Bluetooth Smart Battery Monitor

[carlsbad]

Originally Posted by babock

Doesn't even look like it's wired up correctly to measure current. Should have the negative battery post wired to the input of the shunt and the output going to the trailer. The fact that there are two leads on the battery means it can't measure current properly.

Aren’t you just a bundle of joy.

[babock]

Originally Posted by carlsbad

Aren’t you just a bundle of joy.

Why don't you read post #4.

You should post in some other threads you dont care about.

[TitanMike]

Originally Posted by garbonz

Kinda like a Victron bmv700 without the readout. Brilliant idea, although many would want a external shunt to handle larger gauge wire and higher current. The Victron with Bluetooth monitor is double that price, and the trimetric doesn't have Bluetooth I don't think.

Good post.

After reading the description and specs, it's a lot like the Victron, just stripped of the display and shunt.

Their smartphone app replaces the display and for units that don't have big inverters or large converters, where current flow can exceed 60 amp this looks like a great value.

I think the Victron provides more data such as time remaining to set soc level but it appears that the basics are there.

A good find.

[babock]

Originally Posted by TitanMike

After reading the description and specs, it's a lot like the Victron, just stripped of the display and shunt.

Not sure if I saw anywhere in the specs where you can enter a Peukert constant. Not sure how accurate it will be without that over time.

[Alben]

A lot of good points being brought up.

Yes, I am somewhat concerned that I have it installed inside the battery box instead of inside the trailer, which would a much better location as it would be a dry and corrosion free environment. The module does appear to be completely potted. But I do suppose corrosion could happen to the screw terminals. I may move it inside the trailer and so some minor rewiring of the trailer to bring the feed of the battery into the trailer, through the battery monitor, and back out under the trailer.

Yes, I too have a basic DC voltmeter that I installed by the radio, which is useful for basic state of charge. Actually I published a complete writeup of my addition of a DC power panel to this forum fall 2017. As others have noted, a basic DC voltmeter is only accurate when there is no current draw.

My main motivation of installing the Bluetooth Smart Battery Monitor was to see what happens when towing my trailer and running the fridge on 12VDC. I just towed my trailer 4 hours one way to a state park last week while running my fridge on 12VDC. I monitored the trailer battery from within the tow vehicle. I was surprised that my tow vehicle (see signature) was able to provide the entire demand current of the fridge. There was absolutely no drain from the trailer battery. We also stopped for a 15 minute rest stop, which resulted in a drain from the trailer battery. When resuming towing after the rest stop, the tow vehicle kept supplying the fridge current AND actually charged the trailer battery. I was actually surprised.

I would like to do a test sometime with the trailer battery discharged to 50% and the fridge running and see how much recharge of the trailer battery could be accomplished. I don't have much faith in getting much recharge, but it would be interesting to know.

[TitanMike]

Originally Posted by Alben

I would like to do a test sometime with the trailer battery discharged to 50% and the fridge running and see how much recharge of the trailer battery could be accomplished. I don't have much faith in getting much recharge, but it would be interesting to know.

I monitored my battery bank, although not on a A-frame over a month long trip. I found that while charging did take place while driving it was at a pretty low rate. Limiting factor is wire size from tow vehicle battery to trailer connector. The woltage drop makes the vehicle alternator think battery is close to fully charged and lowers voltage to more of an absorption rate than bulk charge rate. There might be enough to cover the overhead of the refrigerator but don't expect a huge gain in soc unless you drive for 8-10 hours.

Upgrading the charging wire in the TV to a much larger wire would improve that.

[pgandw]

Originally Posted by babock

A voltage meter is useless unless there is zero load and really only accurate after no load for 20 minutes. It's also useless to determine what that actual current load is or how much current is going into the batteries either from your converter or solar controller.

Totally disagree. "Useless" is in the eyes and opinion of the beholder. The voltmeter tells me what stage the converter is in when the converter is charging. The converter charge voltage tells me where the converter thinks the batteries are. The voltmeter also tells me how well I am (or am not) charging the A-frame batteries while towing with fridge on DC and running lights on/off.

