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Old 01-24-2020, 07:33 AM   #21
fstop
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

Quote:
Originally Posted by NoleFan4Ever View Post
Here is mine https://www.ebay.com/itm/28369594043...m=283695940436 it is a 58.8v 15A with dual cooling fans and adjustable Pot so you can trim to your preferred voltage. We have used 8 of these and they are great.

Specify the AC and DC type plug in the Notes at checkout and it will be ready right out the box. Mine was pushing right at 59 volts so I trimmed it back to 58.2 volts. You will see in the pictures where the trim pot is.
How far can you trim the voltage back? Can you take it down as low as 54.xx?

Considering it for a take-along charger for LifePo4 16s. Not sure this would be ideal in this case as I'm not sure you'd get a perfect 100%SOC because I think the constant voltage part of the charge might be the same, but perhaps the tapering current part at the end may be different between Leaf chemistry and LifePo4?

In my use case for this unit I would be less interested in a 100% SOC as long as it would do 90+, and mainly, that it would do it safely / gently on the battery.

Most of the Amazon chargers are 10a (and I wonder if they are even that, judging by the looks of some of them) so I like that this one is 15a and seems to look the part.

Thanks!
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Old 01-24-2020, 07:34 AM   #22
Sergio
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

The lithium battery only delivers about half of its capacity at 0C and the increased internal resistance at those temperatures really limits the current discharge.

As I had mentioned there has been some unusual cold weather for this region recently, 20's F at night and low 30's F during the day.

I came home one night and a neighbor asked me to help him get this internet/router back online.

I got in the cart and the battery temperature was 36F, normally while going up the hill from my house the cart uses 180 amps for about 100 yards, that night the current was only 120 amps since the Alltrax controller started to limit the current based on the pack voltage dropping to near the 46v low voltage setting.

I have a couple of small ptc (50C curie temp) heating elements that I purchased last year and I tested the other night by just taping them to the outside of the metal box.

The box was 40F when I turned them ON, the temp near the ptc got to 90F eventually, but due to the large thermal mass that needed to warm up the temperature quickly dropped as you moved away from the ptc.

I think I may follow my original plan this weekend which was to use some leftover aluminum flashing to make an envelope with the two ptc inside.

I also have some 40C disc style NC temp limit switches that I will attach to the assembly.

The idea is to place the hot plate assembly inside my metal box over the batteries where the heat will be trapped by the enclosed box and hopefully warm the cell pouches quickly.

I powered the ptc with pack voltage and the current was under 1 amp.

I will post an update once I installed it and have a chance to test it.

That charger I linked was under $100 and it does a nice job lowering the current during the end of the absorption charge (to less than 1 amp) which improves the effectiveness of the balancing circuit when active.

The charger NoleFan4Ever posted looks good too but I would recommend lowering the charger output to 56.7V or 4.05vpc.

The batteries will provide twice the life when charged to 4.05vpc as they would if charged to 4.15vpc and it is also beneficial if you use regenerative brake since allows some headroom to absorb the regen current.
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Old 01-24-2020, 07:42 AM   #23
fstop
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

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Originally Posted by Sergio View Post
The lithium battery only delivers about half of its capacity at 0C and the increased internal resistance at those temperatures really limits the current discharge.

As I had mentioned there has been some unusual cold weather for this region recently, 20's F at night and low 30's F during the day.

I came home one night and a neighbor asked me to help him get this internet/router back online.

I got in the cart and the battery temperature was 36F, normally while going up the hill from my house the cart uses 180 amps for about 100 yards, that night the current was only 120 amps since the Alltrax controller started to limit the current based on the pack voltage dropping to near the 46v low voltage setting.

I have a couple of small ptc (50C curie temp) heating elements that I purchased last year and I tested the other night by just taping them to the outside of the metal box.

The box was 40F when I turned them ON, the temp near the ptc got to 90F eventually, but due to the large thermal mass that needed to warm up the temperature quickly dropped as you moved away from the ptc.

I think I may follow my original plan this weekend which was to use some leftover aluminum flashing to make an envelope with the two ptc inside.

I also have some 40C disc style NC temp limit switches that I will attach to the assembly.

The idea is to place the hot plate assembly inside my metal box over the batteries where the heat will be trapped by the enclosed box and hopefully warm the cell pouches quickly.

I powered the ptc with pack voltage and the current was under 1 amp.

I will post an update once I installed it and have a chance to test it.

That charger I linked was under $100 and it does a nice job lowering the current during the end of the absorption charge (to less than 1 amp) which improves the effectiveness of the balancing circuit when active.

The charger NoleFan4Ever posted looks good too but I would recommend lowering the charger output to 56.7V or 4.05vpc.

The batteries will provide twice the life when charged to 4.05vpc as they would if charged to 4.15vpc and it is also beneficial if you use regenerative brake since allows some headroom to absorb the regen current.
Thanks for the details and your experience with the temps - similar to what I noted in terms of performance change (and probably range).

