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Old 02-14-2016, 09:34 AM   #15
George
 
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Very interesting. What is the major advantage you expect? The power (200 Ah) seems about the same as 2 Lifeline AGM's, but maximum discharge rate (2 kW) a bit higher.
Do you expect major weight savings?

Thanks!
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Old 02-14-2016, 03:37 PM   #16
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Step #1:
Caution: This is the most challenging step, it only takes about an hour to accomplish, take your time, measure the cut location with a voltmeter and then mark the cuts. I put a (+) and (-) on the sides of the cut to show the polarity of the results. Use a hot knife or soldering iron to cut the plastic back so you can see the full length of the cut. Then try to only cut the copper bar, there is a small space under the bar, if the cut is too deep the cutter will hit the top of the cell.

First image shows the 48VDC battery. Second image show 12 VDC from the ground lug to the first strap to cut. By moving the negative voltmeter lead to the 12VDC node the positive voltmeter lead can be used to find the next strap to cut. Repeat again for the third and last cut. I marked the three straps and verified each of the four sets would make 12VDC.





I have two cutting tools one is a vibratory nice and small easy to reach in makes a nice cut. The second is a rotary with a 5" wheel, a 3" wheel would be better. I used both machines to show that they would both do the job, a Dremel would likely work too as long as you can reach the cut. The depth needs to be controlled the smaller tools is easier to keep from going too deep. Cutting a small amount of plastic is OK, just don't get into the center section it has a bunch of connecting wires. A utility knife can be used to cleanup any leftovers metal parts. I found that a soldering iron would cut the black plastic back to expose the full length of metal to cut. Here are pictures of the three cuts:









This one was cut by 5" wheel:


Installing the cable I can measure the voltage from the 4 pin BMS connector to ground. I found 3 cell voltage (12VDC), 2 cell voltage (8VDC) and 1 cell voltage (4VDC). This is the setup for the first series of cells starting at the ground lug. So far everything is cut/wired correctly and ready for the next step.



The next step will be to connect the other three 12VDC batteries. I will also use some non flowing epoxy in the cut to keep the circuit open. I will wire the battery system so that I can check the effectiveness of the BMS. More effort that just wiring all the +12VDC together, but I want to be sure that the batteries stay balanced as claimed by the seller. The logic the seller is applying is that balancing 288 cells is necessary, balancing four sets of 3 cells is not.

There was a question about weight savings. This battery weighs 40 pounds.
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Old 02-14-2016, 07:05 PM   #17
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Originally Posted by gwmc View Post
Very interesting. What is the major advantage you expect? The power (200 Ah) seems about the same as 2 Lifeline AGM's, but maximum discharge rate (2 kW) a bit higher.
Do you expect major weight savings?

Thanks!
Two Lifeline AGM's will only provide 100aH as they can only be drawn down 50% safely without shorting lifespan. Lithiums can be drawn down 80~90% depending on type and except bulk charge all the way to full which means they can recharge at a faster rate. They also don't need to be fully charged to start discharging unlike Lead Acid. Other advantages abound; such as great number of cycles within the lifespan.
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Old 02-14-2016, 07:08 PM   #18
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Originally Posted by sgschwend View Post
Step #1:
Caution: This is the most challenging step, it only takes about an hour to accomplish, take your time, measure the cut location with a voltmeter and then mark the cuts. I put a (+) and (-) on the sides of the cut to show the polarity of the results. Use a hot knife or soldering iron to cut the plastic back so you can see the full length of the cut. Then try to only cut the copper bar, there is a small space under the bar, if the cut is too deep the cutter will hit the top of the cell.

First image shows the 48VDC battery. Second image show 12 VDC from the ground lug to the first strap to cut. By moving the negative voltmeter lead to the 12VDC node the positive voltmeter lead can be used to find the next strap to cut. Repeat again for the third and last cut. I marked the three straps and verified each of the four sets would make 12VDC.





I have two cutting tools one is a vibratory nice and small easy to reach in makes a nice cut. The second is a rotary with a 5" wheel, a 3" wheel would be better. I used both machines to show that they would both do the job, a Dremel would likely work too as long as you can reach the cut. The depth needs to be controlled the smaller tools is easier to keep from going too deep. Cutting a small amount of plastic is OK, just don't get into the center section it has a bunch of connecting wires. A utility knife can be used to cleanup any leftovers metal parts. I found that a soldering iron would cut the black plastic back to expose the full length of metal to cut. Here are pictures of the three cuts:









This one was cut by 5" wheel:


Installing the cable I can measure the voltage from the 4 pin BMS connector to ground. I found 3 cell voltage (12VDC), 2 cell voltage (8VDC) and 1 cell voltage (4VDC). This is the setup for the first series of cells starting at the ground lug. So far everything is cut/wired correctly and ready for the next step.



