Wiring a battery monitor shunt

[Glandwr]

Hi planning one neg from battery to shunt input (battery side) and then as indicated all "load negs" from the output.

I'm assuming that temp sensors for the EBL and B2B are NOT load negs. But all others including solar, EBL, inverter Actual B2B are. Is that correct?

 

[1 Cup]

My Thinking ! all negatives go to shunt . Mite need a bus bar or 2 on that side. Battery from otherside.

 

[Glandwr]

My Thinking ! all negatives go to shunt . Mite need a bus bar or 2 on that side. Battery from otherside.

Even the battery temp sensor? Come to think of it if the battery has a BMS do we need the old temp sensor to the B2B?

 

[merl]

Technically ALL negative supplies should go to the battery neg terminal via the shunt but in reality any device that takes minimal current won't have a significant effect on consumption so could be wired directly to the battery. If it's relatively simple to be do so just let everything go via the shunt.

 

[1 Cup]

Even the battery temp sensor? Come to think of it if the battery has a BMS do we need the old temp sensor to the B2B?

If you like parasites drain all mine go through then I calibrated the shunt. So it zero it.

 

[merl]

Even the battery temp sensor? Come to think of it if the battery has a BMS do we need the old temp sensor to the B2B?

If the temperature sensor is performing temperature compensation of the charge voltage then no, generally temp comp is considered unnecessary with lifepo4..

 

[wildebus]

If the temperature sensor is performing temperature compensation of the charge voltage then no, generally temp comp is considered unnecessary with lifepo4..

You might want to add it to a setup where you don't have full confidence in the batteries BMS to shut off cold-temp charging however so you can more accurately disable the chargers to prevent potential damage at too-low temps

Ideally you want a Lithium Battery to have that low-temp charging control built-in though (and even more ideally, integral heating pads) rather than disabling the chargers as that charging power can be usefully employing to supplement the battery power rather than just losing it entirely.

 

[Glandwr]

You might want to add it to a setup where you don't have full confidence in the batteries BMS to shut off cold-temp charging however so you can more accurately disable the chargers to prevent potential damage at too-low temps

Ideally you want a Lithium Battery to have that low-temp charging control built-in though (and even more ideally, integral heating pads) rather than disabling the chargers as that charging power can be usefully employing to supplement the battery power rather than just losing it entirely.

The sensor is I think a high temp one fitted to stop the B2B boiling the old sealed lead batteries. It was fitted 2014 well before LifePo4 and its cold temp eccentricities was known. Think I'll get rid of it unless someone says Whoa!

 

[merl]

The sensor is I think a high temp one fitted to stop the B2B boiling the old sealed lead batteries. It was fitted 2014 well before LifePo4 and its cold temp eccentricities was known. Think I'll get rid of it unless someone says Whoa!

Impossible to judge unless we know exactly what type of sensor it is and how it functions.
Most likely? a thermistor (temperature dependent resistor) that links to internal electronics, but could be a simple bi metallic switch that opens/closes at a preset temp either hi or low. The lifepo4's should have an inbuilt low temp charge cut off but unless you're willing to spend the time and effort getting your batteries down to near zero and seeing what happens to the BMS you'll not know it's existence or effacacy so largely that's a case of fit and cross fingers! If the sensor is external and you have the interest/will/ arse you could remove it and put it in a fridge/ freezer/ and measure with a ohmeter. If it is a low temp cuttoff type you could possibly add it to the new setup to offer additional protection from low temp charging.

 

[wildebus]

Impossible to judge unless we know exactly what type of sensor it is and how it functions.
Most likely? a thermistor (temperature dependent resistor) that links to internal electronics, but could be a simple bi metallic switch that opens/closes at a preset temp either hi or low. The lifepo4's should have an inbuilt low temp charge cut off but unless you're willing to spend the time and effort getting your batteries down to near zero and seeing what happens to the BMS you'll not know it's existence or effacacy so largely that's a case of fit and cross fingers! If the sensor is external and you have the interest/will/ arse you could remove it and put it in a fridge/ freezer/ and measure with a ohmeter.

I think the newer cheap batteries now tend to have BMSes that are actually able to prevent low-temp charging, but I would be wary about how to check that. Maybe put the battery into a fridge and connect to a very low current charge and see it if disconnects at a set point?

If it is a low temp cuttoff type you could possibly add it to the new setup to offer additional protection from low temp charging.

The chances are a different device will need a different temp sensor as there are quite a few types around, all with their own calibrations. As an example, for some reason Victron use a different temp sensor on their BMV Monitors to their Multiplus Chargers. No idea why and the two different ones LOOK identical, but Victron are very careful to point out they are different.

 

[merl]

I think the newer cheap batteries now tend to have BMSes that are actually able to prevent low-temp charging, but I would be wary about how to check that. Maybe put the battery into a fridge and connect to a very low current charge and see it if disconnects at a set point?


The chances are a different device will need a different temp sensor as there are quite a few types around, all with their own calibrations. As an example, for some reason Victron use a different temp sensor on their BMV Monitors to their Multiplus Chargers. No idea why and the two different ones LOOK identical, but Victron are very careful to point out they are different.

Yeh, I know,, the amount of different values of thermistor AND the fact that there are 2 different types PTC and NTC makes them pretty much individual for each use. There's usually a 5-10 fold markup on them when you buy them as a branded accessory as opposed to getting them from CPC or farnell, problem is unless you've got an example you simply don't know what value you need! (Come to think of it David....)
To be honest I was thinking IF the sensor was a simple bi-metalic type ( which if it was originally for temp comp it won't be!) that opened at around zero then it could be fitted in the D+ line supplying the B2B, sort of adding a 'just in case' layer of protection.