Since the battery loads are low current while camping in an A-frame, the voltage approximation of the battery state is surprisingly accurate once charge has been removed for a few hours.

The shunt resistor used to measure current in/out of the battery has to be very precise to get an accurate current in/out of the battery. 1% of 0.001 or even 0.01 ohms doesn't allow much manufacturing or connection tolerance before the measurements are thrown off. And since you only have a manufacturer's design claim for actual battery capacity, the calculation of battery state is not likely to be any more accurate than my voltmeter.

The one good thing you do get from continuous current monitoring is accurate AH in or out of the battery.

But as I said in my post, I don't camp to monitor my batteries. I just want to get up in the morning, check the battery voltage, and be able to determine whether or not I need to do something to recharge the batteries before another night transpires. When plugged in, I want to check that the converter is properly doing its thing. The voltmeter performs these functions very inexpensively compared to a battery monitor system.

My batteries were calculated to run the A-frame for 4 nights dry camping with max 5hrs heater use at night, none during the day, without dropping below 50%. The voltmeter gives me a rough idea of how I am doing against the calculations, which is all I ask.

Fred W
2014 Rockwood A122 A-frame, dual GC-2 Interstate batteries from Costco
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[babock]

Originally Posted by pgandw

Totally disagree. "Useless" is in the eyes and opinion of the beholder. The voltmeter tells me what stage the converter is in when the converter is charging. The converter charge voltage tells me where the converter thinks the batteries are. The voltmeter also tells me how well I am (or am not) charging the A-frame batteries while towing with fridge on DC and running lights on/off.

Since the battery loads are low current while camping in an A-frame, the voltage approximation of the battery state is surprisingly accurate once charge has been removed for a few hours.

The shunt resistor used to measure current in/out of the battery has to be very precise to get an accurate current in/out of the battery. 1% of 0.001 or even 0.01 ohms doesn't allow much manufacturing or connection tolerance before the measurements are thrown off. And since you only have a manufacturer's design claim for actual battery capacity, the calculation of battery state is not likely to be any more accurate than my voltmeter.

The one good thing you do get from continuous current monitoring is accurate AH in or out of the battery.

But as I said in my post, I don't camp to monitor my batteries. I just want to get up in the morning, check the battery voltage, and be able to determine whether or not I need to do something to recharge the batteries before another night transpires. When plugged in, I want to check that the converter is properly doing its thing. The voltmeter performs these functions very inexpensively compared to a battery monitor system.

My batteries were calculated to run the A-frame for 4 nights dry camping with max 5hrs heater use at night, none during the day, without dropping below 50%. The voltmeter gives me a rough idea of how I am doing against the calculations, which is all I ask.

Fred W
2014 Rockwood A122 A-frame, dual GC-2 Interstate batteries from Costco
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

It's useless unless there is zero load to calculate SOC. I stand by my statement.

This thread is a about a battery monitor. No need to hijack it.

[Bluepill]

The discussion about usefulness really depends on expectations. Same arguments can be made about an auto with an actual ammeter vs. the Idiot Light.

One gives more information, but must be monitored. The other just screams for attention when it thinks there is a problem.

Different strokes.........

[TitanMike]

Originally Posted by Bluepill

The discussion about usefulness really depends on expectations. Same arguments can be made about an auto with an actual ammeter vs. the Idiot Light.

One gives more information, but must be monitored. The other just screams for attention when it thinks there is a problem.

Different strokes.........

I'm wondering if it's more a case of "If you don't use what I use then yours is no good".

The term "useless" is improperly applied here. If it's telling the owner what he wants to know then to him it's extremely useful.

Funny thing, some people with smaller trailers that use the battery mainly to keep a light or two in before going to bed, run the water pump, and keep the refrigerator going are often happy to just recharge the battery when the light goes dim, the pump slows down, or the refrigerator won't light off. They then just spend the money on another relatively inexpensive group 24 marine battery rather than a couple hundred or more on a battery monitor that gives them more data than they care about.

When one's trailer is just one step up from a tent, just how much technology does one really need. I'm speaking in the generic sense.

[carlsbad]

Originally Posted by TitanMike

I'm wondering if it's more a case of "If you don't use what I use then yours is no good".



