BMV-712 Battery Monitor Install Questions

[kayakist]

I'm tech challenged so requesting info on below questions before I hook anything up.


1. Motorhome batteries connected in parallel so:


a. Connect negative cable with accordion shielding to "Load and Charger" lug on shunt?


b. Buy another cable to connect from negative battery post to "Battery Only" lug on shunt? What size cable do I buy? 4 AWG or 2 AWG?



2. Connect positive red cable to shunt B1 for power. Since batteries in parallel no need to connect wire to B2?


Any suggestions on other things to be aware of?



I hope the batteries have identification on them somewhere so I can figure out battery capacity for system setup.



Thanks for your help.

[01tundra]

See below -

Originally Posted by kayakist

I'm tech challenged so requesting info on below questions before I hook anything up.


1. Motorhome batteries connected in parallel so:


a. Connect negative cable with accordion shielding to "Load and Charger" lug on shunt? YES


b. Buy another cable to connect from negative battery post to "Battery Only" lug on shunt? What size cable do I buy? 4 AWG or 2 AWG? Yes, match existing wire size.



2. Connect positive red cable to shunt B1 for power. Since batteries in parallel no need to connect wire to B2? If you're using the temperature sensor then red to B1 and black to B2. If no temp sensor and you want to monitor both batteries as one the just red to B1. If you want to monitor the batteries separate then there's an option of monitoring midpoint by connecting B2 to the negative of the 1st battery, but not sure why you'd really want to do that with just two 12V batteries in parallel. If one was a starter battery and one a house I could see monitoring each separately. If they are both house batteries I would monitor them as a single bank.

The FAQ's on the Victron site are very helpful to review for specific set ups


Any suggestions on other things to be aware of? After set up don't forget to remove the load side cable and calibrate the meter to zero under the battery settings option.



I hope the batteries have identification on them somewhere so I can figure out battery capacity for system setup.



Thanks for your help.

[kayakist]

Originally Posted by 01tundra

See below -

Thank you so much for taking the time to reply. I will install next week and will post status (or more questions if I hose something up).

[CHICKDOE]

Knowing which cable to disconnect from the battery is important. From your picture you want to disconnect the black cable connected to the negative terminal in the lower left. Ignore the black jumper cable that is connecting the two negative battery terminals. Just leave that jumper. Put the cable you disconnected on the load side of the shunt. Install the new cable you are going to buy on the battery side of the shunt and on the negative terminal that you removed the original cable from. This will ensure that all current that used to flow on the original cable now flies through the shunt.

You might want to see how much slack you have in the cable you are going to disconnect. This will help you determine where you can mount the shunt while still being able to connect the existing cable to it. Once you know where the shunt will be located you can measure to see how long of a new cable you will need to get from the shunt to the negative battery terminal.

[TitanMike]

01Tundra- mid point monitoring with a BMV712 is very useful wgen using 2 6v batteries in series.

After a few deep cycles cells can get out of balance. Lead acid batteries are cell balanced by just continuing charge until all cells are fully charged.

Problem arises when one battery is more "worn out" than the other. Mid point voltage monitoring can reveal the battery that doesn't fully charge as fast and warn of an issue that may harm both batteries.

Lithium batteries avoid this issue by utilizing a BMS that assures proper cell balancing without telyinh on overcharging some cells to get a full charge.

[Rolland]

I’m working on my install of the BMV712 and have planned to install the temp sensor. My question is can it be installed along with the wiring for Mid Point Monitoring, I have 2 6v GC2 batteries.

Originally Posted by TitanMike

01Tundra- mid point monitoring with a BMV712 is very useful wgen using 2 6v batteries in series.

After a few deep cycles cells can get out of balance. Lead acid batteries are cell balanced by just continuing charge until all cells are fully charged.

Problem arises when one battery is more "worn out" than the other. Mid point voltage monitoring can reveal the battery that doesn't fully charge as fast and warn of an issue that may harm both batteries.

Lithium batteries avoid this issue by utilizing a BMS that assures proper cell balancing without telyinh on overcharging some cells to get a full charge.

[01tundra]

Originally Posted by TitanMike

01Tundra- mid point monitoring with a BMV712 is very useful wgen using 2 6v batteries in series.

After a few deep cycles cells can get out of balance. Lead acid batteries are cell balanced by just continuing charge until all cells are fully charged.

Problem arises when one battery is more "worn out" than the other. Mid point voltage monitoring can reveal the battery that doesn't fully charge as fast and warn of an issue that may harm both batteries.

Lithium batteries avoid this issue by utilizing a BMS that assures proper cell balancing without telyinh on overcharging some cells to get a full charge.

