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LiFePO4 Batteries: Discussion Thread
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jimf909 Premium Member
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PostPosted: Wed Jul 14, 2021 9:44 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

This was a superb read. Thank you. I need to leave the vanagon cul de sac more often.

xoo00oox wrote:
Thanks guys! I don't want to muddy up the waters in this thread too much, here is the boat in the back of my van, it is a Glen-L Squirt I am just finishing up. I am using an Epropulsion Navy 6.0 outboard.

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You can read about it here in the Glen-L forum..

http://www.glen-l.com/phpBB2/viewtopic.php?f=17&t=35956

and here in the off-topic section of Samba.., there is a YouTube video of my daughter and I driving it at the end.
https://www.thesamba.com/vw/forum/viewtopic.php?t=749312[/img]

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Current: 1990 Westy Camper - Bostig RG4, 2wd, manual trans w/Peloquin, NAHT high-top, 280 ah LFP battery, 160 watts solar, Flash Silver, seam rust, bondo, etc., etc.

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PostPosted: Thu Jul 15, 2021 5:50 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

xoo00oox wrote:
Howesight-thanks for the tips. I do agree with you, it would be better to have a thin plastic insulator between each cell. I’m planning on getting sheets of ABS plastic from McMaster. I really just put this box together quickly because I wanted something to hold them while I tested them.

FXR- thanks for the tip but there are no BBB around me.


This is what I used from Amazon.

https://smile.amazon.com/gp/product/B08FY6RD46/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
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PostPosted: Thu Jul 15, 2021 10:37 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

dobryan wrote:
xoo00oox wrote:
Howesight-thanks for the tips. I do agree with you, it would be better to have a thin plastic insulator between each cell. I’m planning on getting sheets of ABS plastic from McMaster. I really just put this box together quickly because I wanted something to hold them while I tested them.

FXR- thanks for the tip but there are no BBB around me.


This is what I used from Amazon.

https://smile.amazon.com/gp/product/B08FY6RD46/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1


Agree on these cutting boards. I got mine at the dollar store where they also had placemats from the same material. Thinner than the cutting boards. Scraps of plywood on each end with long hose clamps to tighten together. Cheap, not so pretty, but effective.
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fxr
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PostPosted: Fri Jul 16, 2021 3:37 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

I am very disappointed in the SOC (State of Charge) estimations of the Overkill BMS. It seems it makes its guess from the voltage readings, NOT from integrating the current flow in and out. Sad It keeps a record of the voltage, current and SOC guesstimates - I'm sure the firmware developers could have made use of its current measurements for the SOC.

I am hesitant to outlay another $40 - $60 just for an SOC meter. Sad

What do other BMSs do in the real world, as opposed to their descriptions?
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PostPosted: Tue Jul 20, 2021 7:21 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

For those who put the batteries in the driver's box, what did you do with the blue wire that's 14v when engine on and the red wire that's from the fuse panel by way of the starter battery
Also, how did you run your 8 or 6 awg wire from starter battery to the DCDC chargers?
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PostPosted: Tue Jul 20, 2021 11:45 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

fxr wrote:
I am very disappointed in the SOC (State of Charge) estimations of the Overkill BMS. It seems it makes its guess from the voltage readings, NOT from integrating the current flow in and out. Sad It keeps a record of the voltage, current and SOC guesstimates - I'm sure the firmware developers could have made use of its current measurements for the SOC.

I am hesitant to outlay another $40 - $60 just for an SOC meter. Sad

What do other BMSs do in the real world, as opposed to their descriptions?


This is common. Most inexpensive BMS do what you describe. You need a shunt battery monitor. You can pay a lot and buy a Victron, or buy one of the many Chinese versions that work just fine as well for around the price you already mentioned. I have bought from both Amazon and aliexpress and lean towards Amazon these days as there isn't much price difference. The BMS doesn't count Coulombs and that's what is needed.
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PostPosted: Wed Jul 21, 2021 8:38 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

Thanks for the confirmation. I ordered a cheapo coulomb counter yesterday. Smile
$20 inc postage from China. Huge long link:
https://www.banggood.com/PZEM-015-Battery-Tester-D...02448.html
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PostPosted: Wed Jul 21, 2021 9:57 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

fxr wrote:
Thanks for the confirmation. I ordered a cheapo coulomb counter yesterday. Smile
$20 inc postage from China. Huge long link:
https://www.banggood.com/PZEM-015-Battery-Tester-D...02448.html


Oh boy. Sorry for this. And just when I thought I had things figured out.

I thought the purpose of the bms was to measure the condition of each individual battery in the series to prevent under charge, temp and over charge?

