Milwaukee battery rack

[lookingelectric]

I'm considering buying Milwaukee 28V batteries for my upcoming ebike, and thinking about how best to go about connecting the batteries together.

A pile of aligator clips would work, but would be ugly and might be unreliable.

I'm considering the following:

A plastic rack with interfaces that mimic the underside of a Mikwaukee powertool and allow the battery to snap in as if it were going on a tool. The rack would be two-sided with slots for 4 batteries on each side. All batteries would be connected in parallel. +/- copper leads would come out of the end and users would charge the batteries on the ordinary Milwaukee chargers.

The big question: Tooling costs are such that I can't get just one. If I were to have a few made, how many people here would but at about $40 each?

 

[Swordman]

Have a look at this thread:

http://endless-sphere.com/forums/viewtopic.php?t=233&start=0

 

[Beagle123]

Hi looking electric:

I'm considering the same thing right now. I beleive that jondoah unplugs each of his batteries and puts them in the chargers. I think he has 4 chargers. I'm not sure, I've been trying to ask him.


xter gave me some good advise on page 5 of my thread:

http://endless-sphere.com/forums/viewtopic.php?t=1833&postdays=0&postorder=asc&start=60

This was particularly interesting:
http://www.rcgroups.com/forums/showthread.php?t=508443

But once dimantled, how do you charge them? Why not keep them with that nice, handy little BMS?

You might want to get one of these plastic welders to build your battery rack:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41592

I've been interested in these myself. I noticed that my vinyl windows are welded togher. I think you could make some cool stuff.

Please let me know how you create your battery pack.

 

[xyster]

But once dimantled, how do you charge them?

There's two good options for charging if the BMS has been disconnected.

1) Multiple single-cell li-ion/lipo chargers, one per each parallel subpack (e.g. 10 for a 37 volt pack):
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1231
The charger leads can be terminated with Anderson connectors arrayed into a neat block so that the chargers can be plugged and unplugged all at once.
Using this technique, as I do on my li-ion pack, the emoli pack is fully balanced with every charge, and more importantly the risk of overcharge is exceeding minimal because each charger generates 4.20 volts -- the max cell voltage. The chargers are incapable of overcharging cells.
Since the chargers do not have a ground prong or metal casing, they are electrically isolated from each other and so charging simultaneously poses no short-circuit risk.

2) Any good RC li-ion/lipo charger with balancer. This is Patrick Mahoney's technique. See his li-ion pack build thread for more info.

Why not keep them with that nice, handy little BMS?

The milwaukee BMS works fine with any number of parallel'd 7-cell packs, and up to 2 7-cell packs in series (for a 56 volt pack). It is unknown if the BMS's are OK with packs of higher voltage employing more than 2 BMS's in series. One Milwaukee charger can be used per 7-cell, 28 volt group.
This is Maytag's charging technique. See his emoli pack build thread for more info. Keeping the BMS intact with disassembled packs is more of a PITA to wire, and IMHO, provides little safety benefit with these safer lithium manganese cells so long as the pack voltage is monitored with some sort of on-board voltmeter or the CycleAnalyst.
These cells, like other lithiums, tend to stay in balance during discharge, so any discharge balancing the BMS provides is unnecessary, so long as the pack is balanced on every charge, which is probably how the BMS works anyway.

 

[xyster]

Sorry for the multiple postings, I received the attached error message after I posted which seemed to indicate my reply was not getting through. So I tried a few times, resulting in multiple submissions that all appeared to be blocked when they were not. I emailed knightmb about this problem.

 

[xyster]

...

 

[xyster]

...

 

[Jozzer]

Some people will do anything to get their post count up to 3000 :lol:


Edited to add.....I got the same message when posting this, thought the post was made nonetheless..

 

[lookingelectric]

But once dimantled, how do you charge them? Why not keep them with that nice, handy little BMS?

Hi, Beaglet.

The idea is not to dismantle them. The battery packs would plug into the rack as if they were going onto a power tool. Thus, they would stay intact.

