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Old 09-18-2022, 08:40 AM   #1
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Possible Victron BMV 712 issue

Hello,
Over last winter I had two 100Ah Battleborns installed in our Georgetown 34M5 along with the Victron BMV-712. I recently had the MH just run off the batteries in storage, with a fan on low, and when we next checked on it, there was nothing on in the coach(no power), and the batteries read 89.5 on the BMV-712.



I know I was trying to get the alarm to sound when below 20% SOC, then when above 25% to stop. Somehow I wondered if I messed up some settings, so I tried to turn most of the alarm settings off, but think I mixed up that with the 'relay' settings on the BMV-712.


This time when running solely on batteries with a fan running on low, when we returned to the coach, all power was off, and the BMV-712 read 88.4% for the batteries. Does this sound like anything obvious I messed up in the settings? Appreciate any help, was thinking to reset the BMV-712 back to it's default settings, but wanted to reserve that to a last resort.



Thanks,
Steve
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Old 09-18-2022, 12:04 PM   #2
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Some thoughts:

If you have altered the default configurations it is possible there might be an issue there. Some parameters are dependent on others to provide the desired results. One example is with the alarm settings and how that can affect SOC percentage display.

I would also make sure the shunt is installed correctly and ALL current entering or leaving the battery has to pass through it. Easiest way to be sure is to only have one wire attached to the battery negative terminal, going directly to the shunt's "battery terminal", and no other wires attached to that terminal on the shunt.

If all that was running was the fan, it may have been drawing power that bypassed the shunt.

I would check wiring to be sure and then return BMV-712 settings to default. Also perform a "zero current calibration" by disconnecting the negative wire(s) from the LOAD side of the shunt and follow instructions on app setup screen.

The shunt needs to remain connected to the battery negative terminal during this process so the shunt itself remains powered up.
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Old 09-18-2022, 12:51 PM   #3
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When was the last time you charged your batteries up to 100% and synchronized the meter at 100%?
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Old 09-18-2022, 07:51 PM   #4
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Thank you for the reply, TitanMike! I will check on all that tomorrow when I can see better. As an update, we got to our campground, and have been plugged in and charging the batteries for about 5-6 hrs. The monitor has gone from the 88.4% to currently 99.5% SOC, is it possible the 88.4 was a bogus reading(actually batteries being dead), and the now reading of 99.5% is actually accurate without me changing any settings. I take that back, I did change and turn on a setting called Invert Relay which gave a clicking sound, could that be the issue?


I do have 2 settings called "Synchronize SOC to 100%, and "Zero current Calibration" I have never used, as I thought when the charge reaches 100% it is automatically calibrated. Would either of those help, when I hit 100% tonight?
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Old 09-18-2022, 07:57 PM   #5
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When was the last time you charged your batteries up to 100% and synchronized the meter at 100%?



Thanks eric1514! See my above reply to TitanMike for some more info, I have not ever done the synchronization at 100% I guess I'm confused, since I believe I ran the batteries down both times recently, while the BMV showed 89.5% one time and 88.4% the other, with a voltage of I think it was like 10.8 or close to that, how can I trust the reading of 100% when it finishes charging soon will be somewhat accurate, the current voltage does show 13.4V.
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Old 09-18-2022, 08:29 PM   #6
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Thank you for the reply, TitanMike! I will check on all that tomorrow when I can see better. As an update, we got to our campground, and have been plugged in and charging the batteries for about 5-6 hrs. The monitor has gone from the 88.4% to currently 99.5% SOC, is it possible the 88.4 was a bogus reading(actually batteries being dead), and the now reading of 99.5% is actually accurate without me changing any settings. I take that back, I did change and turn on a setting called Invert Relay which gave a clicking sound, could that be the issue?


I do have 2 settings called "Synchronize SOC to 100%, and "Zero current Calibration" I have never used, as I thought when the charge reaches 100% it is automatically calibrated. Would either of those help, when I hit 100% tonight?
The "invert relay" setting wouldn't cause this issue. It merely changes relay from normally open to normally closed (or vice-versa). Unless you are using the relay to switch something it's just there doing nothing.