The next step will be to connect the other three 12VDC batteries. I will also use some non flowing epoxy in the cut to keep the circuit open. I will wire the battery system so that I can check the effectiveness of the BMS. More effort that just wiring all the +12VDC together, but I want to be sure that the batteries stay balanced as claimed by the seller. The logic the seller is applying is that balancing 288 cells is necessary, balancing four sets of 3 cells is not.

There was a question about weight savings. This battery weighs 40 pounds.
Looks awesome! This is some serious DIY. I considered briefly taking apart a Tesla battery pack which is made up of dozens of 18650 cells. And then soldering them together. But I chose the easier route.
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Old 02-15-2016, 02:33 AM   #19
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This is very interesting project indeed! I'm currently building a 4 x 2.5kW setup using four MasterVolt's 180 Ah batteries - ie, total of 720 Ah of li-ion-power. However, my setup is much, much more expensive.

http://www.mastervolt.com/products/l...ultra-12-2500/
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Old 02-15-2016, 04:53 AM   #20
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Best wishes on your experiment. You could create a mass of followers!

Quote:
n exploding batteries, these Li-ion batteries used in the EV community and now being used in RV's are not the same chemistry. EV battery cells are generally tested for on road use, which requires the cell not to catch fire or explode when dropped, over discharged, overcharged, baked, frozen, crushed or pierced with a steel rod.
Yeah, except that the REAL issue isn't the battery as much as it is the charging system. Apparently they are very sensitive to how charging is done:

"While the traditional lithium-ion has a nominal cell voltage of 3.60V, Li-phosphate (LiFePO) makes an exception with a nominal cell voltage of 3.20V and charging to 3.65V. Relatively new is the Li-titanate (LTO) with a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Types of Lithium-ion.)

Chargers for these non-cobalt-based Li-ion are not compatible with regular 3.60-volt Li-ion. Provision must be made to identify the correct systems and provide charging with the correct voltage. A 3.60-volt lithium battery in a charger designed for Li-phosphate would not receive sufficient charge; a Li-phosphate in a regular charger would cause overcharge."

http://batteryuniversity.com/learn/a..._ion_batteries
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Old 02-15-2016, 09:13 AM   #21
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Yes BoldA. this new chemistry has a lot to offer in power, and the automotive battery is very rugged.

I have been studying the BMS. It has to be able to setup for this charge/operation range. Remember there is both an upper and lower limit. I feel I paid an extra $100 for the programming of the BMS. My seller tells me that the part I have has a memory chip that supports changing the values of the upper and lower limit. The board can handle up to 30 amp of DC charging, my plan is to use the board to control a relay so it will only need to switch a fraction of an ampere. Less stress on the board that way.

I am also looking at purchasing a different BMS so that I can monitor all twelve cells and run balance charging, even though the seller tells me this is a waste of time. He has worked in this area for many years. His work includes the rebuilding several electric vehicles for his customers so his knowledge goes beyond purchasing and selling batteries. His operation shows the obvious signs of success.

As this project goes on you will be able to see how my seller's solutions is accomplished along with some added accessories and electrical tests. The seller will sell the battery and parts individually or a completed 12VDC battery assembly. Again I recommend folks wait and see how this goes and compare the final cost. My cost will be higher because of the messing around but the next builder will be able to save. My current guess is that battery, battery cover and cable/connectors but not the BMS will cost $600. BMS or the size I purchased were less than $20.
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Old 02-15-2016, 09:30 AM   #22
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Step #2 Wiring the four cell sets together.
My seller uses 12ga solid wire, he runs the wire from the farthest connection back to the terminal lug. He then runs two shorter wires to intersect the first wire. My guess is that he uses a large soldering iron (100 American Beauty) and solders everything together.

This would not pass mil spec. but given the rigidity of all those metal tabs it is not that bad. His last step is to cut clearance under the cover for the wire runs. The easiest way to do this is to use the soldering iron and just melt the places that need changing.

I will do this a little differently, I will be drilling a hole in the vertical cell tabs/lugs so I can mechanically hold the wire before soldering. I can make great solder joints but others that are following this process might not and the mechanical connection will keep folks from getting into trouble. For eight 1/8" holes the wires will stay put.

see the next post for the results. (materials: epoxy, wire, terminal ends and solder, tools: soldering iron, wire strippers, needle-nose pliers)

I am looking at the Mastervolt web page now. Looks good, I like that they share information and prices!
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Old 02-15-2016, 09:57 AM   #23
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my plan is to use the board to control a relay so it will only need to switch a fraction of an ampere. Less stress on the board that way.
This may or may not be of help. My BMS has two sources of 12v for an Over Voltage alarm and Under Voltage alarm. Both sources will go to ground if an alarm sounds for OV or UV. I use those to control a solenoid via two relays. If an alarm happens, the solenoid opens removing the battery from the system.

