Shunt vs Hall Sensor battery monitors

[Flyview]

Hey everyone!

I'm new here. I have a Sportsmobile with a 12V 200Ah LiFePO4 system and a 100W solar panel. I'd like to buy a battery monitor so I can see current draw and/or current charge on my battery bank. Right now the system just has a simple voltmeter on it which doesn't tell me much in terms of current.

I've been looking through Amazon and the choices are making me dizzy. I've noticed there are shunt style and Hall effect sensor style battery monitors. Some shunt battery monitors only monitor current in one direction (requiring you buy 2?), while some are bidirectional. Are there any advantage to one style over the other? Can both measure battery capacity as well as current?

It seems to me the Hall effect battery monitors would be way easier to set up as you just have to clamp around the battery bank's main negative (or positive?) cable.

Thoughts? Recommended battery monitors?

Shunt battery monitor example
Hall effect battery monitor example

Thanks!

 

[Markus]

I was just going to post the same. I would like everyone's suggestion as well.

 

[Bob142]

I have an AiLi shunt in two of my systems and a Drok hall effect in another. For me the shunt wins hands down. The hall effect style gives readings that are much less accurate and reliable.

@SCClockDr has posted about this in the past regarding using hall effect sensors in vehicles:

SOC meter that uses amperage acceptance instead of voltage?

Voltage is a terrible way to keep track of SOC unless you're already deep into the 'knees' and if thats what you're trying to avoid its already too late. I suppose if you had a really LARGE bank the inputs and outputs would still keep the C rate low enough its would be sorta accurate without...

diysolarforum.com

 

[newbostonconst]

I am really enjoying my Victron BMV-700 series. It is blue tooth so can monitor through phone and seems extremely accurate. Is bi directional and keeps state of charge at all times. Has history about amount of power used and amount needed to charge.

 

[Flyview]

I was just going to post the same. I would like everyone's suggestion as well.

I've been researching this since last night and here's what I've noticed:

All the DC 100A Hall Effect battery monitors are only precise to 1 decimal point or 0.1A, whereas the shunts show 2 decimal points, 0.01A. So they may be more accurate. In a 12V lithium system, 0.1A is about 1.3W, so if you want to see draws/charges more precise than that go with shunt.

Here's a cool little paper from Texas Instruments discussing the differences between shunt based and Hall effect based sensing when it comes to EV applications:

http://www.ti.com/lit/an/sbaa293b/sbaa293b.pdf?ts=1588263168548

They mention that traditionally shunts are preferable for <50A, more stable over different temperatures, aren't influenced by EM noise, etc.

I have an AiLi shunt in two of my systems and a Drok hall effect in another. For me the shunt wins hands down. The hall effect style gives readings that are much less accurate and reliable.

@SCClockDr has posted about this in the past regarding using hall effect sensors in vehicles:

SOC meter that uses amperage acceptance instead of voltage?

Voltage is a terrible way to keep track of SOC unless you're already deep into the 'knees' and if thats what you're trying to avoid its already too late. I suppose if you had a really LARGE bank the inputs and outputs would still keep the C rate low enough its would be sorta accurate without...

diysolarforum.com

How have you tested that the Drok Hall Effect readings are much less accurate and reliable? By how much?

As for me, I'm still trying to decide. I don't think I really care about the increased accuracy down to 0.01A, but I also don't want the readings to drift or be affected by magnetic fields in my van, etc. I'm leaning towards the Hall effect style just based on how easy it will be to install.

 

[loverofpeace]

I have an AiLi shunt in two of my systems and a Drok hall effect in another. For me the shunt wins hands down. The hall effect style gives readings that are much less accurate and reliable.

@SCClockDr has posted about this in the past regarding using hall effect sensors in vehicles:

SOC meter that uses amperage acceptance instead of voltage?

Voltage is a terrible way to keep track of SOC unless you're already deep into the 'knees' and if thats what you're trying to avoid its already too late. I suppose if you had a really LARGE bank the inputs and outputs would still keep the C rate low enough its would be sorta accurate without...

diysolarforum.com

Did you have to buy two or was it a dual one? That measures incoming and outgoing current?

 

[Bob142]

Did you have to buy two or was it a dual one? That measures incoming and outgoing current?

Just one. The AiLi's are bidirectional.

 

[Glenn Dale]

I was just going to post the same. I would like everyone's suggestion as well.

I just installed the AiLi Battery Meter. Works well.

 

[Bob142]

How have you tested that the Drok Hall Effect readings are much less accurate and reliable? By how much?

As for me, I'm still trying to decide. I don't think I really care about the increased accuracy down to 0.01A, but I also don't want the readings to drift or be affected by magnetic fields in my van, etc. I'm leaning towards the Hall effect style just based on how easy it will be to install.

