Bosch 36V fatpacks opened up

[Russell]

Got curious so just ordered a fatpack for $45 shipped. Sheesh... that's seriously cheap. Going to hammer on it to see what it can do, but can always harvest the 20 VT cells to add to the 40+ raw ones I've already got.

Ya might want to talk to Theyerb about the merits of running an ebike on one Fatpack

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=8767&p=133772#p133679

-R

 

[pwbset]

Ya might want to talk to Theyerb about the merits of running an ebike on one Fatpack

Yeah, had read that. The controller I use is 19v LVC and the shunt is soldered fully so can handle whatever the fatpack wants to give (up to the 60a blow point I would guess.. probably set a 40a limit on the CA just to be safe). I'm really wanting to see what an individual pack can do because I'm looking for about a 4mi "town" range for groceries and what-not and don't want to lug 20lbs+ of konions around with a big batt pack. I'm banking on a single fatpack being able to deliver at least 500w (that's only like 15a under load). At ~80wh per pack I think 4mi isn't too unreasonable to ask.

 

[D-Man]

Anyone know how long the voltage stays above 40 volts for a 8-10 amp load? Or is it always below 40. This would be for like 4-5 packs in parallel.

 

[dnmun]

i think you are safer with a higher initial charge than with a lower final charge potential. lifepo4 is not damaged by brief periods above the 3.7-3.8V sorta where the informal high is thought to be. it can actually be charged higher without damage if for a short time. make sense?
with lipo, you can't overcharge or they cook.

but for reasons i still don't uinderstand. when the battery is forced to deliver power below the 2.1V threshold where the discharge curve drops like a rock, the cell doesn't seem to ever survive. so it would be better to push than ride if you are down below 2.2V on any cell, maybe 2 would be the max, but i consider using them in that regime to be more destructive than charging them to full potential and getting the last 25% of capacity available above (41/12)V.

 

[D-Man]

Oh, I'm talking about discharging them while riding. Example: For me, with sla's I start out under load going down the road 20-21 mph at 43 volts. At the end of my ride I'm at 40 volts under load after 12 miles. I find the range of 39-37 volts too slow. So If I got the bosch packs, I assume it will be too slow or 39.9 volts or less the entire trip. The voltage of the Bosch packs must sag some when you open the throttle. How much?

 

[Russell]

Oh, I'm talking about discharging them while riding. Example: For me, with sla's I start out under load going down the road 20-21 mph at 43 volts. At the end of my ride I'm at 40 volts under load after 12 miles. I find the range of 39-37 volts too slow. So If I got the bosch packs, I assume it will be too slow or 39.9 volts or less the entire trip. The voltage of the Bosch packs must sag some when you open the throttle. How much?

I can't quote exact numbers but when my 3-pack is charged to just over 41.0V it will maintain 39.0V for perhaps 5-6 miles which is better than my original 36V SLA pack and it will continue to feel stronger for at least 10-15 miles out of say 24 miles total. I also ran my ebike with 3-12V and 1-6V SLA and while the 3-Fatpacks I'm using now aren't quite as strong as that they are fairly close (fastest average trip time at 42V = 17.7 mph and w/Fatpacks best = 17.4 mph). They will however spend a good part of their discharge time under 37V just like any 10-cell LiPo or LiMn pack will do if you run them until they are nearly fully drained. Of course there's nothing stopping you from running Fatpacks with a booster and that's exactly what I am considering. My SLA batteries only have 20 cycles on them so I could use one of them with the Bosch pack and start out with about 54V. And when one SLA is used up I'll have two more waiting in line :wink:

-R

 

[Russell]

Rode today and jotted down some data during the ride to get concrete numbers.

Conditions:

Cold, 42F (6C)
Wind ENE @ 12mph (19kmh)
Sunny

All voltages recorded while holding as close as I could to 6.0A (~1C for my 3-pack). Pack charged to 41.47V.

1Ah: 39.0V
2Ah: 38.0V
3Ah: 37.2V
4Ah: 36.1V
4.5Ah: 35.2V
5.0Ah: 34.5V
5.5Ah: 33.6V

At 15.0 miles (24km): 3.2Ah used, avg speed 15.6mph (25kmh)

At 32.2 miles (51.5km): 5.7Ah,212Wh used, avg speed 16.5 mph (26.4kmh), Vmin 31.82V, 34.7V resting after ride.

-R

 

[XRuss]

Good solid info Russell. Thanks for the follow-ups. XRuss

 

[EVTodd]

I'm sitting here trying to solder in some external wires on my Bosch pack (I'm going to parallel 3 together) and I've got myself wondering if I need to keep the circuit board that's inside the pack.

I assume all it does is work as a volt meter for the little led battery indicator and a temperature sensor. It's a pain trying to find a good place to solder the wires in. Am I crazy for thinking about yanking the board off or should I leave it to make sure the cells don't ever overheat?