 

[Beagle123]

Hi looking:

I'm haven't decided how I'm going to set-up my batteries yet. However, xter has given some great advise. I think we should consider xters point. One advantage to dismantling the battery packs is to save lots of valuable space, and I think his charging method may even be superior to using the stock BMS.

If you look at my situation, I have a huge battery box by ebike standards (11 in X 5.75 in X 7.75in) I figure that I can MAYBE get 8 Milwaukee packs into the space if they fit sideways. If not I can fit only 6. That's 42-56 cells. If I dismantle them, xter and I figure we can use 110 cells.

Obviously keeping the nice neat cases (under warranty) with built in BMS is appealing too.

However, the charging set-up xter describes is really good. It should be very safe, and it will automatically balance the pack. It would have a convenient plug. But also, what alternatives do we have? Unplug each pack and plug it into the charger? I'm planning on 12-16 packs. 12-16 chargers? I could use 8 chargers, and charge half of the packs at a time (not!). As xter said, its unknown if you can wire one charger to two packs and have it work, so you'd then have to take apart each charger and put a plug on it, and plug in all the plugs.

In my situation, my batteries are going to be sealed in a battery box. My only option is to have a plug-in charger. However, jondoah has a nice little bike with 6 batteries that he takes out and plugs into the charger.

Hey xter:

I just thought of something. I'll have lots of leftover space in my battery box, so I could make an onboard charger out of those things, and just have a 110v ac plug out of my bike. That's the ultimate set-up.

I do have a question: You talk about how you need to watch the voltage while you ride. Why? You can't overcharge the batts while riding.

So is this graphic what you would suggest? If I hard wired the chargers like this, do you think I could ride this way, or would I need to disconnect them?

Thanks for the great tips. I take back all the bad things I said about you. Hub motors rule!!!

 

[Beagle123]

Hi looking:

I'm haven't decided how I'm going to set-up my batteries yet. However, xter has given some great advise. I think we should consider xters point. One advantage to dismantling the battery packs is to save lots of valuable space, and I think his charging method may even be superior to using the stock BMS.

If you look at my situation, I have a huge battery box by ebike standards (11 in X 5.75 in X 7.75in) I figure that I can MAYBE get 8 Milwaukee packs into the space if they fit sideways. If not I can fit only 6. That's 42-56 cells. If I dismantle them, xter and I figure we can use 110 cells.

Obviously keeping the nice neat cases (under warranty) with built in BMS is appealing too.

However, the charging set-up xter describes is really good. It should be very safe, and it will automatically balance the pack. It would have a convenient plug. But also, what alternatives do we have? Unplug each pack and plug it into the charger? I'm planning on 12-16 packs. 12-16 chargers? I could use 8 chargers, and charge half of the packs at a time (not!). As xter said, its unknown if you can wire one charger to two packs and have it work, so you'd then have to take apart each charger and put a plug on it, and plug in all the plugs.

In my situation, my batteries are going to be sealed in a battery box. My only option is to have a plug-in charger. However, jondoah has a nice little bike with 6 batteries that he takes out and plugs into the charger.

By the way, I don't know if you're aware that Milwaukee sells the part that plugs into their battery packs. Jondoah posted about them. Look at his pack. If you really wanted a rack, you could plastic weld them onto a piece of pvc to make a rack.

Hey xter:

I just thought of something. I'll have lots of leftover space in my battery box, so I could make an onboard charger out of those things, and just have a 110v ac plug out of my bike. That's the ultimate set-up.

I do have a question: You talk about how you need to watch the voltage while you ride. Why? You can't overcharge the batts while riding.

So is this graphic what you would suggest? If I hard wired the chargers like this, do you think I could ride this way, or would I need to disconnect them?

Thanks for the great tips. I take back all the bad things I said about you. Hub motors rule!!!