Yes this is another option.

When I was running two 6V in series I did not monitor mid point and it all worked out fine for us for over three years. I just used a temperature sensor option.

There's no real right or wrong answer, it's purely personal preference.

[TitanMike]

Originally Posted by Rolland

I’m working on my install of the BMV712 and have planned to install the temp sensor. My question is can it be installed along with the wiring for Mid Point Monitoring, I have 2 6v GC2 batteries.

The monitor will only allow one or the other. Connection to shunt is for mid-point OR temp sensor. Monitor requires setup for either one used. Temp lead uses thermistor and for voltage you need a direct wire. Could be done but it would require a selector switch and constant changing of setup.

On FLA batteries, if also using a Victron solar controller, the temp is used to adjust charging voltages based on battery temp which can extend battery life/health.

[TitanMike]

Originally Posted by 01tundra

Yes this is another option.

When I was running two 6V in series I did not monitor mid point and it all worked out fine for us for over three years. I just used a temperature sensor option.

There's no real right or wrong answer, it's purely personal preference.

Mid point monitoring is most usefull if DEEP cycling series connected batteries. If following the 50% convention, th as t barely qualifies as Deep Cycling.

I agree, it's a matter of choice.

[Tom48]

Your question about being able to tell the amperage rating of your batteries is a good one. You do not really care about cold cranking amps or Marine cranking amps. And the minutes is kind of a meaningless number for our purposes. True Deep cycle batteries even the "Marine/starter batteries", which may not be the best deep cycle batteries, have an ampere trading. Deep cycle will always have an amp hour rating. That rating means how many amps you can draw at a limited rate., from full to dead. Draw at higher rate you won't get as much life. Draw it a lower rate you may get a little more life. Remember with what cell batteries as soon as they've been in use for any amount of time they will not likely hold their full capacity. It is what it is. Suggest you take the load off and charge those batteries at a slower moderate rate for at least 24 hours if not longer before you synchronize the full charge status of your shot system. That way you know you are as maxed as possible.

[TitanMike]

Originally Posted by Tom48

Your question about being able to tell the amperage rating of your batteries is a good one. You do not really care about cold cranking amps or Marine cranking amps. And the minutes is kind of a meaningless number for our purposes. True Deep cycle batteries even the "Marine/starter batteries", which may not be the best deep cycle batteries, have an ampere trading. Deep cycle will always have an amp hour rating. That rating means how many amps you can draw at a limited rate., from full to dead. Draw at higher rate you won't get as much life. Draw it a lower rate you may get a little more life. Remember with what cell batteries as soon as they've been in use for any amount of time they will not likely hold their full capacity. It is what it is. Suggest you take the load off and charge those batteries at a slower moderate rate for at least 24 hours if not longer before you synchronize the full charge status of your shot system. That way you know you are as maxed as possible.

Amp hour capacity can be ESTIMATED by dividing Reserve Capacity (RC) by 60 then multiplying by 25 ( the current used to determine RC).

Won't be perfect but a starting point. Results on BMV 712 can be adjusting ah capacity up or down over a few cycles until meter matches perfirmance more closely.

OR

One could attached a known load, measure time until battery is officially at 20% SOC and determine ah capacity more exact. Just recharge immediately to mitigate damage.

[kayakist]

Well... I took out one battery to see if any identification could be found with no luck. There is a bar code sticker on it that has D24DC-100 on it.


Assume that means Group 24 battery. Does the 100 signify 100 amps?



Expect to get the additional negative cable in the next couple of days to complete the install.


Thanks to all for the valuable information so far.

[Tom48]

Originally Posted by kayakist

Well... I took out one battery to see if any identification could be found with no luck. There is a bar code sticker on it that has D24DC-100 on it.


Assume that means Group 24 battery. Does the 100 signify 100 amps?



Expect to get the additional negative cable in the next couple of days to complete the install.


Thanks to all for the valuable information so far.

Well I'm pretty sure the 24 signifies that it's a group 24 size but I've never seen a group 24 battery with 100 amps so no idea what that means.

They range usually between 65 and 75 amps rating. I even had one once I think was only a 60 amp rating. That was a cheap battery that a dealer would have been proud to sell you.

[kayakist]

That's what I'm afraid of. Is there any way to determine the amps of the battery?


If not, I'm going to have to guess the battery bank capacity to enter into the monitor system.

Originally Posted by Tom48

Well I'm pretty sure the 24 signifies that it's a group 24 size but I've never seen a group 24 battery with 100 amps so no idea what that means.

They range usually between 65 and 75 amps rating. I even had one once I think was only a 60 amp rating. That was a cheap battery that a dealer would have been proud to sell you.