Here is how I wired this



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Old 02-15-2016, 06:28 PM   #24
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Quote:
Originally Posted by sgschwend View Post

I am also looking at purchasing a different BMS so that I can monitor all twelve cells and run balance charging, even though the seller tells me this is a waste of time. He has worked in this area for many years. His work includes the rebuilding several electric vehicles for his customers so his knowledge goes beyond purchasing and selling batteries. His operation shows the obvious signs of success.
sgschwend,

Looking good so far!
See link here to the AM Solar lithium battery document that gives some useful information on how to configure the BMS boards on the battery with various parallel and series arrangements. Looks like they provide 4 BMS boards (not one per cell) and have various battery configurations shown with BMS board locations. They also describe how to set up a couple of different chargers (both configurable) for their LiFePO batteries.

I'm particularly interested in seeing the BMS the vendor provided plus how you plan to do it.

Any thoughts about low ambient issues? I see that most Li Ion chemistry should not be charged below 0C and not discharged below -20C. My interior mounted AGM's were sitting at -10C this weekend (float charging by solar) and only came up to about 0C after 4 hours of running the furnace and an interior temp of 50C. Electric heating pads under the batteries seem to be the preferred option.
Wonder how they handle that in the car? There are ducts down each side - is that for air or water?
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Old 02-15-2016, 07:16 PM   #25
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Step #2: Wire the four 12VDC batteries together.
I have a paste type of epoxy, it will not move and dries hard. I placed it inside the saw cuts to ensure the cuts would stay open.



I then tried to drill holes in the tabs so I could wrap the wire around the tab. I found the drill was at about a 30 degree angle and I would need to make a drill fixture out of non-electrically conductive material in order for the drill to work. Rejecting this idea I will just solder the wires as recommended to show the next DIY guy what to do.

Here are my tools: The 100W American soldering iron, hand torch, IR thermometer.

My soldering iron element reaches 340 C which is enough temperture, but my iron tip was only at 240C. This is not going to be hot enough to solder those copper tabs. So I shot the end of the iron with the torch for a count of 5 seconds. With the extra heat I could pretinned each connection point with solder. This way I know I have a soldering site and I can hold the pretinned wire to that soldering site and solder the wire to the tab.

Final assembly, then the top placed, connector installed and here it it with charger running.

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Old 02-15-2016, 07:43 PM   #26
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Now for testing and looking for a simple set of gauges that can measure consumption and state of charge.

As to the question about this particular BMS. The BMS I am using will balance three cells so that the three cells reach full charge at the same time.

We just need to understand that the three cells that make the 12VDC are actually four groups of three series connected. The easy way to think about all of this is that the 12VDC battery is three cells, and the BMS (battery management system) is programmed to charge and protect a three cell 12VDC battery.

The consequence of our trailers using a low DC voltage of 12VDC. Ideally 48VDC would be a better voltage to use, the wires could be smaller, the 12 cells could be in series and each cell could be monitored and balanced.

My current thinking is to add a power meter to allow the monitoring of battery both in charging and in load. User could then keep track of the system performance and this would indicate if the battery is OK. The method would be to fully charge the battery then see how many AH the charged battery produces. It should produce the same energy every time.
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Old 02-16-2016, 02:26 PM   #27
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sgschwend, can you post the exact outside dimensions of the 48V battery?

I found a seller, Al, on eBay who sells these new. The guy is in Livermore and is quite a character. Is this the same seller?

He has a 72V pack, which can be modified to 12V with a capacity of 300 AH for $848 (unmodified pack). He says the cell is a combination of the 48V and 24V pack.

He's pretty adamant that the individual cells in series are not actively managed by a BMS in the Chevy Volt. For example, for the 48 V battery, the configuration is 12S where each 3S (three series connected cells) is actively managed by the BMS. When the 48 V pack is modified to 3S4P (three series cells, paralleled four times), only undervoltage and overvoltage protection is required. In the case of the 72V pack, the configuration is 3S6P. All this according to Al.

He also mentioned that the pack can be placed in any orientation.

Again thanks for the DIY and I look forward to your progress.
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Old 02-16-2016, 04:06 PM   #28
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I made a mistake. The 48V Chevy Volt packs are configured as 3P4S (meaning three cells in parallel are then connected in series four times). This means that the Chevy BMS is probably monitoring and balancing each set of three.

So sgschwend, is your BMS going to balance each parallel set of three? Or is your BMS just going to monitor the output terminals for undervoltage and undervoltage? I got the impression after speaking with Al that it's not necessary to balance each set of three but I'm not sure I buy it. What's your opinion?
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