I put some info in my Yeti 1250 thread a while ago. Since then what I've noticed is that it seems to read phantom current depending on where the Yeti is located and will falsely indicate that the battery has discharged fairly substantially during periods when the system is idle.

The only reason I didn't go with a shunt in that system is that it's a tight space that makes it difficult to install one. I highly recommend you go the shunt route. They aren't that difficult to install and are well worth it.

 

[Flyview]

I put some info in my Yeti 1250 thread a while ago. Since then what I've noticed is that it seems to read phantom current depending on where the Yeti is located and will falsely indicate that the battery has discharged fairly substantially during periods when the system is idle.

The only reason I didn't go with a shunt in that system is that it's a tight space that makes it difficult to install one. I highly recommend you go the shunt route. They aren't that difficult to install and are well worth it.

Thanks! I think you're right. Very helpful that you have the exact one I was going to buy. Right now I have 2 100Ah lithium batteries connected in parallel. There's a ground cable from the first battery to the second and a ground cable from the second battery to the chassis. I can probably bolt the shunt straight to the second battery negative and then bolt the cable back onto the other side of the shunt going to the chassis ground. I will probably go with the AiLi Battery Meter like everyone else, but what do you guys think of this one? Hah, just noticed this one is also by AiLi...

 

[Fred S]

I've had both kinds and both were accurate. Bidirectional capability is handy, but not common on cheap meters. Cheap doesn't necessarily mean bad though. What you can do is get two cheap shunt-style meters that aren't bidirectional, and let them share the same shunt. You reverse the shunt pickup wires for the 2nd meter. Meter #1 reads amps for one direction, and the 2nd meter reads zero. When the current reverses, the 2nd meter reads amps while the 1st reads zero. If the meters do any tallying, say hours or watt-hrs, you'll then have a separate tally for charging and discharging.

 

[xjaywalker]

I just installed the AiLi Battery Meter. Works well.

Hi Glen...Question on your install of the AiLi BMS..It comes with around 7 ft of wire and I was hoping to route mine up inside the RV (I would need another 4ft of wire) Where did you mount yours?

 

[BoloMKXXVIII]

You might want to check this out:

PowerMon - Bluetooth LE Advanced Battery Monitor / DC Power Meter with data logging

We developed the PowerMon device to provide an affordable, high-tech solution for monitoring electrical systems. Whether you're in an RV, camper, or boat, utilizing solar systems, or managing off-grid setups, PowerMon is designed to meet your battery monitoring needs. Remotely monitoring DC...

www.thornwave.com

A bit more money, but very versatile.

 

[JDunn]

BoloMKXXVIII, I have the Thornwave BMDC protecting my 24v Valence lithium pack and monitoring my 12v RV house bank and love it. O/U voltage protection, O/current protection and Temp sensing with bluetooth for only $120 on the website. The ability to add an external shunt really allows this to grow with your system. I've emailed with Razvan and he's been very responsive and helpful with my questions.

 

[Flyview]

I wanted to update on what I ended up doing. I bought this AiLi shunt battery monitor with the red LCD display. It is bidirectional and I like how it can display 2 different things at once, and how you can turn the display off. I had to make my own cable to connect 5 wires to its inputs (2 current sensing on either side of the shunt, 2 for voltage) which I did out of an old ethernet cable.

The only bad thing I've noticed is that it is a bit temperature dependent. With nothing connected to the battery except the shunt, the current draw varies by about +/- 4W within a temp range of 10c (estimation), showing more current draw as it gets colder and less current draw as it gets hotter. I guess if you reset it at a midway temperature that will average itself out. Has anyone else seen this?

 

[RCinFLA]

A hall effect sensor for battery DC current should not be used unless it is a closed loop hall effect sensor. I can pretty much assure that any hall effect sensor sold on Alibaba or eBay is not a closed loop hall effect sensor as they are expensive.

An open loop hall effect sensor measuring high D.C. current will likely develop magnetic core bias that will change its accuracy significantly over time. Large surge currents will make magnetic bias worse.

A closed looped hall effect sensor has a power op amp that feeds a large turns ratio counter field coil. This keeps the magnetic field in the core at a very low level preventing magnetic core bias. The op amp requires external DC power supply, typically +/-12 to +/- 15vdc.

Stick with a good quality shunt. Keep in mind the potential heat generated at high current. For a 300A for 75 mV shunt that is max of 300A x 0.075v = 22.5 watts of heating. A good quality shunt has mixed metal alloys for the shunt resistance that is near zero temperature coefficient so it doesn't change resistance much with temperature. Most higher end battery monitors from quality companies use 50 mV shunts, especially for 500A shunts.

Shunts in BMS's are just copper PCB runner, copper strap, or short piece of wire so don't count on good accuracy.