 

[xyster]

Hey xter:

I just thought of something. I'll have lots of leftover space in my battery box, so I could make an onboard charger out of those things, and just have a 110v ac plug out of my bike. That's the ultimate set-up.

That, would rock. Thought about doing that on my bike, but there's no comfortable space. When I build my smaller, lighter emoli "sport" pack later, I'll have the room for chargers. I'm planning on a 92v12ah (23s4p) emoli pack wired as shown in your diagram, and using the same single-cell 1.5A chargers I have now -- I'll just buy three more to make 23.

I do have a question: You talk about how you need to watch the voltage while you ride. Why? You can't overcharge the batts while riding.

True. But obviously you can overdischarge. I destroyed a couple dozen of my lithium cobalt cells during initial testing by discharging farther than I should have. The issue has to do with mega-multicell packs. An individual cell may be spec'd for, say 3.0 volts minimum. But the voltage tanks so fast from 3.60v (the point where capacity is dropping to zero quickly) to 0.0 volts (the point where the cell or subpack goes into reversal and dies permanently) that there's insufficient time to respond in real-world riding conditions. Also, some subpacks are going to be a tad lower than others as the cliff drop-off point is approached, even if balanced on charge. So one subpack will reach polarity-reversal point while the others have enough juice left to push the low pack over the precipice of permanent death. In other words, the bike's pack won't just slowly and safely taper out of energy.
Whether lithium cobalt or manganese, it's best to stop discharge at 3.75 volts (the ~80% DoD point) for long battery life anyway, in addition to preventing the possibility of acute cell death by polarity reversal. Providing a 5% capacity cushion, 3.70 volts (51.8 volts on a 14S pack) is a reasonable "for sure stop and pedal the bike home" point.
LiFePO4 cells (and SLA, and NiMh/Nicad) are not immune to these considerations, their maximum and minimum charge voltages are just lower.
No more distracting than checking the speedo/odo every few minutes or so, monitoring voltage while riding is not a major chore. You just need a single voltmeter showing total pack voltage -- or a device like the CycleAnalyst that shows pack voltage in addition to capacity used. Encouraging efficient throttle control, and ammeter is nice too, but not necessary.

So is this graphic what you would suggest? If I hard wired the chargers like this, do you think I could ride this way, or would I need to disconnect them?

Yes, your diagram is correct. I'd add redundancy and lessen resistance by using two or three wires between the subpacks instead of a single wire -- one on each end and maybe one in the middle of each parallel subpack.

Thanks for the great tips. I take back all the bad things I said about you. Hub motors rule!!!

No prob, Beagle-man. I don't recall any of these bad things you've said about me. Perhaps that's for the best.

 

[miro13car]

Having built 2S3P pack from Milwakee batteries and I am using it for over 800km now I can tell that the way to go is to take batteries out of they cases solder 3 wires - plus, minus and temp probe wire and here you go.
I use AWG12 for minus/plus and AWG18 FOR SENSOR.
By taking them out of their cases you really save room on each otf them - contact blades sticks out pretty high on top of them taking room.
The same charger is used for V18/5 cells/ and V28/7 cells/, it tells you something. for sure charger has programmed charging alogarthm.
If you try to charge 2 V28 in series on one charger, it will take longer, but how do you connect2 sensor wires to one charger?
I carry 2 Miwakee chargers sanwitched together, see my posts /miro13car/ with rotary switches for choosing battery to charge.
MC

 

[Beagle123]

I was just kidding xter.

micro, thanks for the tips. I detailed my plans for my battery pack in my build thread at the bottom. Please take a look and tell me what you think. I haven't read patrick or maytag's threads yet. I'll look for them now. I'm pretty sure I'll prefer xter's method.

I don't know what would best suit you, lookingelectric. If you want to use many batteries, you may want to consider dismantling. IF you're only going to use a few, then jondoah's method is practical.

Have you seen how he did it? Its basicly your idea, but without the rack.

 

[jondoh]

Here are my pictures and new video of how my milwaukee pack goes together. I almost forgot to attach the file.