehehe I have only fond memories, primarily skiing and snowmobiling...Never really had to shovel or commute in the stuff.

 

[docnjoj]

Please see my post here for a success report on the combine Ping Fatpack marriage.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=16083#p238268

otherDoc

 

[PeteCress]

The Fatpacks are rated at 2.2Ah each which means the cells are 1.1Ah since they use 20 of them in each pack.

There's some kind of convention implicit in the above, right?

Taken literally, it doesn't compute: 20 cells @1.1Ah each == > 22Ah, not 2.2 Ah.

But I've too many similar statements for it to be anything except misunderstanding by Yours Truly.

It's as if 1.1Ah at the "cell" level is different from 1.1Ah at the "battery" level? As in 1.1 Ah(cell) = .011 Ah actual?

 

[pwbset]

Taken literally, it doesn't compute: 20 cells @1.1Ah each == > 22Ah, not 2.2 Ah.

Don't multiply by 20.. multiply by 2 because they are 10 in series and only 2 in parallel. 2 x 1.1ah = 2.2ah. 10 x 4.1v = 41v.

You would be correct if the pack was only 1 4.1v cell x 20 in parallel = 22ah. Make sense?

 

[PeteCress]

Taken literally, it doesn't compute: 20 cells @1.1Ah each == > 22Ah, not 2.2 Ah.

Don't multiply by 20.. multiply by 2 because they are 10 in series and only 2 in parallel. 2 x 1.1ah = 2.2ah. 10 x 4.1v = 41v.

You would be correct if the pack was only 1 4.1v cell x 20 in parallel = 22ah. Make sense?

No - but if I think about it awhile it might upgrade my understanding of amp hours.

Right now, I'm thinking of amp-hours as "How much gas is in the tank" or "How much gas have I used? - which, I suspect, is what watt-hours really is.

 

[Russell]

Amp-hours is one measure of the capacity of a battery and it's fine if everyone is running the same voltage however it leaves out an essential element of the capacity equation. When Ah is multiplied by the Voltage you get Watt-hours which you can then compare to other batteries regardless of their voltage. For example you can have a 36V/10Ah battery and a 48V/10Ah battery but the 48V battery will have 33% more capacity at 480 Wh compared to 360Wh for the 36V pack. Therefore if you maintain the same speed with either pack the 48V battery can deliver 33% greater range.

Getting back to the Fatpack construction they have 20 cells each and each cell is 1.1Ah/3.7V (nominal). The cells are first paired up in parallel to make 10 groups of 2 cells which have 2.2Ah at 3.7V then those 10 groups are wired in series to make a 2.2Ah/37V battery (though it's called 36V).

-R

 

[PeteCress]

Amp-hours is one measure of the capacity of a battery and it's fine if everyone is running the same voltage however it leaves out an essential element of the capacity equation. When Ah is multiplied by the Voltage you get Watt-hours which you can then compare to other batteries regardless of their voltage. For example you can have a 36V/10Ah battery and a 48V/10Ah battery but the 48V battery will have 33% more capacity at 480 Wh compared to 360Wh for the 36V pack. Therefore if you maintain the same speed with either pack the 48V battery can deliver 33% greater range.

Now it makes sense...I think...

Final test: If rider A's CA says they've used 8AH out of their 36v pack and rider B's CA says they've used 8AH out of their 48v pack, rider B used more "gas", right?

And if that's true, then the FatBacks at 37v pick up a few additional points over the DeWalts at 33v bc, although they both claim 2.2 or 2.3 AH the FatBack is going to deliver marginally more watt hours.

Sounds to me like I should have gone the FatPack route instead of buying the two DeWalts I have. Sure, the DeWalts are going to have two or three... or even four times the cycles in them... but with my use, the calendar time to toast the FatPacks would be such that technological advances would probably make them obsolete long before they degraded...

 

[Russell]

Final test: If rider A's CA says they've used 8AH out of their 36v pack and rider B's CA says they've used 8AH out of their 48v pack, rider B used more "gas", right?

Yes...and that's the rub when you switch to a higher voltage you end up going faster (most folks will anyway) and using more Wh/mile so you don't go any further even though you have more capacity.

And if that's true, then the FatBacks at 37v pick up a few additional points over the DeWalts at 33v bc, although they both claim 2.2 or 2.3 AH the FatBack is going to deliver marginally more watt hours.

