38120 Project

B

Badblue

New member
Joined
Jan 25, 2018
Messages
27
Hi all,

I just picked up 32 Headway 38120 cells and I'm looking for project ideas.

I've always wanted to build a powerwall that eliminates peak and mid-peak rates and only recharges during off-peak hours. My house only has a 60A service using 1600kWh a month.

My truck has several amps and subs that devour lead acid batteries. I have a big cap that helps ... but it also self discharges over time ... so the truck needs to run every few days to keep the battery healthy.

I built an electric atv that is underwhelming. 800W DCmotor @30A powered by 4x36Vhoverboard packs is just not enough to have real fun. Perhaps a 1/3HP AC motor on an inverter would spice things up?

Apparently, these cells are many times more powerful than the familiar 18650s. One of the main reasons I bought these is their voltage allows friendly use in12V and 24V systems.

I'd love to hear the communities thoughts on these cells and what these are capable of.

Here are the specs:

chemical composition

LiFePO4​

Nominal Capacity​

8Ah​

Charging voltage​

3.65V​

Nominal Voltage​

3.2V​

Cut-off Discharge Voltage​

2.0V​

Charging Method​

CC/CV​

Maximum Discharge Current(continuable)​

200A​

Maximum Charge Current(continuable)​

80A​

Cycle Life​

1500cycles 1C 100%DOD​

2000cycles 1C 80%DOD​

Work temperature​

Charge -10?to 45?​

Discharge -20?to 65?​

Energy Density​

83 Wh/Kg​

Initial Internal Impedance​

<4m?​

Dimension(mm)​

Diameter​

38mm​

Length​

120mm(152 with screw)​

Weight(g)​

360
 
Nice I'm currently doing something similar with my wall. I have a daily Average of 20kWh and Peak and Mid ammounts are usually within the 4-7kWh. I have a 1500VA APC that is just over 1000W capable inverter built in. I have moved my fridge, freezer and Internet/ computers onto my Power Wall. still in testing mode right now and it seems to be working. the internal battery charger only outputs 5Amps so I cannot use my full power wall so I'm looking for adjustable 24v Power Supply in the 30+ Amp range.

Sounds like a fun project.
 
jdeadman said:
Nice I'm currently doing something similar with my wall. I have a daily Average of 20kWh and Peak and Mid ammounts are usually within the 4-7kWh. I have a 1500VA APC that is just over 1000W capable inverter built in. I have moved my fridge, freezer and Internet/ computers onto my Power Wall. still in testing mode right now and it seems to be working. the internal battery charger only outputs 5Amps so I cannot use my full power wall so I'm looking for adjustable 24v Power Supply in the 30+ Amp range.

Sounds like a fun project.
Click to expand...

My thoughts are to use my 60A service to power a 24V charger which is ona timer set for off-peak hrs. I'll have to use a very large 24V dual 110/220Vinverter which couldbe wired directly to a100A breaker panel.In this case, the batteries would power the entire house 24/7. I have not calculated anything yet. I'm not confident in my battery maths yet.
 
That's a good plan. i've just been playing with what I have/find for cheap or free.99 With calculating your loads I look up the watts or Amps each devices takes. Then collect them together based on, Constant, Occasional, or High Load.

then normalize all of your loads into Watts. if Amps @120V Just multiply the numbers to get watts eg. 120@ 2A = 240W Now that's just for the AC side. remembering you have losses when calculating your DC side just add about 5% to the numbers when Done.

In choosing your DC voltage you have lots of options, 12V, 24V, 36V, 48V and 60V. This choice is the biggest thing to think about. The lower the Voltage the higher the Amps therefore the bigger the DC cables need to be.

eg, total max current on the AC side would be 35A = 4200W or 4.2kW

Current from the batteries would be :4200+5% = 4410

12V = 4410/12 = 368A
24V = 184A
36v = 123A
48V = 92A
60V = 74A

Now you can see the Amp load goes way down the Higher the Voltage.


The cost of the Inverters needed are pretty high but a guy on youtube GoingOffgrid has been using reliable branded Cheap inverters up to 8kW with some sucess and some failures. Check out his channel as he's also from Southern Ontario.
 
Its time for me to start a project. I have a bit of time off, so there's no time like the present.

I estimated my maximum loads for my entire home using a generator sizing calculator.


image_funyrn.jpg


I currently only have a 60amp service. I have blown one of my main fuses on occasion in the past when using the dryer AND range, plus the A/C and possibly the hot tub kicking in to cycle. So this calculator seems fairly accurate and a little forgivingat 73amps max draw.

My goal is to never pay for peak power again. So I'm looking to power my home for 10-12 hours during the day with the possibility of adding solar panels in the future.

I have 32 LiFePO4 cells @3.2V/200A that can charge at up to 80A. So I'll have to decide on the pack design. I have a 3d printer to make my cell holders.

Now, I'd like to start sourcing my 120/240 inverter/charger. I'd like it to have an automatic transition switch between grid and battery. However, I can't imagine having to use a 17kw inverter. What size inverter should I be looking at? I assume that I should be using a pure sign wave inverter vs a modified one as well.

Any suggestions or recommendations?
 
This is one model I was looking at. Seems to check all the right boxes for my requirements. Although, I don't know if 10kw is overkill or not.
10kW Inverter Charger

This model is one that GoingOffGrid (Thanks jdeadman)was testing. It's half the price ... but might be half the quality too!
15kW Inverter Charger

It seems to me that I might be able to use a decent 8000W inverter, but this is not my strong point. I'm a better builder than a designer.
 
If you have access to your online usage. You should be able to see daily draws by the hour. Have a look at the max draw for any hour in the last year. that will be for sizing your inverter. For me my worst hour is almost 7kW, that was furnace, stove dryer and Black heater in the car plugged in. Now you can manage your loads manually to keep the usage down to get a cheaper inverter. but that's what I'd start with. If you can only see Daily and not hourly then just devide the total used for that day by 10 (why 8? since at night there is minimal usage and what you are looking for is your highest draw at any one time)

this will get you in the ball park. My highest day was 55kWh 55/8 = 6.875 which is pretty close to my max draw

So I would start looking for a 8kW inverter or 2x 4kWh and split my big loads up

Yea or Go big and never worry. lol No Prob.

And blowing a 60A fuse I would say you were pulling closer to 70Amps so that would work out to 8400W or 8.4kW But Again you could mitigate that by manually controlling when your big loads come on etc.
 
It took me a long time to decide what to build. Then my truck needed an $8400 engine rebuild. When I was told it would be another $400 for a battery I knew what I had to do.

This is my first model. It is printed with PLA. I will make another out of ASA and use this one as an in-cab amp battery and emergencybackup.


image_ainyce.jpg
 
Nice battery. and Way more than enough Power
 
jehugarcia just posted a video on youtube and used my custom builtbattery picture at 1:27 into the video.

Check it out here


Got to be honest, got a bit of a semi going on right now ... LOL
 
That video is a week old and almost started an international incident with "deleting posts that weren't in accord with the rules" issue. :p

But, aside from that, is nice when large channel broadcasters post/mention/show your small project you've been working on ;)
 
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