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

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
Ok I missed that video. Sorry. But still....
I obviously missed where ever it is you said you owned this one. Duh me
Secondly. Bus does admit he does not know all there is to know about the juntek so he may have slipped up on a feature or two himself.

But still....
He did a good job of it and is the only video that went into depth etc. :)
 

snoobler

Solar Honey Badger
I didn't read the whole thread. Please forgive me if I've repeated something.

I own one as well. Used it for about a year before I installed the Victron BMV. It measures both ways and "net," i.e., if you were to have a load and a charge at the same time, it reports the net of the two, e.g., 10A load and a 20A charge would should as a 10A charge.

Do not connect backwards.

IMHO, you should program it for 140Ah and set it SoC to 50%. It should then count input current and hit 100% when you have input 70Ah. If you leave it connected during use, it will count current out and indicate 0% when you've used the 140Ah programmed.

My only real objection (what can you expect from a $50 BM?) is the unclear charge termination criteria, i.e., what resets it to 100%? If it's in the video, I didn't watch it, and I never figured it out from the instructions. I would just periodically set it to 100% when my batteries were fully charged and in float mode. Based on a comparison to batteries at or near a resting state, it was close enough for me.
 

Bob B

Photon Sorcerer
The purpose of reversing the wires on the shunt .... at least the connotations I remember .... is for calibration purposes and testing under controlled amperage. If you have an adjustable power supply you can test / calibrate current flow for both charge and load by reversing the leads.

I did this to calibrate the shunt on my BMS. Even though you are sending a constant charge current, you trick the BMS into thinking it is load current.

This was not derived from watching the posted video.
 

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
I didn't read the whole thread. Please forgive me if I've repeated something.

I own one as well. Used it for about a year before I installed the Victron BMV. It measures both ways and "net," i.e., if you were to have a load and a charge at the same time, it reports the net of the two, e.g., 10A load and a 20A charge would should as a 10A charge.

Do not connect backwards.

IMHO, you should program it for 140Ah and set it SoC to 50%. It should then count input current and hit 100% when you have input 70Ah. If you leave it connected during use, it will count current out and indicate 0% when you've used the 140Ah programmed.

My only real objection (what can you expect from a $50 BM?) is the unclear charge termination criteria, i.e., what resets it to 100%? If it's in the video, I didn't watch it, and I never figured it out from the instructions. I would just periodically set it to 100% when my batteries were fully charged and in float mode. Based on a comparison to batteries at or near a resting state, it was close enough for me.
Thank you. :)
 

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
The purpose of reversing the wires on the shunt .... at least the connotations I remember .... is for calibration purposes and testing under controlled amperage. If you have an adjustable power supply you can test / calibrate current flow for both charge and load by reversing the leads.

I did this to calibrate the shunt on my BMS. Even though you are sending a constant charge current, you trick the BMS into thinking it is load current.

This was not derived from watching the posted video.
Yes I seen a video doing that as well.
My best guess is that I seen older videos and that they have updated the coulomb meters now.
Thanks Bob. :)
 

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
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.
Found it.
My apologies and thank you again for your help. :)
 

JoeHam

Photon Sorcerer
To use a unidirectional shunt as bidirectional couldn’t one just use a DPDT switch to reverse the shunt leads?

That would remove the overhead of relays.
 

Bob B

Photon Sorcerer
To use a unidirectional shunt as bidirectional couldn’t one just use a DPDT switch to reverse the shunt leads?

That would remove the overhead of relays.
Can you post an example of a unidirectional shunt? What would you be trying to achieve by doing this?
 

JoeHam

Photon Sorcerer
Maybe my terminology is off but I’m thinking of one of the cheap Drok monitors that only measures one way current flow.

In that case you could measure one way during charge then reverse the shunt wires physically or via a DPDT switch during discharge. This is my idea but I admit I’ve never tried it.
 

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
Maybe my terminology is off but I’m thinking of one of the cheap Drok monitors that only measures one way current flow.

In that case you could measure one way during charge then reverse the shunt wires physically or via a DPDT switch during discharge. This is my idea but I admit I’ve never tried it.
I just went through this whole thing in a post I made recently.
I got a juntek and it measure two way amperage's.
https://diysolarforum.com/threads/so-reversing-a-shunt-is-almost-as-good-as-a-bms.14134/
 

Bob B

Photon Sorcerer
I'm not familiar with the one way monitors you are talking about, but I don't think you would be very happy with a setup like that.
There are inexpensive shunt type monitors that monitor both charge and load.

Will has a link to one on this page.

 
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Zil

Solar Addict
Now that we know the battery monitor with shunt can read voltage of the whole battery and indicate the SOC if it is properly calibrated, we still need a BMS on a lithium battery. Each cell needs to be monitored while charging and while discharging. It is very common for one cell in the battery to become over-voltage or under-voltage and that can wreck the battery.
 
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SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
Now that we know the battery monitor with shunt can read voltage of the whole battery and indicate the SOC if it is properly calibrated, we still need a BMS on a lithium battery. Each cell needs to be monitored while charging and while discharging. It is very common for one cell in the battery to become over-voltage or under-voltage and that can wreck the battery.
Yes, true.
But what if you do not have a BMS? hmmmm.
The plot thickens. Oh look, someone said as much earlier lol.
 

Zil

Solar Addict
If you do not have a BMS on a lithium battery, you risk ruining your battery. It is that simple. hmmmm
 

Hedges

I See Electromagnetic Fields!
I don't have a BMS on my lithium battery. It's in my iPhone. It just has a battery charger. (and low-voltage shutdown, of course)
 

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
I don't have a BMS on my lithium battery. It's in my iPhone. It just has a battery charger. (and low-voltage shutdown, of course)
And I just used my ocd and all cells came out 3.35 volts :)
Pretty happy with that. Oh yeah, it was also after paralleling them for 2 hours and 48 minutes as well. LOL.
 

snoobler

Solar Honey Badger
And I just used my ocd and all cells came out 3.35 volts :)
Pretty happy with that. Oh yeah, it was also after paralleling them for 2 hours and 48 minutes as well. LOL.

They will drift. Paralleling cells without current flow transfers almost no charge. Current flows when there's a voltage difference. When you parallel them, their voltages almost instantly equalize. There is an initial surge and then it drops to low milli or micro amps. If you do this for weeks, it can be meaningful, but doing it for 2.75 hr is just a placebo.

Once you series them and subject them to a charge/discharge, they will diverge again.
 

Hedges

I See Electromagnetic Fields!
She's charging them in parallel, due to lack of BMS.
Then discharging them in series while scooting across town.
I think that completely solves all the technical problems.
 

Gazoo

Dumb Dumb
And I just used my ocd and all cells came out 3.35 volts :)
Pretty happy with that. Oh yeah, it was also after paralleling them for 2 hours and 48 minutes as well. LOL.
Have you thought about possibly posting some photos of your build and how you carry it on your scooter? I think it's fascinating what you have accomplished and the care you have put forth to protect your cells without a BMS.
 
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