Blue shunt, wrong tool for the job?

[bestconcreteblock]

Trying to use a Victron 300A SmartShunt for a purely resistive discharge capacity test. It is looking like this is not going to give me very useful results...

Setup:

At the start:

Near the end:

At the end after BMS hit low cell voltage before I could hit the contactor switch:

Why does the cumulative Ah drawn not match the last discharge? Also, why does discharged energy not seem right? Even if I use the lowest battery voltage at the end 46V x 60Ah = 2.76 kWh:

Any way to get more data points over this time period on this chart? There were more data points when I first looked at it, but now it is coarse and not very useable over a 27 min discharge?:

Do all my problems stem from the BMS killing the power before I could flip the contactor switch? I am thinking the SmartShunt lost some of its data during the power off time?





DC instant hot water heater:

 

[ricardocello]

Any way to get more data points over this time period on this chart? There where more data points when I first looked at it, but now it is coarse and not very useable over a 27 min discharge?:

It averages the data points after a while to be able to store up to 45 days of data.
The 1 second sample rate is only available as you are watching Trends, but if you keep it running I think you can scroll back to see all the points.
Once you click off of it it retrieves the averaged values.

It isn't an ideal measurement device for this purpose.

Do all my problems stem from the BMS killing the power before I could flip the contactor switch? I am thinking the SmartShunt lost some of its data during the power off time?

Never seen one lose data, but it definitely averages out useful information. So in a sense I guess it is losing information.

 

[ricardocello]

Also, why does discharged energy not seem right? Even if I use the lowest battery voltage at the end 46V x 60Ah = 2.76 kWh:

Because the device is counting coulombs (integrating) to get the Ah and multiplying by the instantaneous voltage to get kWh.
It is much more accurate because it tracks the discharge curve.

 

[bestconcreteblock]

It isn't an ideal measurement device for this purpose.

Thanks for the info. Any suggestions for something that can handle this high C-rate?

 

[ricardocello]

Thanks for the info. Any suggestions for something that can handle this high C-rate?

If your only objective is to determine the Ah capacity of your battery when fully charged, this is very accurate.

If you need to make real-time 1-second sample charts, then it's a pain.

Nice test setup, by the way. Love the blue box and hose.

 

[bestconcreteblock]

Because the device is counting coulombs (integrating) to get the Ah and multiplying by the instantaneous voltage to get kWh.
It is much more accurate because it tracks the discharge curve.

I understand it integrates to get kWh. My point is that even if I use the lowest voltage seen(46V) and multiply it by the measured 60Ah, I get 2.76 kWh. SmartShunt says 2.3kWh?

 

[ricardocello]

Ok, you are expecting the kWh to be between the lowest and highest voltage times the Ah.
Not lower than it. I see your point.

How long are those battery cables, and what size? Some kWh are certainly going into those as heat.
Not saying that’s the reason for the lower number, just asking.

 

[bestconcreteblock]

If your only objective is to determine the Ah capacity of your battery when fully charged, this is very accurate

Thanks, yeah this is my main objective. I am just skeptical that it came out to exactly the battery capacity 60Ah... I guess I shouldn't be.

 

[bestconcreteblock]

How long are those battery cables, and what size? Some kWh are certainly going into those as heat.

1/0 about 5 ft long. SmartShunt is measuring voltage at the end of the battery cables.

 

[bestconcreteblock]

The SmartShunt doesn't just set the "consumed Ah" to the battery capacity set in settings if power is cut by the BMS does it?

 

[bestconcreteblock]

Also, "consumed Ah" won't display on trends during this discharge. Any Ideas why?