Synchronizing 100% SOC should be automatic and will be affected by the tail current setting. After your charging current drops to near nothing it might not hurt to hit the "synchonize 100%" "button".

I would definitely perform the zero current calibration if you've never done it. Just make sure to disconnect negative connectionvto the shunt as I described. If not you'll program in a current offset which means that although the monitor reads zero amps, there is still some current flowing.
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Old 09-19-2022, 03:03 PM   #7
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Check setting 07 on page 22 of the manual. This is "Current Threshold". Currents below this setting are disregarded by the BMV-712 and so do not register and are not factored into the SOC reading. I.e., if this setting is 0.2 amps and you have a fan drawing 0.15 amps, that current will be ignored by the BMV-712. The default is 0.1 amps.

Even if you use the default setting of 0.1 amps, your parasitic loads such as propane sensor may total less than 0.1 amps and run the battery down without the BMV-712 readings changing.

Whether or not this is the problem, it's good to know this setting and keep it in mind since it can lead to a higher than actual SOC reading given that some Ah use is being ignored by the BMV-712.

There are also some lithium-specific settings listed in chapter 6 that are very important. You've probably taken care of these, but they are worth checking because not using the lithium specific settings can result in higher than actual SOC readings.

As others have mentioned, be sure the BMV-712 shut is installed so that it sees ALL loads and charging that occur.

Resetting the BMV-712 and starting over on the lithium-specific settings isn't a bad idea as there are so many settings that might have accidentally been changed, it's very tedious and difficult to check all of them.
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Old 09-19-2022, 03:56 PM   #8
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The "invert relay" setting wouldn't cause this issue. It merely changes relay from normally open to normally closed (or vice-versa). Unless you are using the relay to switch something it's just there doing nothing.


Synchronizing 100% SOC should be automatic and will be affected by the tail current setting. After your charging current drops to near nothing it might not hurt to hit the "synchonize 100%" "button".

I would definitely perform the zero current calibration if you've never done it. Just make sure to disconnect negative connectionvto the shunt as I described. If not you'll program in a current offset which means that although the monitor reads zero amps, there is still some current flowing.

I did perform the "synchronize to 100%" last night after the charging stopped and the BMV showed 99% so by hitting that button, of course, it went to 100%. Since it seemed to charge for 5 or so hours, I'm wondering if it is ok now, even though it took that long to go from 88.4%( which was fully drained as nothing would run, couldn't start the generator, etc...) to the 99%.



It looks like everything on the negative side runs through the shunt, so for now I'm thinking I run another test when we get back home and see if things are ok.
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Old 09-19-2022, 04:07 PM   #9
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Originally Posted by Hclarkx View Post
Check setting 07 on page 22 of the manual. This is "Current Threshold". Currents below this setting are disregarded by the BMV-712 and so do not register and are not factored into the SOC reading. I.e., if this setting is 0.2 amps and you have a fan drawing 0.15 amps, that current will be ignored by the BMV-712. The default is 0.1 amps.

Even if you use the default setting of 0.1 amps, your parasitic loads such as propane sensor may total less than 0.1 amps and run the battery down without the BMV-712 readings changing.

Whether or not this is the problem, it's good to know this setting and keep it in mind since it can lead to a higher than actual SOC reading given that some Ah use is being ignored by the BMV-712.

There are also some lithium-specific settings listed in chapter 6 that are very important. You've probably taken care of these, but they are worth checking because not using the lithium specific settings can result in higher than actual SOC readings.

As others have mentioned, be sure the BMV-712 shut is installed so that it sees ALL loads and charging that occur.

Resetting the BMV-712 and starting over on the lithium-specific settings isn't a bad idea as there are so many settings that might have accidentally been changed, it's very tedious and difficult to check all of them.

The Current threshold I left at the default of 0.1 amps, and with the fan running on low I know that is above that, not counting any other continous drains, and everything else in Chapter 6 seems good.
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Old 09-19-2022, 05:01 PM   #10
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The Current threshold I left at the default of 0.1 amps, and with the fan running on low I know that is above that, not counting any other continous drains, and everything else in Chapter 6 seems good.
Running out of wild guesses ....... but not giving up.