[Tom48]

Originally Posted by kayakist

That's what I'm afraid of. Is there any way to determine the amps of the battery?


If not, I'm going to have to guess the battery bank capacity to enter into the monitor system.

Since I think the basic purpose of the 712 is to measure the relative status of your batteries might determining how much is used and how much is put back in. So probably it would be safe just to assume each group 24 battery at 7:00 p.m. then set your parameters so you don't use more than half of that or at least Don't let it go below about 45% of the worst case scenario and you should be okay you will have a measurement of power in versus power consumed and if you zero the system out with your batteries fully fully fully fully fully charged then you're home free

[TitanMike]

Originally Posted by Tom48

Since I think the basic purpose of the 712 is to measure the relative status of your batteries might determining how much is used and how much is put back in. So probably it would be safe just to assume each group 24 battery at 7:00 p.m. then set your parameters so you don't use more than half of that or at least Don't let it go below about 45% of the worst case scenario and you should be okay you will have a measurement of power in versus power consumed and if you zero the system out with your batteries fully fully fully fully fully charged then you're home free

7:00 p. m. ?????? I'm assuming that might be a mis-type.


A quick search for group 24 Marine type Deep Cycle batteries seems to show most at 75 Amp Hour capacity..

I'd start with that and see how a 50% depth of discharge correlates with the normal 12.06 volt (resting for a couple hours) reading which is considered the 50% DOD Voltage reading.

If voltage is lower, lower setting for capacity and if voltage is higher, increase.

Since Ah rating on batteries is often advertised using a 20 hour rate, your "tailoring" the capacity in the above manner will match your useage which may equate to a lower hour rate. If your average discharge rate is only 10 amp your Ah rating will actually be higher.

Lead Acid batteries are electro-chemical devices and their capacities are highly dependent on the rate power is used. Just use the default Peukert factor and watch how SOC voltage matches up with SOC display on the Victron monitor. Adjust capacity as necessary until you replace batteries with a KNOWN capacity.

[01tundra]

Originally Posted by TitanMike

7:00 p. m. ?????? I'm assuming that might be a mis-type.


A quick search for group 24 Marine type Deep Cycle batteries seems to show most at 75 Amp Hour capacity..

I'd start with that and see how a 50% depth of discharge correlates with the normal 12.06 volt (resting for a couple hours) reading which is considered the 50% DOD Voltage reading.

If voltage is lower, lower setting for capacity and if voltage is higher, increase.

Since Ah rating on batteries is often advertised using a 20 hour rate, your "tailoring" the capacity in the above manner will match your useage which may equate to a lower hour rate. If your average discharge rate is only 10 amp your Ah rating will actually be higher.

Lead Acid batteries are electro-chemical devices and their capacities are highly dependent on the rate power is used. Just use the default Peukert factor and watch how SOC voltage matches up with SOC display on the Victron monitor. Adjust capacity as necessary until you replace batteries with a KNOWN capacity.

Yep ^.

And the "resting for a few hours" is very important to remember for accuracy purposes.

[kayakist]

Thanks for this, makes sense.


I'm taking a trip next week and will make the final system connections then and report back.

Originally Posted by TitanMike

7:00 p. m. ?????? I'm assuming that might be a mis-type.


A quick search for group 24 Marine type Deep Cycle batteries seems to show most at 75 Amp Hour capacity..

I'd start with that and see how a 50% depth of discharge correlates with the normal 12.06 volt (resting for a couple hours) reading which is considered the 50% DOD Voltage reading.

If voltage is lower, lower setting for capacity and if voltage is higher, increase.

Since Ah rating on batteries is often advertised using a 20 hour rate, your "tailoring" the capacity in the above manner will match your useage which may equate to a lower hour rate. If your average discharge rate is only 10 amp your Ah rating will actually be higher.

Lead Acid batteries are electro-chemical devices and their capacities are highly dependent on the rate power is used. Just use the default Peukert factor and watch how SOC voltage matches up with SOC display on the Victron monitor. Adjust capacity as necessary until you replace batteries with a KNOWN capacity.

[kayakist]

Sorry it took so long to post my progress. Thanks to the input from all of you the install went well.


I'm currently dry camping for the next five days so I'll be relying on the monitor heavily.


First use notice my 12V Everchill refrigerator draws about 6 amps. When I put the generator on it returns a little less than 4 amps. It will be interesting in the morning to see what I end up with.


For some reason the BMV shows .15 volts higher than a voltmeter directly on the terminals. Not sure why that is.


Wish the BMV phone app didn't refresh the trends tab everytime I log back in.


Anyway, enjoying the story so far.


Happy travels.