 

[Russell]

I removed the tops of the packs with the circuit board and tossed them then soldered wires directly to the red and black leads coming from the battery.

-R

 

[EVTodd]

I removed the tops of the packs with the circuit board and tossed them then soldered wires directly to the red and black leads coming from the battery.

-R

I was just reading through your whole post again and saw that. That's what I get for being in a hurry. I'm going to chuck the board too. I think it will be a lot easier that way. Thanks for the quick reply.

 

[John in CR]

Don't chuck the board. You'll need it if you ever use the Bosch charger to charge your pack. It doesn't need to be part of your pack though and taking it off will make your 3pack significantly smaller.

John

 

[Russell]

The LiPo charger I bought from ecitypower on eBay for $24 (delivered from China) arrived last week and here is a picture of it side by side with my SLA charger that I used temporarily;


View attachment Bosch 048.jpg


They not only look the same on the outside they have the same circuit board on the inside. One problem with the LiPo charger was that it came with a 250V Euro style ac plug. The seller sent me several emails asking about how I planned to use the charger and if I had any special connector requirements. I told him to leave the output leads bare, which he did, so I could install Anderson connectors but I never thought to tell him I wanted a 120vac North American style power plug on the thing. Luckily the rating plate states the charger works on 100-240vac, 50-60Hz so I found an old power cable and spliced it in. I then opened the unit and adjusted the output to my preferred setting. I monitored the first couple of charges to make sure it worked properly. The front LED goes from red to green at 41.09V at 0.16A and if I leave it connected for an hour or two it’ll finally settle out at essentially zero current and 41.16V.

-R

 

[TPA]

Can you demo how to change the output settings on the charger?

 

[pwbset]

Doesn't the fatpack circuit board provide LVC cutoff at least? I know they don't balance the cells, but how do their power tools shutoff without killing the packs?? They must have LVC somewhere.

 

[Russell]

Can you demo how to change the output settings on the charger?

Take out 4 screws from the bottom then adjust the red trim pot near the output cable (ccw increases voltage).






-R

 

[Russell]

Doesn't the fatpack circuit board provide LVC cutoff at least? I know they don't balance the cells, but how do their power tools shutoff without killing the packs?? They must have LVC somewhere.

I see of no way that the circuit board can shutdown the pack since the positive and negative leads from the cells are directly soldered to the output connectors. I have never used the packs as intended but they do have a battery charge indicator on the top cover which I imagine you're suppose to look at and charge when it says the pack is low. There is no individual cell monitoring.

My controller has a 31.5V LVC and while the pack generally will kiss that voltage after a 24-32+ mile ride the pack resting voltage is usually in the 33-34V range when I call it quits. Only once have I run the pack completely down to the LVC and held it there but that still works out to a 3.15V/cell average. Unless there is a bad cell that seems like ample headroom to make sure the cells are not over-discharged. I've used my 3-pack for 10 cycles so far and only time will tell whether they hold up.

-R

 

[EVTodd]

Wow, that's interesting. I wonder if I can just adjust my 36 volt sla charger for a lower cutoff. I thought I read somewhere that the "float" stage for lithium batteries was different. I did charge my packs with my sla charger but didn't want to hurt them in the long run.

 

[Russell]

Wow, that's interesting. I wonder if I can just adjust my 36 volt sla charger for a lower cutoff. I thought I read somewhere that the "float" stage for lithium batteries was different. I did charge my packs with my sla charger but didn't want to hurt them in the long run.

SLA and lithium batteries have different charging profiles and while the circuit boards in my two identical looking chargers also look identical there must be a small difference somewhere on the board because they work slightly different.

When I use the 36V SLA charger to charge my 3-12V SLA pack the current starts at max then slowly declines the entire time while the voltage steadily increases. The voltage will continue to increase to 44.0V and when the current falls to 0.40A the charger's LED goes from red to green and the voltage goes to float mode, 41.0V in my case. Leaving the charger on for several hours will result in about 4% more energy being stored in the battery as the current eventually goes to near zero.

When I used the SLA charger to charge up my lithium pack I had to be careful to monitor and stop the charging before it went too high. When charging the lithium pack the current went to max (~2A) then only fell a small amount during the charging process. At 41.9V where I pulled the plug the current was still at 1.5A. As soon as I stopped charging the battery voltage fell a couple of tenths then settled at close to 41.5V in a few hours. This is obviously not a gentle way to charge the pack.

