So reversing a shunt is almost as good as a BMS?

SherylinRM

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I only get one shot at things as I am very poor sooooo.
If you reverse a shunt like the juntek one I have. Instead of measuring amps out it will measure amps in. In this correct or no?

Secondly. If it does measure amps in. Would this not be a much better way to measure SOC [state of charge] than measuring voltage [which is very inaccurate]?

Cause I was just thinking that this would be helpful to me when recharging until i get a proper BMS etc.

Ideas?
Anyone even tried this yet?

Thanks :)
 

gnubie

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Yes, measuring amp hours in / out is a much better way of tracking SOC, especially with lifepo4's mostly flat discharge curve. This is what decent battery meters do. If the Juntek only measures current in one direction, yes, flipping it will let it read current going the other way.
 

Dzl

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I only get one shot at things as I am very poor sooooo.
If you reverse a shunt like the juntek one I have. Instead of measuring amps out it will measure amps in. In this correct or no?

Secondly. If it does measure amps in. Would this not be a much better way to measure SOC [state of charge] than measuring voltage [which is very inaccurate]?

Cause I was just thinking that this would be helpful to me when recharging until i get a proper BMS etc.

Ideas?
Anyone even tried this yet?

Thanks :)

You are correct that a Shunt can more correctly measure state of charge (if it can accurately measure current, meaning all current in and out of the battery must pass through it).

But I think there are a couple of misconceptions in your broader question, to clarify a few general points:
  1. A shunt--at least those I am familiar with-- is bi-directional, it will measure the net current in either direction, but it has to measure all current in both directions to accurately report state of charge. This is why most people locate it very close to the battery so it captures all current in and out of the battery.
  2. A shunt is not a replacement for or alternative to a BMS, they serve very different purposes (with some overlap). A shunt is a measurement device, it is not designed to control or protect anything else (though some could be used to do so to a degree). A BMS on the other hand is designed to protect and manage your battery, SOC estimation/monitoring is an optional secondary feature that many have, but not the main purpose.

With a somewhat more sophisticated battery monitor I believe you could come up with some sort of SOC based disconnect system using a relay or something. But it would not have the same functionality as a BMS, and it would not be aware of any cell level conditions.
 

Dzl

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If you have (or could source) a battery monitor that can control a relay, you could probably use SOC to trigger charge and/or discharge disconnection. I think the Victron BMV is capable of this but its not cheap (more expensive than a decent BMS).

Alternatively if you actively monitor the pack yourself while charging you could be the relay :) and just watch the monitor relatively closely
 

SherylinRM

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You are correct that a Shunt can more correctly measure state of charge (if it can accurately measure current, meaning all current in and out of the battery must pass through it).

But I think there are a couple of misconceptions in your broader question, to clarify a few general points:
  1. A shunt--at least those I am familiar with-- is bi-directional, it will measure the net current in either direction, but it has to measure all current in both directions to accurately report state of charge. This is why most people locate it very close to the battery so it captures all current in and out of the battery.
  2. A shunt is not a replacement for or alternative to a BMS, they serve very different purposes (with some overlap). A shunt is a measurement device, it is not designed to control or protect anything else (though some could be used to do so to a degree). A BMS on the other hand is designed to protect and manage your battery, SOC estimation/monitoring is an optional secondary feature that many have, but not the main purpose.

With a somewhat more sophisticated battery monitor I believe you could come up with some sort of SOC based disconnect system using a relay or something. But it would not have the same functionality as a BMS, and it would not be aware of any cell level conditions.
Yes, I am aware they are different. However my point this time was to measure SOC, not to protect etc.
I am not aware that the Juntek can do two way though.
Thanks for your input. :)
 

SherylinRM

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Yes, measuring amp hours in / out is a much better way of tracking SOC, especially with lifepo4's mostly flat discharge curve. This is what decent battery meters do. If the Juntek only measures current in one direction, yes, flipping it will let it read current going the other way.
Thank you :)
 

SherylinRM

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If you have (or could source) a battery monitor that can control a relay, you could probably use SOC to trigger charge and/or discharge disconnection. I think the Victron BMV is capable of this but its not cheap (more expensive than a decent BMS).