Had the batteries seen 100% SOC at some point in time before the two winter storage events?

How long did the RV sit with just the fan and parasitic loads running during the two events that got the indicated SOC down into an the 80's? (with actual SOC much lower)

What was the current load on the battery with the fan and parasitic devices on it?

Did the event hours times this (next above) load current total up around 200 Amperehours?

Was the ~5 hour re-charge current about 40 amps? (indicating 200 Ah of charge from depleted to full)
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Old 09-19-2022, 09:07 PM   #11
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Running out of wild guesses ....... but not giving up.

Had the batteries seen 100% SOC at some point in time before the two winter storage events?

How long did the RV sit with just the fan and parasitic loads running during the two events that got the indicated SOC down into an the 80's? (with actual SOC much lower)

What was the current load on the battery with the fan and parasitic devices on it?

Did the event hours times this (next above) load current total up around 200 Amperehours?

Was the ~5 hour re-charge current about 40 amps? (indicating 200 Ah of charge from depleted to full)

Appreciate all the help, the 2 events were both recent, the most recent one was only after 24 hours, the battery monitor went from 99.5% to 96.5% in 24 hours, I was just trying to see what the usage would be with a ceiling mounted fan on low. Realizing it seemed like only 3% used, I then came back 3 days later for our current local trip in the MH, and all power was off, reading was 88.4% SOC, voltage was like upper 10's or lower 11's and nothing came on. I had to pull from chassis battery to start the generator. Figured since trip was 30 minutes away, the generator could start charging the batteries, and we needed to run it as we do monthly.


The batteries were at 100% SOC a week prior to this most recent event.



I didn't really think to look at the re-charge current, guess I kinda assumed all was fine, and now realize if I would have, that would have contributed more valuable information
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Old 09-20-2022, 01:52 AM   #12
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Appreciate all the help, the 2 events were both recent, the most recent one was only after 24 hours, the battery monitor went from 99.5% to 96.5% in 24 hours, I was just trying to see what the usage would be with a ceiling mounted fan on low. Realizing it seemed like only 3% used, I then came back 3 days later for our current local trip in the MH, and all power was off, reading was 88.4% SOC, voltage was like upper 10's or lower 11's and nothing came on. I had to pull from chassis battery to start the generator. Figured since trip was 30 minutes away, the generator could start charging the batteries, and we needed to run it as we do monthly.


The batteries were at 100% SOC a week prior to this most recent event.



I didn't really think to look at the re-charge current, guess I kinda assumed all was fine, and now realize if I would have, that would have contributed more valuable information
3% over 24 hours is 6 Ah or about 1/4 amp. That's about right for a fan on low (at least it would be for my MaxxFans). Losing another 8 Ah over the next three days is, again, about 1/4 amp. So the SOC percent numbers make sense.

Did you notice the Ah reading associated with those SOC percentages?

These aren't by any chance heated batteries? The heater would be internal and any current it draws would not be seen by the BMV-712. Clearly it's not the season for the battery heater to come on automatically. If there are heaters, did they by any chance get turned on in some way?
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Old 09-20-2022, 04:55 AM   #13
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Old 09-20-2022, 07:01 AM   #14
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These aren't by any chance heated batteries? The heater would be internal and any current it draws would not be seen by the BMV-712. Clearly it's not the season for the battery heater to come on automatically. If there are heaters, did they by any chance get turned on in some way?

BINGO !! Great detective work Hclarkx! Yes indeed they are heated batteries, and I had a switch installed, unfortunately they installed it on the steps, where it could and did get flipped on With 2 dogs, guests, and my wife and I going continuously up and down the steps on our trips, I guess it was just a matter of time.



Now the question is how do I get it back to a true reading of 100%, and, of course, I'll need to place a cover to prevent accidentally turning this on.
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Old 09-20-2022, 07:12 AM   #15
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I thought that was something that needed to be switched on, but I may be wrong.
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Old 09-20-2022, 01:02 PM   #16
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Now the question is how do I get it back to a true reading of 100%, and, of course, I'll need to place a cover to prevent accidentally turning this on.
Should be as simple as charging current drops to near zero and then go into battery settings to synchonize to 100%.