When I used the LiPo charger to charge the lithium pack it also started out at about 2A max and then within a few minutes fell to 1.7A but only dropped slightly from then on. When the battery was about 80% full the current started dropping more quickly as the voltage slowly increased the last half volt or thereabouts toward the setpoint. This is likely the transition between Constant Current and Constant Voltage mode though that's something of a misnomer because if you're observing the current and voltage during charging it's never at a constant current or a constant voltage. That aside the "creeping up" to the desired voltage means getting the last 20% of capacity into the lithium pack takes half again as long as the first 80%. When the current reached 0.16A the LED on the front went from red to green and the pack voltage was 41.09V. Leaving the charger on for a couple more hours will get the very last smidgen of energy into the pack (it really is a tiny amount) and the voltage will rise to as high as it can, 41.15V in this case. There is no BMS on these Fatpacks so there is no point leaving the charger connected any longer than this for balancing.

Now if you want to use an SLA charger for these Fatpacks you can and you can either monitor it closely as I did or set it so it goes no further than 42.0V though keep in mind that at least with my SLA charger adjusting the max voltage lower ALSO lowers the float voltage the same amount. This means that I would have to set the unloaded charger output (float mode) for about 39.0V for a maximum output of around 42.0V during charging. Once it gets to 42.0V and 0.40A (for my charger, your threshold current will differ) it would revert to the downward adjusted float voltage of 39.0V. This should be ok since the charger should have reverse current protection. I have no experience using an SLA charger on a lithium pack which employs a BMS so I can't say if while balancing it would draw enough current to keep the SLA charger from going to float mode or if you'd actually have to tweak the SLA charger way up and let the BMS keep the cells from overcharging while it also balanced the pack. I would not however recommend using an SLA charger on a lithium pack except as a stopgap measure until you buy a lithium charger (or an adjustable power supply) and even then only if you fully understand what you're doing.



-R

 

[EVTodd]

I think I'll just buy the correct charger. Doesn't seem worth messing around with the wrong one.

 

[John in CR]

Doesn't the fatpack circuit board provide LVC cutoff at least? I know they don't balance the cells, but how do their power tools shutoff without killing the packs?? They must have LVC somewhere.

Yes there has to be something to protect the packs from over discharge, but it's not in the form of a cut in the power mains like a BMS does. Instead it has to be something that tells the tool not to work. That turn off signal very likely comes the circuitry on the pack that controls those charge level indicator LEDs. There are 3 slots in the connector, and all 3 require connection for the charger to work, so it makes sense that the 3rd one also provides the signal for the tool to work. I just don't have any of the Bosch tools to find out for certain.

John

 

[Russell]

Yes there has to be something to protect the packs from over discharge, but it's not in the form of a cut in the power mains like a BMS does. Instead it has to be something that tells the tool not to work. That turn off signal very likely comes the circuitry on the pack that controls those charge level indicator LEDs. There are 3 slots in the connector, and all 3 require connection for the charger to work, so it makes sense that the 3rd one also provides the signal for the tool to work. I just don't have any of the Bosch tools to find out for certain.

John

You're right. I hooked up a power supply to one of the circuit boards I removed and found that the power LED's will not light below 24.0V which would then presumably shut down the tool by communicating this through the center connector. As soon as I went a tenth of a volt above that cutoff the green power LEDs lit when the power button was depressed. I guess if I had actually used one of the packs with a tool then I'd have known that


-R

 

[TPA]

isn't that 2.4v/cell?

 

[pwbset]

isn't that 2.4v/cell?

LiMn can handle 2v/cell LVC without effecting cell life too much I bet. The curve is pretty steep at the end so the difference between 2.4v and 2v isn't very practical in terms of usage/distance etc. so might as well set the LVC higher (if you can) to like 27v and call it good for a 10s string. I'm building several konion packs for this summer that will LVC around 2.7v/cell.

I got my fatpack in yesterday. Delivered charged to 35.9v and I took it up to 41v and will start testing it out with an x5 as soon as I finish hard wiring my crazy Steveo Controllerâ„¢ to all my ebike.ca bits. Throttle/halls etc. all have different connectors... what a pain... there is something to be said for standardization of parts. :?

 

[Doctorbass]

isn't that 2.4v/cell?

LiMn can handle 2v/cell LVC without effecting cell life too much I bet. The curve is pretty steep at the end so the difference between 2.4v and 2v isn't very practical in terms of usage/distance etc. so might as well set the LVC higher (if you can) to like 27v and call it good for a 10s string. I'm building several konion packs for this summer that will LVC around 2.7v/cell.

I got my fatpack in yesterday. Delivered charged to 35.9v and I took it up to 41v and will start testing it out with an x5 as soon as I finish hard wiring my crazy Steveo Controllerâ„¢ to all my ebike.ca bits. Throttle/halls etc. all have different connectors... what a pain... there is something to be said for standardization of parts. :?

All data right here except the 2.0V lvc !.. I personally think the cell would dammadge if cutted as low as under 2.7V.

Mant manufacture recommand 3.0V and also to use around 80% max of the capacity of teh cell so the voltage LVC recommanded goes to around 3.3 to 3.4V for keeping at the 500 cycles at 1C discharge.

LiMn are like li-co and liPo about the LVC.

Doc