Are you buy four of the coulomb counters to “monitor” the individual flow into or out of the individual batteries? Will you also have a bms? Why? Thanks in advance.
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PostPosted: Wed Jul 21, 2021 11:17 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

rmcd wrote:
fxr wrote:
Thanks for the confirmation. I ordered a cheapo coulomb counter yesterday. Smile
$20 inc postage from China. Huge long link:
https://www.banggood.com/PZEM-015-Battery-Tester-D...02448.html


Oh boy. Sorry for this. And just when I thought I had things figured out.

I thought the purpose of the bms was to measure the condition of each individual battery in the series to prevent under charge, temp and over charge?

Are you buy four of the coulomb counters to “monitor” the individual flow into or out of the individual batteries? Will you also have a bms? Why? Thanks in advance.


You use one coulombmeter per battery or set of batteries. A battery can be 4 - 3.2v cells for 12.8v which most of us use. You can do a 24v battery with 8 cells or a 48v with 16 cells. These numbers all refer to LiFePO4 cells. I use the 48v for my house and the 12v for my Syncro. I used to run two 100ah batteries in parallel in the van with one coulombmeter. Each battery had a BMS though. Currently (see what I did there?) I have a homemade 240ah single battery with a JBD 120a BMS with bluetooth and low temp protection and a generic Chinese coulombmeter.
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PostPosted: Thu Jul 22, 2021 9:16 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

rmcd wrote:
fxr wrote:
Thanks for the confirmation. I ordered a cheapo coulomb counter yesterday. Smile
$20 inc postage from China. Huge long link:
https://www.banggood.com/PZEM-015-Battery-Tester-D...02448.html


Oh boy. Sorry for this. And just when I thought I had things figured out.

I thought the purpose of the bms was to measure the condition of each individual battery in the series to prevent under charge, temp and over charge?

Are you buy four of the coulomb counters to “monitor” the individual flow into or out of the individual batteries? Will you also have a bms? Why? Thanks in advance.

The coulomb counter (SOC meter) is for the whole battery, not the individual cells. The BMS does a fine job of monitoring and protecting the cells, but doesn't give a usable State Of Charge estimate for the whole battery. (0% to 100%)

So just one of these SOC meters is required for the aux battery.
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PostPosted: Thu Jul 22, 2021 9:32 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

gtinseth wrote:
fxr wrote:
I am very disappointed in the SOC (State of Charge) estimations of the Overkill BMS. It seems it makes its guess from the voltage readings, NOT from integrating the current flow in and out. Sad It keeps a record of the voltage, current and SOC guesstimates - I'm sure the firmware developers could have made use of its current measurements for the SOC.

I am hesitant to outlay another $40 - $60 just for an SOC meter. Sad

What do other BMSs do in the real world, as opposed to their descriptions?


This is common. Most inexpensive BMS do what you describe. You need a shunt battery monitor. You can pay a lot and buy a Victron, or buy one of the many Chinese versions that work just fine as well for around the price you already mentioned. I have bought from both Amazon and aliexpress and lean towards Amazon these days as there isn't much price difference. The BMS doesn't count Coulombs and that's what is needed.


Interesting topic on DIYsolar.

https://diysolarforum.com/threads/accuracy-of-overkill-bms-soc.20354/
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'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794
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PostPosted: Thu Jul 22, 2021 12:16 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

dobryan wrote:
gtinseth wrote:
fxr wrote:
I am very disappointed in the SOC (State of Charge) estimations of the Overkill BMS. It seems it makes its guess from the voltage readings, NOT from integrating the current flow in and out. Sad It keeps a record of the voltage, current and SOC guesstimates - I'm sure the firmware developers could have made use of its current measurements for the SOC.

I am hesitant to outlay another $40 - $60 just for an SOC meter. Sad

What do other BMSs do in the real world, as opposed to their descriptions?


This is common. Most inexpensive BMS do what you describe. You need a shunt battery monitor. You can pay a lot and buy a Victron, or buy one of the many Chinese versions that work just fine as well for around the price you already mentioned. I have bought from both Amazon and aliexpress and lean towards Amazon these days as there isn't much price difference. The BMS doesn't count Coulombs and that's what is needed.


Interesting topic on DIYsolar.

https://diysolarforum.com/threads/accuracy-of-overkill-bms-soc.20354/

All the commentators who said that once the battery gets fully charged the BMS counts coulombs is correct - IF there's a significant (>500mA) current. However, if there's no draw for a period of time (say overnight), it reverts to voltage guessing. Then when current is drawn again, it does more fairly accurate sums (but starting from a false premise) until the current drops. Rinse and repeat.