Make sure that Charged voltage, Tail current, and Charge detection time are correctly set for your battery bank. Using defaults is probably best.

FWIW, here is what Battleborn suggests for the BMV-712 settings when using their batteries.

Quote:
For our batteries, use the following settings to program the BMV-712 Smart Battery Monitor:

Battery Capacity: Total Ah of your bank of batteries
Charged voltage: 14.4V but note that this number should be about .1 or .2 volts below the charging voltage set in your charging device
Discharge Floor: 0%
Tail Current: 2-4% is good
Charged Detection Time: 3m
Peukert Exponent: 1.05
Charge Efficiency Factor: 99%
Current threshold: 0.10A
Time to go averaging period 3m
Battery Starts Synchronized: blue button should be to the right
State of Charge: leave alone
Synchronize SOC to 100%: Leave alone, this device will sync itself at the top of the charge
Zero Current Calibration: Leave alone
BB does sugest the "Battery Starts Synchronized" button be ON. Only time this would cause an issue is if the batteries are totally disconnected and the BMV-712 goes dead. When powered back up it will reset to 100% SOC regardless of the actual battery SOC. Cure is as simple as just leaving charger connected long enough that one KNOWS the batteries are at 100% SOC and then synchornize manually.
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Old 09-20-2022, 01:50 PM   #17
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That synchronize to 100% switch is described in item 70 on page 30 of the manual. The description is a bit vague but It seems that the BMV-712 forgets the SOC if it is disconnected and this switch gives you the choice between 100% and some unknown reading when the BMV is put back into service. It's best to leave the BMV always connected and on and be sure the LiFePO4 batteries get topped off at least once every week or two when in daily use to "synchronize" the SOC reading.

Ideally, the SOC reading would not change when you disconnect the BMV for some service work and then reconnect it (since the SOC is not likely to change during that time). I don't know that the BMV does this or where the "unknown" SOC reading comes from. Best to just let the top-off process update the SOC reading.

If the battery is not topped off for a while, the SOC reading will drift up relative to the actual SOC. When this happens, the indicated SOC will hit 100% before the battery is topped off and sit at 100% during the remainder of the charge time. Do not stop charging when the SOC indicates 100%. Continue charging until the voltage hits at least 14.2 Volts or a bit higher (most chargers will go to 14.4V). After a full charge the SOC will read 100% and start counting down as you discharge (use) the battery. This is automatic. You do not need to take any action and do not need to change the "100%" switch position.

The SOC reading can be made more accurate by setting the Peukert's exponent for your usage. The manual recommends 1.05. 1.05 is best for those frequently running a microwave or other large loads from the battery. With more typical small loads (propane heater motor and lights) a setting of 1.02 is more likely to keep the SOC tracking actual charge state well.

But, to your question. You can use the 100% switch to set the BMV to 100% if you know the battery is actually at or near 100%. Otherwise this switch is pretty useless. Personally, I would leave it off and depend on charging the battery up to 100% to re-synchronize the SOC reading.

As for the detective work, thanks for the kudo. A good part of my career was spent doing forensics on electric power grid blackouts. So this was a natural for me.
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Old 09-20-2022, 02:39 PM   #18
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Should be as simple as charging current drops to near zero and then go into battery settings to synchonize to 100%.

Make sure that Charged voltage, Tail current, and Charge detection time are correctly set for your battery bank. Using defaults is probably best.

FWIW, here is what Battleborn suggests for the BMV-712 settings when using their batteries.


BB does sugest the "Battery Starts Synchronized" button be ON. Only time this would cause an issue is if the batteries are totally disconnected and the BMV-712 goes dead. When powered back up it will reset to 100% SOC regardless of the actual battery SOC. Cure is as simple as just leaving charger connected long enough that one KNOWS the batteries are at 100% SOC and then synchornize manually.

Great, that's a good double-check, I did originally set per Battleborn's recommendations, and have checked a couple times and all is still set correctly. The tail current I set to 4 which was withing their given range of 2-4.
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Old 09-20-2022, 04:16 PM   #19
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Great, that's a good double-check, I did originally set per Battleborn's recommendations, and have checked a couple times and all is still set correctly. The tail current I set to 4 which was withing their given range of 2-4.
4 is fine. I'd set it even higher since the added charge in that stage is negligible and isn't worth the life it takes out of the battery (IMHO).

