see amazing story here;
http://toolmonger.com/2006/04/11/monster-garage-builds-milwaukee-v28-li-ion-powered-dragster/
http://toolmonger.com/2006/04/11/monster-garage-builds-milwaukee-v28-li-ion-powered-dragster/
Monster Garage Builds Milwaukee V28 Li-Ion Powered Dragster
- Thread starter How2
- Start date
vanilla ice
1 MW
Nice rack..
http://blogs.toolbarn.com/brianm/uploaded_images/DSCN0165-719399.JPG
http://blogs.toolbarn.com/brianm/uploaded_images/DSCN0165-719399.JPG
vanilla ice said:
Wait a minute. WTF? We can't seem to wire more than 2 in series without blowing the BMS and you're telling me they did 384? No way. Special packs or special wiring or something. Look at all those beautiful connector blocks. *drool*
Jay64
100 kW
Fechter was mentioning something about this in the EV basics section. He mentioned using diodes to protect the BMS, I don't know if that would fix your specific problem, but something to at least look into.
http://endless-sphere.com/forums/viewtopic.php?f=16&t=1312
http://endless-sphere.com/forums/viewtopic.php?f=16&t=1312
rkosiorek
100 kW
pwbset said:
i don't know but i suspect that having Builders including Milwaukee’s resident battery expert Jon Zick, might have had something to do with that. too bad they don't have any details.
rick
Jay64 said:
This setup should work for the V28 batteries too. You can stack as many as you want in series.
fechter said:
Hmm. Interesting. Thanks for sharing! I wish I knew more about this stuff. Guess it's time to learn. Would still void the warranty, but at least I wouldn't have to have a bunch of wiring sticking out of the packs everywhere... could still use the same connector block assemblies, stock chargers etc. etc. That would rock.
Can you explain to me how this would *prevent* the BMS' from blowing in the first place? I mean since we already know that 3 in series fries it how does a diode prevent that. I can understand how it protects it, but not how it prevents the symptom in the first place.
Also, could you recommend a diode sized specifically for the v28 packs? And where to buy some? I think I might want to try this to get 84v 3s, but I'm pretty noob. A laymen's how-to would be great...
You could put the diodes on the connector blocks instead of ripping open the packs. 
I don't know which wire is which in that BMS.
A 50v, 50 amp diode would be good. A lower amp rating might be OK, I don't know what the maximum current for a V28 battery is. The diode only has to take the voltage of a single pack no matter how many you put in series.
When you put multiple packs in series and one pack decides the current is too high and switches off, the combined voltage of the whole string will be across that switch, exceeding it's voltage rating and causing smoke.
By placing a diode across each pack, if the switch opens, the diode will conduct, limiting the voltage across the switch to one pack voltage plus the drop in the diode (~1v), keeping the BMS happy.
Without the diodes, the voltage to the controller will drop to near zero if any pack trips. With diodes, the voltage to the controller will drop by one pack voltage if one trips.
I hope this makes sense.
I don't know which wire is which in that BMS.
A 50v, 50 amp diode would be good. A lower amp rating might be OK, I don't know what the maximum current for a V28 battery is. The diode only has to take the voltage of a single pack no matter how many you put in series.
When you put multiple packs in series and one pack decides the current is too high and switches off, the combined voltage of the whole string will be across that switch, exceeding it's voltage rating and causing smoke.
By placing a diode across each pack, if the switch opens, the diode will conduct, limiting the voltage across the switch to one pack voltage plus the drop in the diode (~1v), keeping the BMS happy.
Without the diodes, the voltage to the controller will drop to near zero if any pack trips. With diodes, the voltage to the controller will drop by one pack voltage if one trips.
I hope this makes sense.
Jay64
100 kW
Fechter, thanks for explaining that in more detail. I have milwaukee packs and dewalt packs and not having to take them apart would be great for me. I still use the milwaukee packs with my set of cordless power tools.
fechter said:You could put the diodes on the connector blocks instead of ripping open the packs.
Oooooh! Now that sounds fechtacular there! I still don't really understand where to put the diode on the connector block assembly, but there are only three terminals and I think I know + and - now and I think I get the general concept and am going to try it out next week. If I can find some diodes at a local electronic store I'll post a new thread with my attempt. I may ask for help here and there.
Sounds pretty simple in theory though. Thanks a million for sharing! This would open the doors for all kinds of configurations and still maintain the warranty!I assume that if... or more when... a BMS trips the diode would take over until the BMS "rebooted" and put the pack back in series? If this happens a ton would it even be worth doing this mod? I gotta assume it wouldn't happen that often if those guys could do 384 in series and maybe jondoh/maytag just surged there's really badly or something? Has anyone else blown Milwaukee BMS?
If you try to draw more current than the BMS allows, it will trip.
If you have the current limit on your controller set slightly below this level, the BMS should never trip until you hit the low voltage cutout. If one trips on high current, the amp draw should immediately drop and it should reset. You might have to back off the throttle to reset it.
The dragster guys must have the BMS bypassed.
I'm not sure what the 3rd wire does, but the diode goes across the main + and - wires on the block.
If you have the current limit on your controller set slightly below this level, the BMS should never trip until you hit the low voltage cutout. If one trips on high current, the amp draw should immediately drop and it should reset. You might have to back off the throttle to reset it.
The dragster guys must have the BMS bypassed.
I'm not sure what the 3rd wire does, but the diode goes across the main + and - wires on the block.
fechter said:
OKay... just so I'm crystal clear here. Current = amps. People have been saying that each v28 BMS is rated to 15A... I think?? 2 in series works... 30A, but 3s @ 45A max pops it??? So... if my Crystalyte 72v20A controllers maxes out at 20A (30ish peak burst) it should be fine in 3s by default right? Dare I try it?
Jay64
100 kW
pwbset said:If I can find some diodes at a local electronic store I'll post a new thread with my attempt. I may ask for help here and there.fechter said:You could put the diodes on the connector blocks instead of ripping open the packs.
A lot of EV shops, like http://www.thunderstruck-ev.com/ sell the diodes.
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