This voltage guessing of course goes wildly off when there's an overall charge.

My BMS's SOC guesses consistently jump between 300Ah and ~160Ah overnight. Half an hours charge of 5A from the solar panel - 300Ah again.

I've juggled the parameters as best I can to match actual SOC voltages and total capacity, and allowed it to cycle a couple of times.

I'll be giving far more credence to the shunt SOC meter when it arrives and gets fitted. Wink
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PostPosted: Thu Jul 22, 2021 3:31 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

Thanks everyone. Systems back to nominal.

Next thought since it appears a few of us are building battery logs.
I'm building a 24V battery with a series connected group of 8 3.4v 280ah batteries.

Anyone looked at any of the DC-DC charge platforms that are vehicle alternator capable?

https://diysolarforum.com/threads/dc-dc-charger-b2b-options-and-general-discussion.17211/

Sterling makes a 12-24.
Kisae DMT makes one with an MPPT.
I believe Victron makes one.
CTEK doesn't support 24V or I'd use it.

Any thoughts?
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PostPosted: Thu Jul 22, 2021 6:21 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

I don't know the other brands, but I know that Victron is highly regarded and Redarc is also very highly regarded. I like my Redarc 40A unit - - it's 12V nominal, I have it set up on the "LiFePo4" setting, and it will also act as my MPPT solar charge controller.

Redarc also sells a single source (ie, without built-in solar charge controller) DC-DC charger in the 24V output class, which will take from 9 volts to 32 volts input and convert that to nominal 24V output:


https://redarcelectronics.com/products/24v-20a-in-vehicle-dc-battery-charger
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PostPosted: Thu Jul 22, 2021 11:16 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

Got my battery pack all done. Fits in the driver box, albeit the studs are too tall... so need to modify the cover. I have the battery foam from GoWesty, so won't short against the metal. Thinking I'll get plastic nut covers for safety. next up... integrating with the van!

Is the hole that held the relay sufficient as a ground? My bms reaches PERFECTLY to that spot.

Rough fitment. The two plywood ends fit snug under the old battery hold down beam, so this will be some form of hold down.
Image may have been reduced in size. Click image to view fullscreen.


Room for BMS to breath. You can see I rough attached the BMS ground to the relay hole. This one location sufficient?
Image may have been reduced in size. Click image to view fullscreen.


The setup as it is in the box. Unfortunately this isn't a "drop in" and requires assembly into the drivers box. The box is clamped with 4 1/8" threaded rod. One end is double nut locked and the other will be nylock.
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BMS attached to the aluminum clamp bars
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PostPosted: Fri Jul 23, 2021 5:34 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

ProspectiveOwnergon wrote:


Is the hole that held the relay sufficient as a ground? My bms reaches PERFECTLY to that spot.


IMO the ground point should be fine as long as you remove any paint to clean metal where the ground will connect.

Is the bolt/screw used there sufficient to securely hold the ground wire in contact with the body?
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Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

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PostPosted: Fri Jul 23, 2021 7:40 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

dobryan wrote:
ProspectiveOwnergon wrote:


Is the hole that held the relay sufficient as a ground? My bms reaches PERFECTLY to that spot.


IMO the ground point should be fine as long as you remove any paint to clean metal where the ground will connect.

Is the bolt/screw used there sufficient to securely hold the ground wire in contact with the body?


It should be able to hold it. It's a tap screw with fine threads.
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PostPosted: Sat Jul 24, 2021 11:17 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

Any thought how to insulate a battery log against stifling heat inside the van?

Heating in cold is easy with a battery mat. Keeping cool around 70f - maybe not so much?
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PostPosted: Sat Jul 24, 2021 11:47 am    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

They're OK between 0°C and 55°C - 32°F and 130°F. If you can leave windows cracked, or a temp-controlled exhaust fan on, you should be fine. I'm assuming you already use a front windshield reflective screen.

Also, even when the main space in the van is hot, the usual places an aux battery will fit will remain cool for ages. Added to which, the battery has a huge thermal inertia.

I suppose you could use a Peltier effect mat (60W ones are ~$7), but then you have to have some heatsink or cooling fan for that.
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PostPosted: Sat Jul 24, 2021 1:05 pm    Post subject: Re: LiFePO4 Batteries: Discussion Thread Reply with quote

As a data point, during the recent heatwave, my LiFePo4 battery pack remained in the 32C to 35C degree temperature range, well below ambient. All the Van windows were open. My BMS has two temp sensors which, hopefully, are fairly accurate.
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