I set my charging to go to 14.4 and then switch to float. Enabling the second mode that holds voltage until tail current drops is a hold-over from lead acid days. It does increase the charge level but only factionally (less than a percent). IMHO the LiFePO4 wear and tear of that charge stage LiFePO4 is not worth the fraction of a percent charge it adds. But, I'm splitting hairs. I'm probably adding only a year to the life of my LiFePO4 by not going fully to 100% (getting maybe 16 years instead of 15.5 years out of it). I only charge with solar controllers which allow me to skip the "tail current" stage.
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Old 09-20-2022, 04:31 PM   #20
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That synchronize to 100% switch is described in item 70 on page 30 of the manual. The description is a bit vague but It seems that the BMV-712 forgets the SOC if it is disconnected and this switch gives you the choice between 100% and some unknown reading when the BMV is put back into service. It's best to leave the BMV always connected and on and be sure the LiFePO4 batteries get topped off at least once every week or two when in daily use to "synchronize" the SOC reading.

I leave the BMV connected in storage, and plugged into 120V power most of the time, I just decided to test the batteries only and left it unplugged, and with the fan on low and whatever else runs(seat lighting, LED clocks, etc...) it only used approx 3% each night. At each campsite I am plugged into 50Amp power.


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Originally Posted by Hclarkx View Post
Ideally, the SOC reading would not change when you disconnect the BMV for some service work and then reconnect it (since the SOC is not likely to change during that time). I don't know that the BMV does this or where the "unknown" SOC reading comes from. Best to just let the top-off process update the SOC reading.

Makes sense, even to my limited knowledge


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If the battery is not topped off for a while, the SOC reading will drift up relative to the actual SOC. When this happens, the indicated SOC will hit 100% before the battery is topped off and sit at 100% during the remainder of the charge time. Do not stop charging when the SOC indicates 100%. Continue charging until the voltage hits at least 14.2 Volts or a bit higher (most chargers will go to 14.4V). After a full charge the SOC will read 100% and start counting down as you discharge (use) the battery. This is automatic. You do not need to take any action and do not need to change the "100%" switch position.

When camping or hooked to 120V power(in storage), I am always plugged in, except the past week to do a test, so only occasionally do I leave the MH unplugged in storage. I know on this trip the BMV read 88.4% charged, but batteries seemed dead, Once I arrived Sunday afternoon, I left it on 50Amp and has been so for the last 2 days. About 5 hrs. after getting here Sunday night, it read 99% and had stopped charging at 99%, with batteries hovering around 13.5V. It wasn't until about 18 hrs. later when I turned off the battery heaters, so not sure if I am sitting at 99% charge minus 17 hrs. of the heaters being on, or less than that. Hope this makes sense, and since I am not able to give the figures during charging, I know this is hard for you to troubleshoot.


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The SOC reading can be made more accurate by setting the Peukert's exponent for your usage. The manual recommends 1.05. 1.05 is best for those frequently running a microwave or other large loads from the battery. With more typical small loads (propane heater motor and lights) a setting of 1.02 is more likely to keep the SOC tracking actual charge state well.

I have Peukert's set to 1.05, we use the microwave fairly often.


Quote:
Originally Posted by Hclarkx View Post
But, to your question. You can use the 100% switch to set the BMV to 100% if you know the battery is actually at or near 100%. Otherwise this switch is pretty useless. Personally, I would leave it off and depend on charging the battery up to 100% to re-synchronize the SOC reading.
Quote:
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As for the detective work, thanks for the kudo. A good part of my career was spent doing forensics on electric power grid blackouts. So this was a natural for me.

Well, that definitely explains your knowledge, and definitely appreciate your willingness to share and help out. I may need you to dummy it down, sorry to ask the same question, but since my batteries (2 x 100Ah) showed 99% after charging for approx. 5 hrs, and are currently sitting at 13.53V, and the battery heaters appear to be off now and out of the equation, does this appear that they are basically fully charged, is that how I can tell?
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