Budget Bottom Balancing

Using a LightObject 5740 Volt Meter to build a $100 LiFePO4 bottom balancer

You will need a wall wart power supply, a power resistor, a high amperage continuous duty relay, a LightObject 5740 volt meter, a pair of 30A alligator clips, a pair of smaller alligator clips, some 8 or 10 gauge wire, and some small gauge wire.

Major components:
Wall wart power supply 16vdc 5w $10
http://www.digikey.com/product-detail/en/DA4-165US/454-1400-ND
.1 Ohm 200W resistor $28
http://www.digikey.com/product-detail/en/2-1630019-7/A102386-ND/
Continuous Duty Solenoid 80AMP 12V $16.50
http://www.amazon.com/Continuous-Duty-Solenoid-80AMP-12V/dp/B0050I94XG
Programmable 4 Digit Red LED AC/DC Volt Meter with dual control. $38
http://www.lightobject.com/Programmable-4-Digit-Red-LED-ACDC-Volt-Meter-with-dual-control-Good-for-HHO-System-P408.aspx

I built mine for considerably less than $100, I had everything except for the 5740 meter. I used a wall wart power supply left over from a dead router, several 0.1 Ohm 20W power resistors that I ganged together, and a contactor that will eventually go on my motorcycle pack.

It isn't very pretty, but it works. The resistors that I had, when connected 5P2S across a LiFePO4 cell, draw about 40A. The power resistor listed above from Digikey draws about 20A.

Below I have a JLD404 hooked up with a shunt to show the 40.5A draw at 3.24v with my resistors. I'm going to have to get some heavier wire to connect my resistors... 40A was making them get warm. A fan blowing across the resistors and wires helped a lot. I probably should add a fuse or two in there somewhere.

Here you can see where I rebuilt the balancer with the power resistor, better wires, alligator clips, and a fuse on the power lead. The JLD404 shows that it is drawing 22.7A at 3.27v. This power draw is closer to the recommended 0.3C discharge for the cell. 

Wiring the balancer:

1. Connect your dc power supply to terminals 1 and 2.

2. Jumper terminal 1 and 15 to connect the positive DC power to the common terminal (15) of J1.

3. Connect one side of the contactor to the normal closed terminal (14) of J1.

4. Connect the other side of the contactor to negative DC power (terminal 2).

5. Connect the negative voltage sense lead to the COM terminal (8).

6. Connect the positive voltage sense lead to the 10V terminal (6).

7. Connect one side of the contactor power terminal to the power resistor with heavy wire.

8. Connect the other side of the contactor to a heavy alligator clip with heavy wire.

9. Connect the other side of the power resistor to a heavy alligator clip with heavy wire and a 12V/30A fuse.

Programming the balancer:

1. Press Manual/Enter and enter 0001 to get the relay menu.

2. Set AH1, the high voltage trigger, to your lower voltage (2.60v).

3. Set AL1, the low voltage trigger, to your higher voltage (2.75v).

4. Select End and press Manual/Enter to exit the relay menu.

5. Press Manual/Enter and enter 0036 to get to the configuration menu.

6. Set PuL to 0.000 for no offset
7. Set PuH to 1.000 for displaying 0.000 to 9.999 vdc.

8. Set dot to 3 for 3 decimal points.

9. Set FILt to 0 for no noise filtering.

10. Select End and press Manual/Enter to exit the configuration menu.

When the voltage is higher than 2.75v the contractor will energize, drawing power from the cell. When the voltage gets down to 2.60v, the contractor will open, removing the load. If the voltage rises above 2.75v, it will close again. After several cycles, the voltage should settle just below the 2.75v.

Homebrew EVSE

One of the guys at the Dallas Makerspace has a Tesla Roadster so he decided that he needs an EVSE at DMS as well as at home. It uses an EVSE controller from the Open EVSE Project, a pair of solid state relays, terminal strips, 12v psu, panel box, and a J1772 cable/connector. He did an Instructable on it.

Below is a shot of it mounted next to the warehouse door. It normally has the lid to the box in place for safety.

CALB CA60FI spec sheet

Testing update

I've tested about one third of my cells, and all of them so far are in excess of 60Ah capacity. The cells come from CALB at about 50% charge, the PowerLab 6 takes about 6 hours to charge from half to full, discharge and recharge.

Below are some graphs that the PowerLab spits out, the raw data is also available, so I plan to look at the stats when I'm done testing the entire set.

Here you can see that the PowerLab puts in a little over 30Ahs, rests for 15 minutes, removes a little over 62Ahs, waits for 15 minutes, then puts back in a little over 63Ahs.

Here you can see the steep "knee" as the cell gets full, the plateau as the charger changes from constant current to constant voltage mode at 3.60v, the drop as the surface charge dissipates during the 15 minute cool down. Then we see the sharp drop as a 30A load is applied and the slow drop until the steep knee as the cell approaches empty, and a quick recovery as the load is removed at 2.80v for another 15 minute cool down period. In the final phase, we see a steep curve as charging starts at 30A constant current, then a long fairly flat charging curve and another steep knee as the cell gets full again, followed by the constant voltage plateau to finish.

The CALB paperwork lists this cells internal resistance as 0.44 mOhm. The PowerLab measured it at 0.5 mOhm. The other cells have been similarly off, and similarly flat on the graph. I'm not sure what that means, if anything.

More Power Parts

The hardware for the cells showed up, the bolts seem to be fairly good stainless steel, as are the flat and split washers. The battery interconnects are several thin sheets of copper stacked and heat shrinked together.

I don't like split washers in things that vibrate... like motorcycles, so I ordered some Nord-Lock washers.

I also ordered a JLD404 and shunt from LightObject. I'm not sure where I'm going to mount it yet.

Testing

I ordered a Revolectrix Powerlab 6 to test my cells.

Finally...

I've been busy, and not on fun stuff like the motorcycle. I've finally got some time to get back to work on the bike and ordered some batteries.

I really, really wanted to get Sinopoly LFP60AHA(B) cells, and got some good quotes from Sinopoly, but just couldn't get a reasonable solution to importing and shipping them to Dallas. I ended up getting the new CALB CA60FI cells from Keegan at http://www.calibpower.com/

They arrived UPS Freight in two small crates shrink-wrapped on a pallet. I removed all the extra packing material and consolidated them down to one small crate for storage while I'm working.

Unfortunately, they neglected to ship the bus bars and bolts with the batteries, so I'm waiting on those to show up in the next day or two.

I ordered 48 cells, and plan on installing the best matched 36 of those in the bike. The other 12 will be used on various other projects. I'll update on the testing soon.

According to the CALB paperwork they all tested 65Ah to 67Ah. Two were 65Ah, 25 were 66Ah and 21 were 67Ah. The "Open Circuit Voltage" listed was 3.304v or 3.305v for 45 cells with two more at 3.306v and one at 3.309v.