Internally Heated Battery Monitoring

[SolarN00Bie]

Hi everyone, I'm new here and planing my first solar setup on my vehicle. The intent is to have a setup similar to Dan Grec but with an internally heated lithium house battery. I want to use the Renogy DC-DC MPPT controller connected to a solar panel, starter battery, and house battery and have it be displayed on a monitor (wired). Here is where my concern begins (probably due to a lack of knowledge). While reading the literature from Battle Born on their heated batteries I read this on page 7:
In what scenerio would this statement be accurate and is there a way to be able to keep an accurate measurment of how much power is left in the battery?

My thought is if the accessories such as the fridge and lights are connected to the house battery, then the house battery is connected to the Renogy DC-DC controller, and then displayed via a monitor potentially such as this one connected at the charge controller there should not be any issues accurately displaying the charge. I wouldn't be able to differentiate when the heater is on or off but it should still see it charging and discharging none the less. Am I incorrect with these thoughts or should it work?

Thank you!

 

[sunshine_eggo]

The monitor you linked has no useful value in monitoring a battery state of charge. It's simply an interface with the DC-DC charger. The monitors of which they speak are the shunt type that measure current in and out of a battery and compute a true state of charge, i.e., the "BMV" they mention would be a BMV-700/702/712 or a Smartshunt.

Speaking in the context of a "BMV" type monitor, if the battery is in heating mode, it will allow incoming current, but it will divert that current to the heater rather than charging. An external monitor can only see the incoming current and can have no possible way of knowing it's not being used for charging.

In that case, the monitor will register an increase in state of charge that's not actually happening. It will show 100% prematurely.

There's nothing you can do about this. The good news is that the next time the battery is fully charged, the properly configured monitor will "recalibrate" to true 100% and will accurately reflect state of charge.

 

[SolarN00Bie]

The monitor you linked has no useful value in monitoring a battery state of charge. It's simply an interface with the DC-DC charger. The monitors of which they speak are the shunt type that measure current in and out of a battery and compute a true state of charge, i.e., the "BMV" they mention would be a BMV-700/702/712 or a Smartshunt.
Then why does the description of the monitor say "Dual Battery Monitoring: Stay informed about your house and auxiliary battery's charging status and easily monitor the solar system's overall health."? Where would it get this information except for through the DC-DC charge controller?
Speaking in the context of a "BMV" type monitor, if the battery is in heating mode, it will allow incoming current, but it will divert that current to the heater rather than charging. An external monitor can only see the incoming current and can have no possible way of knowing it's not being used for charging.
This is what I've been also hearing from others who I've been talking to.
In that case, the monitor will register an increase in state of charge that's not actually happening. It will show 100% prematurely.
I absolutely do not want misleading data.
There's nothing you can do about this. The good news is that the next time the battery is fully charged, the properly configured monitor will "recalibrate" to true 100% and will accurately reflect state of charge. There's no fancy work around for this? This is unfortunately what others have told me too.

First off, thank you for taking the time to help me out. This definitely helps clarify things in my head. I have replied to your statements in red above. I have looked into standard self heated batteries with the downsides you have described. I also looked into the Renogy smart self heated battery. I could hook a monitor directly to the Renogy battery and get accurate data that way but would require a second monitor for other system information. Also a downside to the Renogy heating function is that it requires a charge going to it to activate the heating, otherwise it just won't heat. So I don't like either of these two options. I think so far the best idea I can come up with is to use the Roamer Xtreme battery from the UK. It uses special low temperature cells to work up to -40F without heating. I'll just have to find a way to get it to the USA (which I might know a way).

 

[mikefitz]

The Renogy monitoring screen operates only with the Renogy chargers and battery information relates to battery voltage, charge currents and a totally inaccurate SOC for the house battery. It cannot compute actual current Into and out from the house battery and thus cannot provide accurate SOC.
The Victron BMV series and Victron Smart shunt have a current monitoring device, a shunt, in the battery negative path.

Your concern regarding heated batteries may be over reacting. Although charging cannot take place below 0C the batteries can deliver power down to -20C. Since the batteries will be in a vehicle with you, hopefully the temperature will be above 0C.
One technique to heat the batteries is to use heating pads, these are powered from the 12v system, not internal battery energy , thus a BMV type monitor will be accurate, regarding SOC.

You Dan Grec is advertising and generating income, his electrical ability as shown in the video, did not follow best ptactice, example undersized cables.

Lithium cells can be engineered to charge lower than 0C, for example Winston cells, but the charge current is limited at low temperatures.
It's also clear from the published texts carries out be Roamer Batteries that charging at low temperature is carried out at a lower current and that the effective capacity, when charged at low temperature, was lower than nominal.