Probably since 37V x 2.2Ah = 81.4Wh for the Fatpacks and 33V x 2.3Ah = 75.9Wh for the DeWalts but the difference isn't that great. The higher initial voltage of the Fatpacks would of course provide faster speeds but due to their LiMn chemistry the voltage contiunually declines at a steady rate while the voltage of the DeWalts starts out lower but only declines a small amount as they are discharged until close to the end when the voltage plummets. For ebike use it would be nicer if the DeWalts had 12 cells like we're accustomed to for LiFePO4 batteries but then they weren't intended for us. Many folks harvest the cells from the DeWalts to construct a custom pack instead of using them as is.

Sounds to me like I should have gone the FatPack route instead of buying the two DeWalts I have. Sure, the DeWalts are going to have two or three... or even four times the cycles in them... but with my use, the calendar time to toast the FatPacks would be such that technological advances would probably make them obsolete long before they degraded...

If you just wanted a "limp-home" pack when you bought the two DeWalts then I'm sure they will work fine for that. They would also be good when used as is with a faster wound motor like a 9C 2806 or a "24V" or "20 inch" version of a manufacturer's motor. They should even run your 9x7 9C motor faster than the 26"/700C eZee so you might want to try them on that motor.

-R

 

[docnjoj]

So after about a week of riding with the combination rebuilt Ping 36 v 20 ah and 18 v 16 Ah fatpacks it has become routine. Whrs total are less than the Ping only or the Fatpacks only for the same distance but peak watts is down from 38 to about 26. John was right again as I now only use part throttle except on rare occasions. The Ping is mounted low in its new Lexan rack and the Fatpacks are in the panniers. I'm gunna paint the Lexan the same color as the new mirror mast (plastic pipe) and wrap the batteries in orange duck tape so it all matches. It needs a bit more work but it works.
otherDoc
View attachment 100_4239.JPG
otherDoc

 

[TPA]

I fear for your lexan box. My experience is that lexan does not like fatigue. You may or may not experience cracks over time.

Looks fabulous though.

 

[docnjoj]

Thanks TPA. I was wondering about the fatigue factor but it is 1/4 lhick and has hinges with screws and is bolted to the frame. We will see in time.
otherDoc

 

[Loofa]

Not much information on here about the Slimpack BAT818 (1.3AH each) - I can buy 4 slims cheaper than I can buy two fatpacks so I was figuring i'd just wire up 4 slim ones for a total of 5AH vs the 2 fatpacks at 4AH. Makes more sense right?

 

[docnjoj]

Interestingly the 18v 16ah revised Fatpacks are being used at about 1/2 the Whrs of the 36 volt 20ah (nominal) Ping. I did a quick 5 mile run and got about 18 whs for the fatpacks and almost 72 Wh hrs for the Ping. Still not much drawdown but it seems like the BMS of the Ping will shut down way before the Fatpacks run out. I wonder why? Remember these are in series for nominal 54 volts.
otherDoc

 

[PeteCress]

...but I live in a bike theft capital of the world...

NYC?

 

[icecube57]

Interestingly the 18v 16ah revised Fatpacks are being used at about 1/2 the Whrs of the 36 volt 20ah (nominal) Ping. I did a quick 5 mile run and got about 18 whs for the fatpacks and almost 72 Wh hrs for the Ping. Still not much drawdown but it seems like the BMS of the Ping will shut down way before the Fatpacks run out. I wonder why? Remember these are in series for nominal 54 volts.
otherDoc

The voltage is lower on the fat packs. The fat packs make up 33% of your pack voltage therefore they are going to contribute about 33% of your wh consumption. So if you discharged 90wh total the bosch packs contributed only 20%?!?!? Either you gave approximate values or there is funny math going on.

 

[PeteCress]

I like pedal first 'cause then I don't have to worry about hall sensors, which blow, and I also consider it a safety feature when friends (and kids!) check out the bike and twist the throttle saying, "what does this do?" :lol: No need to worry about kill-switches or anything like that. Nice and simple. It activates around 5mph, which, unless you have physical issues, is so easy to get to even on steep slopes. Stand on a pedal half a revolution and vroom off you go.

Does it work the other way?

e.g. You're moving up a hill at 6mph, speed drops to 4mph... does it cut out?