DIY portable, useful LiFePO4

[markopolo]

LiFePO4 can pack a punch. 3C, 5C? Let's leave fractional C behind for this experiment.

I'm going to try to make an affordable, multi-use portable LiFePO4 pack that actually takes advantage of an extraordinary feature of LiFePO4; multiple C.

I'll post photos of stuff as it arrives from China as I try to put together a portable, useful LiFePO4 pack.

Please point out any errors or any way to do anything better as this topic proceeds.

I'll start with a crimp / solder that went surprisingly well: crimp solder.JPG

6 x 10 AWG into a 1/0 lug. Crimped and soldered.

At the end of this experiment I want an affordable light weight, portable LiFePO4 pack that can power the microwave oven or coffee maker in a Class B van or your home.

[markopolo]

Bluetooth: Yes
User configurable settings: Yes

[markopolo]

Some criteria.
15 lbs or so, easy to carry.

[markopolo]

I'll just mention that I've posted a picture of a dead short on this forum and lived through the embarrassment of that so I really do welcome any comments going forward. I won't be offended and welcome any help and advice as the topic progresses.

[markopolo]

First questions:

Why not multiple C?

Occasionally?

The discharge rate on the the pack I plan to build would be 2 to 3C for those short periods of microwave oven or coffee maker use.

[markopolo]

In case anyone is wondering, those red wires are the same length to the mm.

Yes, I pay attention to what Booster has been teaching us!

[booster]

Interesting idea. Portable so can go from vehicle to vehicle?


How are you going to make the connections to the microwave/host vehicle that is able to handle 100 amps or so?


The greater than 1C discharge rates have long been touted as big plus for lithium, although lately we have heard some chatter that it may not be all that great for them. Certainly nothing that would be considered more than conjecture at this point, though IMO.

[markopolo]

Andersons? Big 120A ones? Need help with that.

[markopolo]

Charge control. If the budget for charge control is $2k then charge control is easy. If the budget is $100 then charge control is a PITA.

[markopolo]

I've placed an order for cylindrical cells and will post specifics if they arrive.

4S10P_Cells_12v_top.jpg

[markopolo]

The size of the battery case I chose doesn't allow multiple built-in options for charge control so I'm forced to go with portable DC to DC chargers (so as not to completely rely on the BMS). Parts coming to build one 20A and one 5A. The 5A was ordered before the project got bigger. I bet LiFePO4 projects often get bigger.

For the 20A unit I'll be stepping 11v to 16V up to 24V then down to do exactly what I want (voltage resolution: 0.01V, current resolution: 0.01A). It's wasteful but the best I can come up with right now for around $100. It's also manual control for the most part. Some automatic charge control is built-in and or planned but, when precise control is wanted, user involvement seems inevitable at this price point.

Both devices could do discharge control if needed. You could charge a lead acid battery bank for example.

I was thinking that a portable LiFePO4 pack could be useful in a B van to power a microwave oven or coffee maker from an inverter while leaving the older 12V system pretty much unchanged.

[markopolo]

Bottom view of pack.


4S10P_Cells_12v_5_bottom.jpg

[GeorgeRa]

Originally Posted by markopolo

LiFePO4 can pack a punch. 3C, 5C? Let's leave fractional C behind for this experiment.

I'm going to try to make an affordable, multi-use portable LiFePO4 pack that actually takes advantage of an extraordinary feature of LiFePO4; multiple C.

I'll post photos of stuff as it arrives from China as I try to put together a portable, useful LiFePO4 pack.

Please point out any errors or any way to do anything better as this topic proceeds.

I'll start with a crimp / solder that went surprisingly well: Attachment 8552

6 x 10 AWG into a 1/0 lug. Crimped and soldered.

At the end of this experiment I want an affordable light weight, portable LiFePO4 pack that can power the microwave oven or coffee maker in a Class B van or your home.

Your method is likely OK. I would do it differently by twisting all wires and use hydraulic crimper. See my connection for 8 and 10 AWG wires.

[markopolo]

A hydraulic crimper would be nice to have. It does make a very good connection. I have the type of crimper that you hit with a maul.

The carry case measures approximately 14" W x 8" H x 4" D. It's going to be a tight fit if I use the cell holders.

case.JPG

4S10P configuration. 40 cells in total. The cells are similar in size to D cell batteries, just a bit taller.

A 32650 LiFePO4 cell measures 32mm x 65mm.

[markopolo]

Initial charging of the individual cells will be handled by tiny charge control modules. I'll have 6 set up & ready to go powered by a spare PC power supply.

tiny charger.jpeg

Link: http://www.consonance-elec.com/pdf/d...SE-CN3058E.pdf

[markopolo]

About the batteries:

I'm hoping that they do a bit better than what this guys testing shows:

https://translate.google.com/transla...-32700-test%2F

I'd like to have 50Ah usable at 80% DOD (at low discharge rates). Fingers crossed.

[markopolo]

A low cost thermostat switch like this - https://www.amazon.com/dp/B0026S6WGK - could keep the battery pack above 32F.

A heater could automatically turn on at 35°F and off at 45°F.

I've tested similar but cheaper switches and have found some variance between them. I'm not sure if I'll add a heater or not though. I had planned to but I'm not sure if it's needed on a portable pack.

[booster]

Originally Posted by markopolo

A low cost thermostat switch like this - https://www.amazon.com/dp/B0026S6WGK - could keep the battery pack above 32F.

A heater could automatically turn on at 35°F and off at 45°F.

I've tested similar but cheaper switches and have found some variance between them. I'm not sure if I'll add a heater or not though. I had planned to but I'm not sure if it's needed on a portable pack.

I also have used and cursed, snap switches in the past, as they would nearly never perform as claimed. Often not in accurate range and even more commonly much wider it on/off range than stated. They are also prone to false trips or pulses from bumps or hits, so might be tough in a portable case. They are mostly used for overtemp shutoffs and such in heating devices, from what I have seen in actual use.


When I did the fan additions to our charging setup in the van, I tried a couple of snap switches without success, as I was sensing air temp and the overly wide range and rating offsets made for poor control. It would either allow the charger to get too hot, or it would not shut off the fans once the air recooled enough.



I wound up using one of the remote temp switch setups for aftermarket vehicle fans. They use a bulb sensor with a tube the switch, which has adjustable an adjusting dial for temp. The on/off range is still a bit high, but is workable for our purpose. They also make a wired sensor version that I have not tested to this point.


https://www.amazon.com/s?k=adjustabl...ref=nb_sb_noss

[Luv2Go]

To more precisely control my heaters, I've used the W1209, along with a snap switch in series with the coil for redundancy. Note this takes power all the time (45ma when off) so it needs to be placed after the BMS switch which will protect the battery from over-discharge.

I have successfully used motorcycle grip heaters for inexpensive heating elements for two installs. YMMV, my boxes are always well-insulated and these heaters are relatively low wattage (about 10W per heater).

The links are to US sellers, if you're willing to wait getting them from China is much cheaper.

[markopolo]

Thanks for the ideas.

If I add a heater, it looks like there is only enough space for a thermostat snap switch (or maybe two snap switches is series). I could add an on/off switch also.

I think the battery will weigh around 18 lbs when all assembled. 3.7lbs already.

150Amp BMS.JPG