 

[sunshine_eggo]

First off, thank you for taking the time to help me out. This definitely helps clarify things in my head. I have replied to your statements in red above. I have looked into standard self heated batteries with the downsides you have described. I also looked into the Renogy smart self heated battery. I could hook a monitor directly to the Renogy battery and get accurate data that way but would require a second monitor for other system information. Also a downside to the Renogy heating function is that it requires a charge going to it to activate the heating, otherwise it just won't heat. So I don't like either of these two options. I think so far the best idea I can come up with is to use the Roamer Xtreme battery from the UK. It uses special low temperature cells to work up to -40F without heating. I'll just have to find a way to get it to the USA (which I might know a way).

When you reply to comments, please place an enter after the text to which you are replying making your reply YOUR text, otherwise my reply to your reply cuts all that out.

My answers to your questions:

Marketing

On a separate device that tracks true state of charge like a Victron Smartshunt - a device analogous to the "BMV" referenced.

You can't avoid the bad data. As I mentioned, the good news is that the next time the battery is truly fully charged, the "BMV" will recalibrate to the correct 100%, and it would remain accurate until the heaters are used again.

 

[SolarN00Bie]

The Renogy monitoring screen operates only with the Renogy chargers and battery information relates to battery voltage, charge currents and a totally inaccurate SOC for the house battery. It cannot compute actual current Into and out from the house battery and thus cannot provide accurate SOC.
The Victron BMV series and Victron Smart shunt have a current monitoring device, a shunt, in the battery negative path.

Gotcha, that makes sense. It's not what I'm looking for then.

Your concern regarding heated batteries may be over reacting. Although charging cannot take place below 0C the batteries can deliver power down to -20C. Since the batteries will be in a vehicle with you, hopefully the temperature will be above 0C.
One technique to heat the batteries is to use heating pads, these are powered from the 12v system, not internal battery energy , thus a BMV type monitor will be accurate, regarding SOC.

Even though it charges slower it does still charge and that's important to me as I live in a place and travel to places that get quite cold. I do think I would put a heating pad on it too.

You Dan Grec is advertising and generating income, his electrical ability as shown in the video, did not follow best ptactice, example undersized cables.

Lithium cells can be engineered to charge lower than 0C, for example Winston cells, but the charge current is limited at low temperatures.
It's also clear from the published texts carries out be Roamer Batteries that charging at low temperature is carried out at a lower current and that the effective capacity, when charged at low temperature, was lower than nominal.

I missed that part of their literature so thanks for that. I'll re-read it. I bought Will Prowse's book so I'll e sure to follow his guidelines for proper gauging.

Thanks for the response!

 

[SolarN00Bie]

When you reply to comments, please place an enter after the text to which you are replying making your reply YOUR text, otherwise my reply to your reply cuts all that out.

Gotcha!

My answers to your questions:

Marketing

Makes total sense under that perspective

On a separate device that tracks true state of charge like a Victron Smartshunt - a device analogous to the "BMV" referenced.

You can't avoid the bad data. As I mentioned, the good news is that the next time the battery is truly fully charged, the "BMV" will recalibrate to the correct 100%, and it would remain accurate until the heaters are used again.

It recalibrating would be nice but to me having accurate informaton is more important so I will look for another way of doing things.

Thank you!

 

[sunshine_eggo]

It recalibrating would be nice but to me having accurate informaton is more important so I will look for another way of doing things.

If you figure it out, you need to market it because no one else has a solution. There's a reason BB is issuing a warning rather than a solution for more $. I really don't think you understand what is happening and the implications or you wouldn't have this inflexible view demanding accurate data when it's near impossible or at least more difficult than it's worth.

You have a sealed box. Inside that box current either goes to adding charge or goes to heating the battery. There is no means of communicating what is happening to a device mounted to the battery terminal monitoring current in and out of the battery.

Shunts are designed to recalibrate each and every time the system is fully charged, and they must do so fairly regularly, or their accuracy will deteriorate.

 

[Tomthumb62]

Get any decent lifepo4 battery WITHOUT a self heating feature but does have low temp protection. Then wire external heat pads to the outside of the battery wired with an external temp controller. There are posts on this forum with details how. And Will Prowse has a video on it. Make sure the heating pads are connected to the monitoring shunt to record the energy used. Then you’ll be as accurate as possible in the battery SoC.

Second, consider if you truly need any battery heating at all. Will Prowse made a video recently about how he thinks most people don’t actually need this but are sold on marketing that they do. As long as your battery has low temperature charging cutoff protection, your battery will be protected from damage. Now if the battery actually gets cold enough to trigger that protection, it won’t accept charging until it warms up enough. So that warmth needs to come from the ambient air or heating pads. Keep your van warm enough (above freezing) and you’ll be golden. INSULATE YOUR VAN!!

SOK makes a good battery. They have models with and without internal heating but both have low temperature protection. Battle born is overpriced IMO.

Finally, most battery chemistries, including lifepo4 will operate at reduced power and current in really cold temperatures. If you intend to live in your van at -20F or colder, be sure to insulate your battery to help it stay warmer. As the battery charges or discharges, it will stay warmer from those processes.