Parallel HV Battery for added range.

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Joff

Well-known member
Joined
Jan 2, 2019
Messages
86
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?
 
Joff said:
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 said:
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.
 
"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.
 
Joff said:
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!
 
Joff said:
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.
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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
 
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.
 
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/AF1QipMvCoQlsC14pGxPxAx5Mal-A_RIGr5ab47Kn6yn
 
Joff said:
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.
 
alohart said:
Joff said:
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.
 
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/OvyvmXpl6knmnATKIgAOPVxMj0kdSYusV0nprTKnwQDqMTmS6H8LGPhvYnWHW1O0k7SJG86SIkTYlLAv0uojGtn2EwPC7ryJqRQdfIx9u1TknOYoqmL4WNgC5sHgYgWqHQZjLmLHJA8

If you want maybe a simpler approach, I've heard some people have good success with imgur.com
 
I forgot to answer all your questions Art. This 8Ah aux battery is just 40 pounds. temporary plywood frame that keeps the cell packets squoze the way they like. I just have it sitting behind the rear seats, it cant go far. No BMS for balancing for now. If I were to cycle this pack a lot, it would be worth adding a bms system, but I will be switching to other batteries if all goes well. Running parallel with the i3's batteries will keep them far from being overcharged or undercharged unless they got way out of balance.
 
Let me know if the link works please! This is the temporary battery that I am already done with https://photos.app.goo.gl/pbChZTe9JR4oZ8xf9
 
I typically can get 10 more miles range than it thinks I can. with a small auxiliary, it's hard to know how much of the range is due to frugal driving and how much is the weather and battery. It took me several days to use it up, doing mainly city driving. In fact, I gave up before running the battery completely out. https://photos.app.goo.gl/2E6hckb9L8gtmBeA7
I will know for sure on the next battery. I bought a full set of 6 battery modules from an i8. The cells within each pack are perfctly balenced but the packs are at different states of charge. I've temporarily wired them in parallel while I charge them with an electric unicycle charger https://photos.app.goo.gl/jt6sujSEgA2exe8V9
 
Joff said:
Let me know if the link works please! This is the temporary battery that I am already done with https://photos.app.goo.gl/pbChZTe9JR4oZ8xf9

Hey! Once you get this sorted I know just the place in your BEV to stash it!

wte-motorbay.jpg
 
Cool stuff! And as a 2014 BEV owner, it'd be pretty neat to be able to take advantage of that empty rex-house in the back for a little more all-electric range!
 
Yes, there is a ton, er, many a cubic foot of unused space! For now I would like to be able to toss it out of the car if it burst into flames, but the longer i play with it the safer it seems. I have not decided if I want to put some of them where the rex would have gone or put them all back further between the motor area an the rear bumper. I could spread them out and keep them all low, or if it is mainly for winter range extention, mayby rear most is the best for winter rear wheel traction. I was concerned that having the modules at different temperatures would cause the voltages to change but they remained the same with a 20f degree difference. I 8 modules I will be using are 27 lbs each so 162 pounds plus what I contain them in. 9kwh all together. Can anyone recommend a source of info on ISTA ? Can it help me tell my car I have more kwh than it previously knew about?
 
I have the I8 modules ready to test, but no where I need to drive, with the covid 19 shelter in place/ quarantine situation. I'm looking into what to do about the bms. i don't want to spend $1200 on a orion system that can handle 96s. As long as I can keep all the cells balanced, I don't need to worry about over voltage or under voltage. I was considering using 6, 60amp 16s bms from aliexpress that are about $30 each i8 module would have it's own. the module would still have to be balanced against each other once in a while. Then I saw somewhere that 16s active battery balancer (not a full battery protection bms) can be wired to another, cascade fashion to cover 32 cells. Maybe I can balance all 96 cell with 6 of them. Can't find info on that. Not even sure what that is called. Here are the balencers I am looking at. https://www.aliexpress.com/item/32967960870.html?spm=a2g0o.cart.0.0.40fc3c00S2ylgT&mp=1
 
I am very interested in your project to get extra range. I to have i3 bev and building a 350vdc 6Ah from lifepo4 cells.
But wondering how you connected your battery pack to the car. Did you splice the HV cable as some cases have done on Leaf.
Or is there an easier way, please help.
 
Martci3 said:
Did you splice the HV cable as some cases have done on Leaf.
Or is there an easier way, please help.

Yes, tapped into HV cables between the battery and the EME. Under the outer layer of insulation, there is stainless steel braiding protecting a inner layer of insulation. Don't let the stainless layer touch the HV cable. It triggers a code that will not allow the HV battery to connect, until the code is cleared. (bimmerlink cleared it) I'm not sure if the stainless layer needs to retain connectivity from one end to the other, but I kept it connected to be on the safe side. I tried a set of 6, 60v bmw i8 battery modules which worked well, but I switched to 6, 2kwh, 60v volvo hybrid battery modules. Higher energy density and they are all from the same unused 2019 pack. I've gotten 104 miles on a charge, I think I can do better, but don't have many reasons to drive far these days. I'm looking into getting more out of the auxiliary pack by using some charger circuitry to move more power out of the aux battery before the main battery says driving fun is over. I figure it will never see as many cycles as the main battery, so I might as well use more of the low voltage "buffer"
 
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