LiFePO4 DIY options

[lfhoward]

Does anyone have recommendations for a good but not too expensive multimeter? My old orange and green Extech is giving all sorts of wild readings. I replaced the battery, which usually makes it better, but this time is isn’t helping. It seems like the main switch that sets the settings is malfunctioning, or there’s some kind of internal short. Occasionally it settles down and gives a solid reading. Currently we are still at 3.31 volts, verified by the power supply when I turn the amps all the way down.

[bdosborn]

Make sure to get the 1.21 gigawatt capacitor, they're the best.
Bruce

[bdosborn]

Does anyone have recommendations for a good but not too expensive multimeter?

Fluke. Pay once, cry once.
Bruce

[Tom&Shelly]

Make sure to get the 1.21 gigawatt capacitor, they're the best.
Bruce

I remember in our undergrad EE classes (early 80's) joking about the 1 farad capacitors we needed to build our filter designs. (Because we normalized our units. Of course we used scientific notation and could take care of the 10^-6 's later.)

I suppose they don't teach scientific notation to engineers anymore, so the youngsters had to actually go and invent a 1 farad capacitor.

Tom

[lfhoward]

^^^ ha ha, I had to look up how much a farad is. That’s a big capacitor for sure. Not sure it is bigger than a 1.21 gigawatt Flux Capacitor though! I’m a biologist not an engineer.

The big news of the day is the battery pack is now up to 3.32 volts. This really is going to take forever, because as the battery voltage approaches the goal voltage of 3.45, the current (amps) will decrease and approach zero. The amperage started out at something like 2.4 amps and now we are down to about 1.8 amps. Charging is slowing down. At some point next week I will have to call it close enough and crank it up to go for 3.65 volts.

[lfhoward]

Does anyone have recommendations for a good but not too expensive multimeter?

Fluke. Pay once, cry once.
Bruce

Seems like everything I need for this project is about $200.

[lfhoward]

I figured out how to mount the BMS to the battery case.

I made a backing plate for it from some aluminum sheet I had left over from the trailer skin.


The BMS has tiny machine screws that were long enough to go through the backing plate, once I countersunk the holes. Then the plate can be screwed directly to the wooden case.


The blue wires will go to battery negative. The black wires will go to the Victron shunt and to the negative bus of the electrical system. I need to make a battery cable to connect the battery positive to the battery shutoff and the positive bus of the electrical system.

[tony.latham]

I’m a biologist not an engineer.

What kind of biologizer?

Tony

[lfhoward]

I’m a biologist not an engineer.

What kind of biologizer?

Tony

Forest Ecologist

[tony.latham]

Forest Ecologist

Gotcha. I used to chase ecology violators. I caught one once. Supposedly.



Tony

[lfhoward]

Re: the slow rate of charge

The battery was getting about 1.5 amps while set to 3.45 volts constant voltage on the power supply. So I turned the setting up to 3.50 volts and the current increased to 2.5 amps. It doesn’t seem like a huge increase but it’s actually 67% more current and this could speed the process up significantly. I will keep an eye on things so the batteries don’t overcharge. When they reach 3.45 volts that’s the time to crank it up to 3.65 and watch the voltage very carefully. At that point we will be only an hour or less away from a full charge. But that could still be days away. The battery is at 3.32 volts right now.

[tony.latham]

When they reach 3.45 volts that’s the time to crank it up to 3.65 and watch...

Is all of this just for the first charge?

Tony

[lfhoward]

When they reach 3.45 volts that’s the time to crank it up to 3.65 and watch...

Is all of this just for the first charge?

Tony

Yes. Some of the people I read talked about a shortcut of charging part of the way with the battery arranged in series using a 12 volt lithium battery charger, then going to parallel for the top balance. Most advocate starting in parallel for the whole charge/top balance sequence but knowing it will take a long time. That’s what I did.

[tony.latham]

Yes.

Thanks for the explanation. Me? I'm assembling fishing (and camping) gear. We have to go chase some westslopes.



Tony

[lfhoward]

Yes.

Thanks for the explanation. Me? I'm assembling fishing (and camping) gear. We have to go chase some westslopes.



Tony

Fishing and camping sound good! Hope it’s a good trip. Are you under that western heat dome?