Joff
Posts: 53
Joined: Wed Jan 02, 2019 2:44 am

Parallel HV Battery for added range.

Mon Mar 16, 2020 8:51 am

I've looked into the 60ah to 94 ah battery swap. At this time it seems to be more trouble, cost, and down time than I would like. There are frugal leaf owners that have added a second leaf pack to regain a reasonable range. They wire the second pack in to the cables between the main battery and the "electrical machine." I don't want that much weight added to my 2014 bev I'm looking to build a smaller, lighter, denser, simpler, 96 cell battery that will just give me an extra 20 miles. I figure the guess o meter and state of charge will not be accurate, but I am ok with that. Is the state of charge determined by amp flow? and if so, where is it measuring that? Is it measuring voltage to determine state of charge?

alohart
Posts: 2074
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Parallel HV Battery for added range.

Mon Mar 16, 2020 2:31 pm

Joff wrote:
Mon Mar 16, 2020 8:51 am
I don't want that much weight added to my 2014 bev I'm looking to build a smaller, lighter, denser, simpler, 96 cell battery that will just give me an extra 20 miles.
Fooling the electronics seems daunting. How would regen and battery pack charging work when the main battery pack has 4 times the capacity of the auxiliary battery pack?

Also, the battery pack would need to have a capacity and thus weight about ¼ of that of a 60 Ah battery pack, so a bit more than 100 lb. Seems challenging to install and secure something that large and heavy.
Joff wrote:
Mon Mar 16, 2020 8:51 am
Is the state of charge determined by amp flow? and if so, where is it measuring that? Is it measuring voltage to determine state of charge?
I don't know the answer. However, the voltage jumps up and down with the propulsive and regenerative loads. The damped voltage wouldn't vary much with charge level making voltage quite inaccurate for determining charge level. I'm guessing that coulomb counting and the BMS's calculation of the battery pack capacity are used to calculate the current charge level.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

Joff
Posts: 53
Joined: Wed Jan 02, 2019 2:44 am

Re: Parallel HV Battery for added range.

Mon Mar 16, 2020 3:58 pm

"Fooling the electronics seems daunting. How would regen and battery pack charging work when the main battery pack has 4 times the capacity of the auxiliary battery pack?"

Regardless of the auxiliary battery's capacity, it will follow the voltage of cables attached to the main battery. Although that voltage will fluctuate, it should not go above 396v or below 259v. Like two water towers -one fat, one slender -They have different capacities, but if they are connected, the water levels (in this case voltage levels) will stay the same as they drain or fill.

alohart
Posts: 2074
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Parallel HV Battery for added range.

Mon Mar 16, 2020 4:23 pm

Joff wrote:
Mon Mar 16, 2020 3:58 pm
Regardless of the auxiliary battery's capacity, it will follow the voltage of cables attached to the main battery.
Thanks for reminding me of the basic laws of electricity!
Last edited by alohart on Mon Mar 16, 2020 7:54 pm, edited 1 time in total.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

Joff
Posts: 53
Joined: Wed Jan 02, 2019 2:44 am

Re: Parallel HV Battery for added range.

Mon Mar 16, 2020 4:34 pm

Joff wrote:
Mon Mar 16, 2020 8:51 am
Is the state of charge determined by amp flow? and if so, where is it measuring that? Is it measuring voltage to determine state of charge?
I don't know the answer. However, the voltage jumps up and down with the propulsive and regenerative loads. The damped voltage wouldn't vary much with charge level making voltage quite inaccurate for determining charge level. I'm guessing that coulomb counting and the BMS's calculation of the battery pack capacity are used to calculate the current charge level.
[/quote]
That makes a lot of sense. Voltage doesn't drop a lot in the middle portion of lithium battery's capacity. I hope it would check voltage toward the end of it's range though. It would be sad if it has all this range, and power left in the batteries, but the car just doesn't believe it! It seems leaf owners have managed to get it to work without programming though

Joff
Posts: 53
Joined: Wed Jan 02, 2019 2:44 am

Re: Parallel HV Battery for added range.