The term "useless" is improperly applied here. If it's telling the owner what he wants to know then to him it's extremely useful.



Funny thing, some people with smaller trailers that use the battery mainly to keep a light or two in before going to bed, run the water pump, and keep the refrigerator going are often happy to just recharge the battery when the light goes dim, the pump slows down, or the refrigerator won't light off. They then just spend the money on another relatively inexpensive group 24 marine battery rather than a couple hundred or more on a battery monitor that gives them more data than they care about.



When one's trailer is just one step up from a tent, just how much technology does one really need. I'm speaking in the generic sense.

Every small camper needs a Binford 2000 NIST-calibrated Bluetooth monitor with a shunt accurate to the picoamp. God forbid the light puts out a few less lumens. Arr arr arr!

Don’t forget your 1-ton dually. These things are heavy!

[babock]

So the ironic thing is that the the OP starts the thread about his Bluetooth monitor and explained why he chose to install it and the voltage meter people are the ones hopping on and saying he should just use a voltage meter.

[pgandw]

Originally Posted by babock

So the ironic thing is that the the OP starts the thread about his Bluetooth monitor and explained why he chose to install it and the voltage meter people are the ones hopping on and saying he should just use a voltage meter.

And you are busy trying to control the thread...claiming to benefit the OP.

FWIW, I took some measurements last night and this morning on my A-frame. We went camping last weekend, so the A-frame was set up in the garage, on trickle charge (13.2V). I disconnected the batteries (no load at all on dual Costco 232AH GC-2 bought in 2015) and waited 75 minutes. 13.13V at the battery posts. Obviously, the batteries were going to take while to get to normal state after being removed from the charger without any load.

This morning, got up before work and took measurements. 11 hours 15 minutes since disconnect. 12.87V. Still a little high, but could be meter error as well as surface charge. Turned on the Fantastic Fan to add some load, and reconnected the batteries. 12.82V while powering Fantastic Fan (on low), propane/CO detector, and any parasitic draw from the electronic thermostat for heater/AC and water heater control board (both turned off). This is normal camping load for us when heater is not running. I had installed a switch on both stereo power leads, so no parasitic draw there.

Disconnected the batteries - 12.84V. Reconnected batteries with same load - 12.82V. Disconnected batteries - 12.84V. One more cycle with same readings, so I quit.

My conclusions: small loads do not significantly impact the use of voltage to estimate SOC. However, unloaded batteries take a long time to reach "correct" voltage reading when removed from a charger. The 12 hour rule is not out of line. I assume that any load will speed this process considerably, but will need further experimentation to confirm.

just my experiences
Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[babock]

Originally Posted by pgandw

And you are busy trying to control the thread...claiming to benefit the OP.

FWIW, I took some measurements last night and this morning on my A-frame. We went camping last weekend, so the A-frame was set up in the garage, on trickle charge (13.2V). I disconnected the batteries (no load at all on dual Costco 232AH GC-2 bought in 2015) and waited 75 minutes. 13.13V at the battery posts. Obviously, the batteries were going to take while to get to normal state after being removed from the charger without any load.

This morning, got up before work and took measurements. 11 hours 15 minutes since disconnect. 12.87V. Still a little high, but could be meter error as well as surface charge. Turned on the Fantastic Fan to add some load, and reconnected the batteries. 12.82V while powering Fantastic Fan (on low), propane/CO detector, and any parasitic draw from the electronic thermostat for heater/AC and water heater control board (both turned off). This is normal camping load for us when heater is not running. I had installed a switch on both stereo power leads, so no parasitic draw there.

Disconnected the batteries - 12.84V. Reconnected batteries with same load - 12.82V. Disconnected batteries - 12.84V. One more cycle with same readings, so I quit.

My conclusions: small loads do not significantly impact the use of voltage to estimate SOC. However, unloaded batteries take a long time to reach "correct" voltage reading when removed from a charger. The 12 hour rule is not out of line. I assume that any load will speed this process considerably, but will need further experimentation to confirm.

just my experiences
Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

I appreciate you proving my point.

[pgandw]

Originally Posted by babock

It's useless unless there is zero load to calculate SOC. I stand by my statement.

