Accuracy of BMS temperature cutout

[rusty69]

Anyone measured it? 

 

Particularly the JBD flavour. 

 

My victron battery sense is showing 2 degrees C. 

 

My BMS is showing 7 degrees C. Both are in a similar position. 

 

Quite a difference. 

 

I haven't got two other thermometers or a calibrated one to check them. 

[magnetman]

Is the battery itself creating heat ?

Oops they are in the same place. 

 

Ignore. 

 

Bit chilly this morning. 

[rusty69]

1 minute ago, magnetman said:

Is the battery itself creating heat ?

Oops they are in the same place. 

 

Ignore. 

 

Bit chilly this morning. 

Yeah. Both stuck to the side of the case. I better check now I've said that though. Maybe one has moved. 

 

 

[magnetman]

An infrared thermometer is a good toy. 

 

You could point it at one sensor then the other and see if they are the same temperature. 

[rusty69]

Just now, magnetman said:

An infrared thermometer is a good toy. 

 

You could point it at one sensor then the other and see if they are the same temperature. 

Good point. I have one of those somewhere. 

 

Any idea where I put it? 

[magnetman]

diysolarforum.com/threads/jbd-temp-sensor-out-of-wack.45278/

 

You are not alone.

 

 

Yes it is in the box under the step. 

[Guest]

Are these things not of debatable value anyway?

 

If they only sense one battery what about the rest of the bank?

 

Ours sensed an overheating battery and shut the charger down. But it just happened to be on the one which was overheating. If it hadn't been the charger would have carried on.

[rusty69]

10 minutes ago, M_JG said:

Are these things not of debatable value anyway?

 

If they only sense one battery what about the rest of the bank?

 

Ours sensed an overheating battery and shut the charger down. But it just happened to be on the one which was overheating. If it hadn't been the charger would have carried on.

Yes, I suppose they are. And probably worthless if not accurate. 

 

If it turns out my victron is the accurate one, then the BMS is not going to cut off at 0 degrees. 

 

I suppose I could change the cut out values to compensate, but not ideal. 

 

The other option is to get a better BMS with more than one temp sensor and measure each bank/cell

[magnetman]

In the thread I found on the solar forum someone said you can calibrate the sensor on the BMS. 

[rusty69]

Just now, magnetman said:

In the thread I found on the solar forum someone said you can calibrate the sensor on the BMS. 

I'll have a go at this later 

When I find my IRT. 

 

Any idea where it is? 

[magnetman]

44 minutes ago, magnetman said:

diysolarforum.com/threads/jbd-temp-sensor-out-of-wack.45278/

 

You are not alone.

 

 

Yes it is in the box under the step. 

I already told you. 

[rusty69]

It wasn't there. Maybe the rat ate it. 

Edited November 30, 2023 by rusty69

[magnetman]

Maybe the rat has been fiddling with your BMS..

Rodents which find themselves in cold boats have been known to attempt to cause battery fires as a way of warming the place up a bit. 

[rusty69]

23 minutes ago, magnetman said:

In the thread I found on the solar forum someone said you can calibrate the sensor on the BMS. 

Sooo. It looks like the temp can be adjusted. You sir are a genius. 

 

Thank you 

[cuthound]

6 hours ago, magnetman said:

An infrared thermometer is a good toy. 

 

You could point it at one sensor then the other and see if they are the same temperature. 

 

And you can check its calibration using a pan of boiling water (unless you live on a high mountain top or a long way below sea level).

[rusty69]

42 minutes ago, cuthound said:

 

And you can check its calibration using a pan of boiling water (unless you live on a high mountain top or a long way below sea level).

Actually, I recall now thatI tried testing my IR themometer with the intention of callibrating it. I pointed it at boiling water, my body and a block of ice. Confused by the results (no, i'm not dead), I approached the manufaturers of said instrument to clarify the results. They advised me that one cannot meaure water temperature accurately with an IR thermometer.

 

Here is what they said:

Quote

Infrared Thermometers CANNOT measure water temperature accurately.

 

The reason being is that liquid absorbs Infrared rays. As also Glass will.

 

The emissivity of the instrument is pre-set @ 0.95. Emissivity is effected by the colour of the surface being measured and its ability to absorb and emit radiated heat.

 

Edited November 30, 2023 by rusty69

[cuthound]

7 minutes ago, rusty69 said:

Actually, I recall now thatI tried testing my IR themometer with the intention of callibrating it. I pointed it at boiling water, my body and a block of ice. Confused by the results (no, i'm not dead), I approached the manufaturers of said instrument to clarify the results. They advised me that one cannot meaure water temperature accurately with an IR thermometer.

 

Here is what they said:

 

 

Point it at the side of the pan near the surface of the water.

[rusty69]

Just now, cuthound said:

 

Point it at the side of the pan near the surface of the water.

Ok. Any idea where I put it? 

[Tony1]

9 minutes ago, rusty69 said:

Actually, I recall now thatI tried testing my IR themometer with the intention of callibrating it. I pointed it at boiling water, my body and a block of ice. Confused by the results (no, i'm not dead), I approached the manufaturers of said instrument to clarify the results. They advised me that one cannot meaure water temperature accurately with an IR thermometer.

 

Here is what they said:

 

 

I had some serious problems with emissivity,  but that was after a bad curry. 

I was a bit preoccupied to measure with accuracy, but it certainly reached level 8 (aka "f*ck, just let me die"). 

 

 

[magnetman]

37 minutes ago, rusty69 said:

Ok. Any idea where I put it? 

Someone borrowed it. I think it was Fred. 

[rusty69]

Fred drift?

[magnetman]

I think so. He is a cousin of Fogstar Drift. 

[nicknorman]

It's a shame these BMSs use thermistors (often referred to as an "NTC") for temperature measurement. They are not particularly accurate. For about 50p in bulk, one could use a digital one-wire sensor like a DS1822 or equivalent, accurate to around 0.5C with no need for calibration.

[cuthound]

1 hour ago, rusty69 said:

Ok. Any idea where I put it? 

 

Have you looked down the back of the sofa. I've found lots of things I thought I'd lost there.

[TheBiscuits]

2 hours ago, rusty69 said:

Any idea where I put it? 

 

That's the trouble with infrequently read thermometers. If it was used more often you'd know where it was.

 

When I was looking for mine, MrsBiscuit thought it was funny to say "You're getting warmer" as I approached the correct locker!