Wed Mar 18, 2020 1:40 pm

I decided to make a quick battery out of cells i already have, just to see what happens, if it throws code, triggers turtle mode or somthing. I used 96 8ah packet cells in series, in two banks of 48 cells with a high amp switch in th middle. They are good for 200 amps but I'm using a 50 amp fuse.

Joff
Posts: 53
Joined: Wed Jan 02, 2019 2:44 am

Re: Parallel HV Battery for added range.

Fri Mar 20, 2020 8:39 pm

I built the auxiliary 8ah 360v battery, wired it in with a fuse and a relay to connect and disconnect it. It didn't throw any codes. it showed 65 miles on the guessometer range to start with on a full charge. it traveled 82. I have a 2014 bev showing 13.4 kwh max kappa. There is no indication of extra battery capacity until you get towards the end. The last 2 miles of range seem to go on forever. I kept driving around the neighborhood with one mile of range left I finally gave up with 1 mile range showing and 4% battery left (which seems to indicate a few more miles range) If 96% of the battery got me 82 miles, then 4% should get me closer to 3 miles, I guestamate. I figure this was successful enough to pursue further. I haven't tried posting pictures to a forum before, expect I will be less successful with that! https://photos.google.com/photo/AF1QipM ... 5ab47Kn6yn

alohart
Posts: 2074
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Parallel HV Battery for added range.

Fri Mar 20, 2020 11:40 pm

Joff wrote:
Fri Mar 20, 2020 8:39 pm
I built the auxiliary 8ah 360v battery, wired it in with a fuse and a relay to connect and disconnect it.
Couldn't see your photo because of a page not found error (404).

Sounds like you made great progress! Are you concerned about your auxiliary battery pack cells overheating when the car requires significant power? Do you have a way to balance the charge levels of your auxiliary battery pack cells? I suspect that your photos show how you've mounted your auxiliary battery pack which could become a heavy projectile in a collision.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

Joff
Posts: 53
Joined: Wed Jan 02, 2019 2:44 am

Re: Parallel HV Battery for added range.

Sat Mar 21, 2020 7:39 am

alohart wrote:
Fri Mar 20, 2020 11:40 pm
Joff wrote:
Fri Mar 20, 2020 8:39 pm
I built the auxiliary 8ah 360v battery, wired it in with a fuse and a relay to connect and disconnect it.
Couldn't see your photo because of a page not found error (404).

Sounds like you made great progress! Are you concerned about your auxiliary battery pack cells overheating when the car requires significant power? Do you have a way to balance the charge levels of your auxiliary battery pack cells? I suspect that your photos show how you've mounted your auxiliary battery pack which could become a heavy projectile in a collision.
I was trying to use google photos as host, but only allows me to see it. At least I was correct in assuming I didn't know how to do it, ha ha!
I don't want to pay for photo hosting service, just to show some photos here. It there a free and easy way of posting pictures that anyone could recommend?
I'm using spim08hp cells they can handle 200 amps. I am using a 50 amp fuse. I haven't measured 30 amps flowing when pressing the accelerator. I think the resistance is high enough that it doesn't keep up, so it gets a higher voltage than the main, then equalizes over time. If I connected the aux battery before the main battery is turned on, I get a big spark, high amp momentary surge that can weld my 125amp relay closed. I need to power up the car before connecting the aux battery, then all is well. I have detected no warming of the battery at all.

3pete
Posts: 60
Joined: Tue Mar 19, 2019 9:03 pm

Re: Parallel HV Battery for added range.

Sat Mar 21, 2020 9:16 am

If you're using google photos, you can open the photo in your account and click "share", then "create link". You should get a link that looks something like this:
https://photos.app.goo.gl/t1t3A3uLjKTs7qmz8

We *should* be able to see the picture if you share that URL.

If you want to take a few more steps, you can get a link that works inside the img tags to show up inline in your post:
Go to the link you got in step 1.
Click the picture to open it full screen.
Right click on the new picture an click "copy image location".
Now you should have a link that looks something like:
https://lh3.googleusercontent.com/Ovyvm ... QZjLmLHJA8

If you want maybe a simpler approach, I've heard some people have good success with imgur.com

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