LifePO4 GBS Amp Hour Testing 2.5v to 3.6v per cell

[Mike90250]

The simplest method of keeping your pack at the right temperature is to insulate the housing and use a peltier unit to control temps inside. All you need is a peltier and thermostatic controls, we use them where ever a system is going to be subject to varying temps and they are set a between 18-22degC. Peltiers use very little energy when set up properly and provide heat as well as cooling.

Ahh, peltier coolers are about 10% efficient. i'd sure like to be shown otherwise.

[PNjunction]

Took some time off ....

Createthis - re the technomedia RV guy. Just know that this is an amateur where the amount of variables is huge - so take his claims with a grain of salt. He's using those "bleeder boards", who knows if he even cleaned his terminals, and has the right torque on them, and how much damage he caused at the very beginning of his experiment.

I can recommend this canonical video from Prof. Jeffrey Dahn - essentially LFP batteries should last forever, BUT parasitic reactions are what cause them to degrade - aside from up-front damage:

https://www.youtube.com/watch?v=9qi03QawZEk

He's definitely not an amateur! Closer to home, look at videos from Compass Marine about LFP. The same guy also has posted some great articles that you might find of interest:

http://www.pbase.com/mainecruising/lifepo4_on_boats

The thing to remember is to always read the fine print - essentially did the guy START out on the right foot, or was damage caused in the learning process and taken into account when all the fancy amateur charts and advice come out?

Further info can be gleaned from older posts from T1 Terry on various boards around the net, although he seems hard to find these days. Many of just kind of jumped ship and went underground with LFP.

[createthis]

If you were going to run high discharge rates I would put an aluminum plate between each cell in your battery and thermally bond it to something on the side of the battery pack to dissipate heat.

Simon

Not a bad idea.

[createthis]

I can recommend this canonical video from Prof. Jeffrey Dahn - essentially LFP batteries should last forever, BUT parasitic reactions are what cause them to degrade - aside from up-front damage:

https://www.youtube.com/watch?v=9qi03QawZEk

This is a really good video. Thanks.

[J.P.M.]

Not a bad idea.

I'm not as well versed and knowledgeable about batteries as some, but from the little I think I may know about heat transfer, that may not be a very efficient or workable method of heat dissipation. Is it currently done ? If not, I'm not sure how it would be done, but I'd begin by looking at the heat transfer characteristics of the sides of the battery pack. If it is done, then copy or use that design. In my ignorance I'd guess that battery containment surfaces are probably not designed with efficient or high levels of heat transfer in mind, but that may just be my ignorance. How much heat dissipation are we talking here and over what time frame ?

[createthis]

I'm not as well versed and knowledgeable about batteries as some, but from the little I think I may know about heat transfer, that may not be a very efficient or workable method of heat dissipation. Is it currently done ? If not, I'm not sure how it would be done, but I'd begin by looking at the heat transfer characteristics of the sides of the battery pack. If it is done, then copy or use that design. In my ignorance I'd guess that battery containment surfaces are probably not designed with efficient or high levels of heat transfer in mind, but that may just be my ignorance. How much heat dissipation are we talking here and over what time frame ?

I agree. The prismatic cells have plastic housings. Still, there is more surface area between cells than on the sides. Generally though, I'd say the prismatic cells are poorly designed for heat transfer.

[Sunking]

Let's do some math. My cell internal resistances:
Cell 1: 0.00256 ohms
Cell 2: 0.00272 ohms
Cell 3: 0.00288 ohms
Cell 4: 0.00272 ohms

In series, these are added, so 0.01088 ohms total.

V = R * I

V = 0.01088 ohms * 200 amps

V = 2.176

That doesn't seem too bad. 13.2V - 2.176V = 11.024V

So you do not have any problem loosing 16% of your power and your LVD operated at 12 volts, leaving you sitting in the dark?. Have you thought this through? An engineered product would limit losses to 2 to 3% and actually work. You want the maximum sag to be 2%, not 16%

The Ri is so high on those batteries, even a moderate priced 100 AH AGM and some FLA batteries will out perform your batteries at 1/3 to 1/2th the cost and last longer.

FWIW with the Chi-Com cells there is only one way to manage the heat and that is with the Battery Term Post. They are the only thing that can pull heat out of the cell

[Sunking]

The simplest method of keeping your pack at the right temperature is to insulate the housing and use a peltier unit to control temps inside. All you need is a peltier and thermostatic controls, we use them where ever a system is going to be subject to varying temps and they are set a between 18-22degC. Peltiers use very little energy when set up properly and provide heat as well as cooling.

Then all he needs is another set of batteries and panels to run those Peltier coolers .

[J.P.M.]

I agree. The prismatic cells have plastic housings. Still, there is more surface area between cells than on the sides. Generally though, I'd say the prismatic cells are poorly designed for heat transfer.

Since (I'm guessing a bit here) the case is not usually designed primarily as a mechanism of heat transfer, part of my (incomplete) thinking involved getting the heat away from the case after it gets there. If the rate of heat transfer from the case to someplace else (that is, to the surroundings, and probably via thermal radiation) is less than the rate of heat transfer to the case (from the cells), the case temp. will increase until the two rates of heat transfer are equal. That may or may not be a tenable situation. Also, it might not be an easy thing to accomplish in a practical or economic sense. If it was, or is, someone would probably have done it by now, and for all I know, may have.

[Sunking]

If it were me I would put the batteries and equipment in a ventilated steel cabinet

Now there is a really good way to get your arse sued. As stupid as mounting them to aluminum plates and Peltier modules. I bet you stand in water when you work with electricity with both hands tightly gripping your tools.

[createthis]

Yes you are missing something, your LVD operated at 12 volts, and you are sitting in the dark.

Nah. It's programmable:

https://www.victronenergy.com/upload/documents/Manual-Battery-Protect-12V-24V-65-A-100-A--220-A-EN-NL-FR-SE-DE-PT-ES-IT.pdf

[Sunking]

Jesse want to know how DIY EV builders deal with the Heat and Cold? They enclose their cells in a Fiber Glass or Acrylic tanks filled with Mineral Oil or Transmission Fluid. Or if they can get their hands on Transformer Oil.

[Sunking]

Nah. It's programmable:

Are you using an Inverter with its own LVD set to 10.5 volts? What are you going to do when the batteries drop to 13 volts with lots of charge left in you cannot access. What about your cable losses have you accounted for their loss of 2 to 3% on top of the battery sag.

[createthis]

Jesse want to know how DIY EV builders deal with the Heat and Cold? They enclose their cells in a Fiber Glass or Acrylic tanks filled with Mineral Oil or Transmission Fluid. Or if they can get their hands on Transformer Oil.

Like you said before, I think I'm more worried about the cold at this point if it's going to be charging on my covered back porch in winter. Heat can probably be mitigated a number of different ways if I judge it as an issue during operation.

[createthis]

Are you using an Inverter with its own LVD set to 10.5 volts? What are you going to do when the bateries drop to 13 volts with lots of charge left.

Correct: http://www.xantrex.com/documents/Pow...rter%20NA).pdf

It's redundant, but I'll probably only lower the programmable LVD cutoff if I know I'm going to be drawing high loads. Otherwise I can bump it up to something more reasonable.

I don't really care if they've got lots of charge left. Nothing I can do about it, right, short of buying a different battery with lower Ri.