I proved the opposite of your point. The voltage drop with a typical A-frame load attached is insignificant in determining approximate SOC with a voltmeter, as shown by my experiment. My practice of checking battery voltage in the morning when I get up while camping is proven sufficient.

Using a voltmeter to determine SOC is like using the range feature on your trip computer. It's not as accurate as the fuel gauge (which has its own accuracy issues) but using the miles to go as a guide to refueling will keep you from running out of gas.

Nothing wrong with monitors - they provide good knowledge of AH in and out (assuming a good calculation of charging losses and static discharge). The geek in me likes the monitor idea.

Fred W
2014 Rockwood A122 A-frame with dual 6V 232AH GC-2
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[Alben]

Update on a couple of long towing days.

I towed my trailer last week from MN to MO and back for 12 hours each way. The trip from MN to MO had temps from 88F to 95F for those 12 hours (excessive heat watch). The three way fridge was on 12VDC during travel. The fridge temp increased from 32F to 38F in those 12 hours. I monitored the trailer battery from within the tow vehicle. My tow vehicle was able to provide the entire demand current of the fridge. There was absolutely no drain from the trailer battery. We also stopped several times for rest stops and gas, which resulted in a 15% drain from the trailer battery. When resuming towing after the rest stops, the tow vehicle kept supplying the fridge current AND actually charged the trailer battery a couple percent points (not much).

[OYO]

Originally Posted by Alben

Update on a couple of long towing days.

I towed my trailer last week from MN to MO and back for 12 hours each way. The trip from MN to MO had temps from 88F to 95F for those 12 hours (excessive heat watch). The three way fridge was on 12VDC during travel. The fridge temp increased from 32F to 38F in those 12 hours. I monitored the trailer battery from within the tow vehicle. My tow vehicle was able to provide the entire demand current of the fridge. There was absolutely no drain from the trailer battery. We also stopped several times for rest stops and gas, which resulted in a 15% drain from the trailer battery. When resuming towing after the rest stops, the tow vehicle kept supplying the fridge current AND actually charged the trailer battery a couple percent points (not much).

Thanks for the update Alben. I get similar results, maybe a slight drain while underway. I think there is some corrosion on my trucks 7pin connector.

Maybe it's time for a new truck

[pgandw]

Originally Posted by Alben

Update on a couple of long towing days.

I towed my trailer last week from MN to MO and back for 12 hours each way. The trip from MN to MO had temps from 88F to 95F for those 12 hours (excessive heat watch). The three way fridge was on 12VDC during travel. The fridge temp increased from 32F to 38F in those 12 hours. I monitored the trailer battery from within the tow vehicle. My tow vehicle was able to provide the entire demand current of the fridge. There was absolutely no drain from the trailer battery. We also stopped several times for rest stops and gas, which resulted in a 15% drain from the trailer battery. When resuming towing after the rest stops, the tow vehicle kept supplying the fridge current AND actually charged the trailer battery a couple percent points (not much).

Thank you. Pretty much matches what I have seen regarding battery and towing with fridge on DC. Adding the computer case fan (tie-wrapped to the exhaust vent) helps keep the fridge temps steady.

When we are moving at 50+ MPH, the airflow is sufficient to keep fridge temps steady on even the hottest days without the fan. But as we stop or get in city traffic, the fridge temps climb unless the fan is on.

If it's a cool day - outside temps below 80, I leave the fan off. When driving, the fridge temp will pull down into the high 20s. When stopped or slow, the fridge warms up some with the fan off. This helps avoid freezing the food.

If we are dry camping, I try to get the fridge into the high 20s with about 2 hours to go on the road. I then turn the fridge off for the last 2 hours to let the TV make up the lost charge in the batteries. I arrive at site with full batteries and a fridge warmed up to high 30s. Put the fridge on gas and all is good.

The computer case fan draws 70ma, so battery use in negligible. But the difference in fridge performance is huge.

The thing that blows my plans out of the water is forgetting to latch the fridge door. The door pops open while towing, and all the cooling is lost. The remote thermometer has caught my mistake for me a couple of times.

Thanks again for your report.
Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time.