Alternatively if you actively monitor the pack yourself while charging you could be the relay :) and just watch the monitor relatively closely
It is literally sitting beside me as I type LOL.
So I am the BMS at this point, AND the monitor, AND the relay AND...... LOL :)
 

Dzl

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Dzl

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Yes, I am aware they are different. However my point this time was to measure SOC, not to protect etc.
Okay Just wanted to make sure, I got thrown off by the title of the thread
 

gnubie

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Hey guys, I found a new BMS on aliexpress. It uses a new AI method of monitoring the battery. The process is:

- Check battery and cell voltage at start of charging and estimate time to first SOC check
- wait that interval paying no attention to the battery at all during this stage of charging
- once interval has elapsed start checking cells and battery voltage every 15 minutes + / - 5 minutes but randomly missing one or two checks in a row
- once any single cell is detected over voltage completely halt charging
- make no attempt to balance cells as no one really wants that anyway

It's listed under the SRM brand

;)
 

SherylinRM

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Do you have a link to the Juntek? Or a model number?

Does this look like what you have?
Yes, that is it exactly. I have the 1300 version.
 

Dzl

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Yes, that is it exactly. I have the 1300 version.

In that case, this is stated in the description:
The measuring module can detect the current in both directions. It is not necessary to change the wiring mode during the charge and discharge of the battery

And I found this video (only watched the first 5 minutes but seems like there is a good bit of info in there):
 

SherylinRM

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Hey guys, I found a new BMS on aliexpress. It uses a new AI method of monitoring the battery. The process is:

- Check battery and cell voltage at start of charging and estimate time to first SOC check
- wait that interval paying no attention to the battery at all during this stage of charging
- once interval has elapsed start checking cells and battery voltage every 15 minutes + / - 5 minutes but randomly missing one or two checks in a row
- once any single cell is detected over voltage completely halt charging
- make no attempt to balance cells as no one really wants that anyway

It's listed under the SRM brand

;)
LOL I wish.
I thought everyone knew by now.
I ordered the full works from Chargery. Paid for it and everything etc.
But for whatever reason Citibank decided to screw me around and I lost money for the privilege as well. So now I have to save my money and try again. 😢🥺😭
Anyhow, until then I have no choice but to use the batteries I have so I am trying to find work arounds and to do it safely until I can finally get what I need [a lifepo charger and proper BMS].
I am looking at maybe affording it next January [I hope].

BUT, until then I have to use my mobility scooter nearly every day and so it needs to be safely charged etc.

I know there are experimenters here and so I ask what looks like weird questions..
Bottom line is I have no charger or BMS and yet need to charge and use my batteries.

Soooooo. :) 🤪 :sneaky::rolleyes::oops:o_O:)
 

SherylinRM

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In that case, this is stated in the description:


And I found this video (only watched the first 5 minutes but seems like there is a good bit of info in there):
Thanks. Bus and myself have talked rather a bit about it which is why I bought it. :)
It is a good video. :)
 

Dzl

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Thanks. Bus and myself have talked rather a bit about it which is why I bought it. :)
It is a good video. :)

Sweet, not much I can share than that you haven't already heard.

At about 3:18 he mentions it measures current in both directions, and a bit before that he mentions in passing how it could potentially be used to switch a relay, though doesn't get into specifics.
 

SherylinRM

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Sweet, not much I can share than that you haven't already heard.

At about 3:18 he mentions it measures current in both directions, and a bit before that he mentions in passing how it could potentially be used to switch a relay, though doesn't get into specifics.
LOL yes, he mentions the relay a few times tongue in cheek later LOL. :)
 

Gazoo

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I have the 1100 and have been using it over a year and I love it. Yes it measures current in both directions. But it also can be used with a relay. OCP, LVD, OVD can all be set to control a relay. I tested the basic on/off feature of it to control a relay and it worked perfectly. It does have some design flaws, but nothing that would effect performance. For coulomb counting I have found it to be accurate. I really like that it's wireless and can be powered and used in several configurations. I am planning to eventually get the 1300 for my battery build.
 

SherylinRM

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I have the 1100 and have been using it over a year and I love it. Yes it measures current in both directions. But it also can be used with a relay. OCP, LVD, OVD can all be set to control a relay. I tested the basic on/off feature of it to control a relay and it worked perfectly. It does have some design flaws, but nothing that would effect performance. For coulomb counting I have found it to be accurate. I really like that it's wireless and can be powered and used in several configurations. I am planning to eventually get the 1300 for my battery build.
So literally all you do is reverse it on the negative output. Correct?
 
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