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Old 11-21-2018, 12:53 PM   #1
DaveTM
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Default Another Voltage question.....Lithium

Now, I believe that the current setting of my Lithium pack (High Voltage) being set at 57-V is all well and good. I have the BMS set for HV & LV on the correct settings.

I changed my Alltrax AXE4865 controller settings of "Output AMPS" to 75% of what the controller can do, and I set my "Top Speed" to 88% of max.

Now, my question is, the cart is set up for 48-V. Now that I have Lithium installed, the battery pack's voltage is up to 57-V. "Usually" when I think of voltage, I think you just don't go much above what the unit is set up for. Yet, I'm going 9-V above the normal 48-V.

Just wondering the "Hey----hows that work?"
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Old 11-21-2018, 02:01 PM   #2
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Default Re: Another Voltage question.....Lithium

48v is what we consider nominal voltage - voltage of the battery pack when it's charged to 50% of its capacity. When fully charged, it will be above that voltage. When it's towards full depletion, it will be below.

For NMC cells, nominal voltage is 3.7 and max is 4.2. So 14s pack will have nominal of 51.8, max of 58.8.

For Lead-Acid nominal voltage is 2v, max is 2.1v (12.7v for standard battery), so 48v is the nominal for 4 in series (24 cells), 50.8 is max.

So in the end you're only some 6 volts above of what your LA setup would have been, and whether that is permissible for controller... depends on the controller. Pull up the spec sheet for that Altrax, and check what it is.

My "buggy" is also 48v, with 48v Sevcon Gen4. That Sevcon allows for up to 69v of input voltage though, and I run a 60v configuration, with pack charging to 65.8v.
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Old 11-21-2018, 02:34 PM   #3
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Default Re: Another Voltage question.....Lithium

Couldn't find a spec sheet for that particular controller, but Altrax states 60v is max for their 48v models. https://alltraxinc.com/axe-products/
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Old 11-25-2018, 09:52 PM   #4
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Default Re: Another Voltage question.....Lithium

I ran the stock controller on my TXT48 when I switched to lithium. The stock charger cut off at just over 60v (I overcharged the pack accidentally one time) but I would manually cut the charge at some point under 57.6v normally. 58.8v is my pack max (60.3 didn't cause a fire, luckily). The stock controller worked perfectly fine every time I used it. I switched to alltrax before I did the accidental overcharge so the most V the stock controller saw was between 57v and 58v. No issues on the curtis controller. But I didn't run it long term that way either... $0.02

Edit: I am still on the stock solenoid too. FWIW
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Old 11-26-2018, 12:53 AM   #5
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Default Re: Another Voltage question.....Lithium

Quote:
Originally Posted by bronsonj View Post
I ran the stock controller on my TXT48 when I switched to lithium. The stock charger cut off at just over 60v (I overcharged the pack accidentally one time)
That is why you're supposed to have a BMS :) Do you balance your cells manually ?

Quote:
Edit: I am still on the stock solenoid too. FWIW
Yeah, that should be fine.
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Old 11-26-2018, 01:24 PM   #6
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Default Re: Another Voltage question.....Lithium

I balance manually now. I do have a BMS but have not installed it. I purchased a different charger so I no longer have the issue of charging to over 60v.

Actually, I have two of the Chargery BMS modules but I really want to have a quick disconnect method to detach the BMS. I've heard that a BMS failure isn't uncommon (not brand specific, any BMS) and when a BMS module fails the most common failure is to fail in the balancing/discharging state, so it would put a continual load on a single cell until it bricks that cell. This is my first foray into lithium powered vehicles, so I am going off only what I've read.
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Old 11-26-2018, 11:54 PM   #7
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Default Re: Another Voltage question.....Lithium

Quote:
Originally Posted by bronsonj View Post
I balance manually now. I do have a BMS but have not installed it. I purchased a different charger so I no longer have the issue of charging to over 60v.

Actually, I have two of the Chargery BMS modules but I really want to have a quick disconnect method to detach the BMS. I've heard that a BMS failure isn't uncommon (not brand specific, any BMS) and when a BMS module fails the most common failure is to fail in the balancing/discharging state, so it would put a continual load on a single cell until it bricks that cell. This is my first foray into lithium powered vehicles, so I am going off only what I've read.
Biggest concern is not around overcharging the entire pack, but around cells getting out of balance and being pushed beyond operational limits. Depending on how well your cells are matched, that may be a minor or a major concern, which a good BMS would address.

BMS failures are common for BMSes coming from aliexpress :) If you go with a serious vendor, it's not really a concern. Note that shunt balancing (resistor) is typically the approach in cheaper BMS systems. Serious automotive BMSes do active balancing, where energy in a cell with higher voltage is dumped into a cell with lower voltage, so bricking a cell like you're describing isn't possible by design.

I started having an issue with my Chargery charger which is only 1 month old, it keeps going to "connect break" state even though there is a proper connection to individual battery. After reading that other report about their charger, I wouldn't trust them with managing my pack.
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Old 11-27-2018, 05:07 PM   #8
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Default Re: Another Voltage question.....Lithium

Please forgive/correct anything that is way out in left field. This is my first lithium powered project for anything bigger than my cordless tools...

I get what you're saying. I looked for BMS systems that transferred energy and the cheapest one I found was over $800 (before all the add-ons) for a BMS that would handle 14 cells. Seems 14S is an odd size, I found many 12S and 16S in many places but 14S was different. I'm new to the BMS world so if the BMS didn't state they could handle fewer cells I have to assume it can't, I know some can handle fewer cells but I don't know if that's standard practice among all BMS modules.

FWIW, I bought the 58.8v lithium and 16.8v lithium aux battery for around $700 total (I can look up actual amount, but close enough for now). I figure spending more on the BMS than I spent on the battery didn't make much sense. I also wanted a BMS I could set the max Vpc to be lower than 4.2v and most like to fully charge the battery and don't actually balance the individual cells until very close to full charge. So I'd see a BMS that would charge to 4.2vpc and not start the balancing until 4.18vpc. I didn't like that because I want to terminate the charge at 4.1vpc.

Since the max is 58.8 and the cells are all within 0.01v of each other I set my mental cutoff to 57.6v (4.1vpc) and in practice I normally cut the voltage at 56.6v with the new charger. If I took the cells to 3v each, that'd be 42v pack. I set my controller to cutoff at 45.5v. This gives me a pretty good margin of safety on the charge and discharge.

I routinely check the cell variation and they all are staying within 0.01v thus far.

So I do agree with you that a more expensive BMS would solve these issues. I haven't seen one that I consider to be a reasonable price yet so I give myself a buffer at the charge and discharge cutoffs.
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Old 11-27-2018, 05:12 PM   #9
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Default Re: Another Voltage question.....Lithium

Although, if you know of a BMS that you think may work for me and doesn't cost more than my batteries I'm game to check it out. I've proven I am fully capable of regular mistakes, so I am not against a decent BMS at a reasonable price.
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Old 11-27-2018, 05:27 PM   #10
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Default Re: Another Voltage question.....Lithium

The Zeva BMS will allow you to configure the individual cell voltages for lower, upper and balancing as you mentioned.

At the very least you should consider using one of these programmable voltmeters that can automatically control the charge voltage, the pack low voltage and pack high voltage (Regen) disconnect using external relays.

While it cannot provide single cell protection is much better than manually handling disconnects.

https://www.lightobject.com/Programm...stem-P408.aspx

https://www.lightobject.com/Programm...stem-P407.aspx
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