I do keep my cart in a garage, which usually doesn't get nearly as cold / hot as outside, but we've had same cold weather as you but not quite as cold here.

In this case I wonder if the cells "self heat" as you begin to discharge them
?
In other words, as long as the cell temperatures at the beginning of your ride are acceptable, even though the outside ambient temps may be 35 or 40, would the cells keep themselves warm (as long as you are using them some)?

Can you adjust charge voltage on the charger you linked?
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Old 01-24-2020, 07:53 AM   #24
Sergio
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

The cells would warm up during use but it could create localized heat due to the elevated internal resistance, of course you could just take it easy when the pack is near 32F, but I enjoy playing around with this stuff.

That charger has a multi-turn trim-pot to adjust the output voltage which makes it very easy and granular to adjust and the no load voltage adjustment is exactly the same as under load.

The first two pictures on the first post shows the first charge with 9.91 amps and the location of the adjustment trim pot for that particular charger.
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Old 01-24-2020, 08:11 AM   #25
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

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Originally Posted by Sergio View Post
The cells would warm up during use but it could create localized heat due to the elevated internal resistance, of course you could just take it easy when the pack is near 32F, but I enjoy playing around with this stuff.

That charger has a multi-turn trim-pot to adjust the output voltage which makes it very easy and granular to adjust and the no load voltage adjustment is exactly the same as under load.

The first two pictures on the first post shows the first charge with 9.91 amps and the location of the adjustment trim pot for that particular charger.
Thanks for the info. Yes - even yesterday (52 degrees maybe) I was taking it a little easy on the cart, as I could tell it wasn't what it was when it was 80f a week or so ago.

Noted that the cell specs for my LifePo4 say if temp is less than 50f, max. charge v should be a little less (3.6v / cell -vs- 3.65) than if it is warmer, and also charge current should be .2c max at these lower temps. I would have thought all that would be relevant at closer to freezing - not up as high as 50f.

Would that charger you have (if max v. adjusted down a bit) work for LifePo4?
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Old 01-24-2020, 09:41 AM   #26
Volt_Ampere
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

I have a meter to measure internal resistance of my smaller Lipo batteries and they do change about a factor of 2 for 10 deg C change in temp. I used to fly electric planes in 40 degree temps before moving to Arizona and I used to warm my batteries before flying to get the performance back. Yes - they do self heat but not quick enough to get their performance back. I have 14 leaf modules so my IR is half what it would be with 7 modules and I don't notice much performance change at 50 degrees vs 80 here. I don't go out in my cart if it's below 50 degrees anyway and I store it in my garage so it probably never goes below 60 over night.
Electric cars do have battery temperature control (at least most do) to keep them from overheating and overcooling. Nissan Leaf did not have good battery thermal management and they were a complete failure in Phoenix. The batteries got too hot in summer and failed. Our carts don't tax the batteries as much but life will suffer in hot climates relative to cooler ones.
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Old 01-24-2020, 09:58 AM   #27
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

I agree, my comment about "localized heat due to the elevated internal resistance" when cold is also the reason they recommend lower charging current when really cold.

I think when running an FET based BMS in hot weather the biggest concern is the BMS itself heating up due to high current.

As far as the charger look for a lithium ion charger and not a LiPo charger, like the one below (I don't know anything about this charger, just did I quick search):
https://www.amazon.com/dp/B07CXQBQ8D..._t2_B07Q125N9C
I really didn't have any plans to drive the cart when it was that cold, but since I did and experienced the poor performance, I decided to play around with pre-heating batteries.

Even if it turns out not to be feasible, it is a good weekend project.
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Old 01-24-2020, 10:11 AM   #28
Volt_Ampere
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

I think to successfully heat the batteries you need a low level heat and some insulation. You can't heat them quickly and evenly with an external heater. I would only resort to doing this if I were using my cart in winter weather - which I am not. I like to drive in a nice warm car when it's cold out rather than in an open cart. By the way, FLA batteries suffer the same behavior when cold. They lose capacity and current capability when cold.
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Old 01-24-2020, 01:25 PM   #29
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

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Originally Posted by fstop View Post
How far can you trim the voltage back? Can you take it down as low as 54.xx?
-snip-
I am not 100% sure, but I believe they will. The reason I say that is when I was setting mine, I made an adjustment and did not realize I had hit the "Hold" button and when I released it, the meter changed to 56.45 volts. There was still more adjustment left on the pot.
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Old 01-24-2020, 02:59 PM   #30
fstop
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Default Re: Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

Quote:
Originally Posted by NoleFan4Ever View Post
I am not 100% sure, but I believe they will. The reason I say that is when I was setting mine, I made an adjustment and did not realize I had hit the "Hold" button and when I released it, the meter changed to 56.45 volts. There was still more adjustment left on the pot.
Thank you!
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