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jimf909 Samba Member
Joined: April 03, 2014 Posts: 7462 Location: WA/ID
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Posted: Wed Jul 14, 2021 9:44 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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This was a superb read. Thank you. I need to leave the vanagon cul de sac more often.
_________________ - Jim
Abscate wrote: |
Do not get killed, do not kill others.
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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.
Past: 1985 Westy Camper - 1.9 wbx, 2wd, manual trans, Merian Brown, (sold after 17 years to Northwesty who converted it to a Syncro). |
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dobryan Samba Member
Joined: March 24, 2006 Posts: 16501 Location: Brookeville, MD
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gtinseth Samba Member
Joined: July 25, 2019 Posts: 76 Location: NW California
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Posted: Thu Jul 15, 2021 10:37 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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 Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Fri Jul 16, 2021 3:37 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. 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.
What do other BMSs do in the real world, as opposed to their descriptions? _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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ProspectiveOwnergon Samba Member
Joined: May 22, 2020 Posts: 211 Location: SoCal
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Posted: Tue Jul 20, 2021 7:21 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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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gtinseth Samba Member
Joined: July 25, 2019 Posts: 76 Location: NW California
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Posted: Tue Jul 20, 2021 11:45 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. 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.
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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fxr Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Wed Jul 21, 2021 8:38 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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Thanks for the confirmation. I ordered a cheapo coulomb counter yesterday.
$20 inc postage from China. Huge long link:
https://www.banggood.com/PZEM-015-Battery-Tester-D...02448.html _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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rmcd Samba Member
Joined: October 29, 2010 Posts: 1348 Location: PNW - its a dry rain.
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Posted: Wed Jul 21, 2021 9:57 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. _________________ VW LT40 build. Like a Vanagon but 30% larger in every direction and 40% slower even in metric.
https://www.thesamba.com/vw/forum/viewtopic.php?t=749359&highlight= |
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gtinseth Samba Member
Joined: July 25, 2019 Posts: 76 Location: NW California
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Posted: Wed Jul 21, 2021 11:17 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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rmcd wrote: |
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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fxr Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Thu Jul 22, 2021 9:16 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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rmcd wrote: |
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. _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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dobryan Samba Member
Joined: March 24, 2006 Posts: 16501 Location: Brookeville, MD
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Posted: Thu Jul 22, 2021 9:32 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. 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.
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/ _________________ Dave O
'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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fxr Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Thu Jul 22, 2021 12:16 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. 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.
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. _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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rmcd Samba Member
Joined: October 29, 2010 Posts: 1348 Location: PNW - its a dry rain.
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Posted: Thu Jul 22, 2021 3:31 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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? _________________ VW LT40 build. Like a Vanagon but 30% larger in every direction and 40% slower even in metric.
https://www.thesamba.com/vw/forum/viewtopic.php?t=749359&highlight= |
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Howesight Samba Member
Joined: July 02, 2008 Posts: 3274 Location: Vancouver, B.C.
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Posted: Thu Jul 22, 2021 6:21 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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 _________________ '86 Syncro Westy SVX |
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ProspectiveOwnergon Samba Member
Joined: May 22, 2020 Posts: 211 Location: SoCal
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Posted: Thu Jul 22, 2021 11:16 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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.
Room for BMS to breath. You can see I rough attached the BMS ground to the relay hole. This one location sufficient?
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.
BMS attached to the aluminum clamp bars
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dobryan Samba Member
Joined: March 24, 2006 Posts: 16501 Location: Brookeville, MD
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Posted: Fri Jul 23, 2021 5:34 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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? _________________ Dave O
'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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ProspectiveOwnergon Samba Member
Joined: May 22, 2020 Posts: 211 Location: SoCal
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Posted: Fri Jul 23, 2021 7:40 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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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rmcd Samba Member
Joined: October 29, 2010 Posts: 1348 Location: PNW - its a dry rain.
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Posted: Sat Jul 24, 2021 11:17 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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? _________________ VW LT40 build. Like a Vanagon but 30% larger in every direction and 40% slower even in metric.
https://www.thesamba.com/vw/forum/viewtopic.php?t=749359&highlight= |
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fxr Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Sat Jul 24, 2021 11:47 am Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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Howesight Samba Member
Joined: July 02, 2008 Posts: 3274 Location: Vancouver, B.C.
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Posted: Sat Jul 24, 2021 1:05 pm Post subject: Re: LiFePO4 Batteries: Discussion Thread |
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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. _________________ '86 Syncro Westy SVX |
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