BMV 702 Setup

[PaulF007]

I finally got around installing the midpoint voltage connector but it does not look like the BMV 702 is reading it as mid point voltage rather as n Aux voltage. Is there a setting that I must apply to get the midpoint to monitor?

Best regards

Paul 

[Guest]

When you selected midpoint. Did you save it.

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[PaulF007]

Hi Manie nope - as a matter of fact I didn't select midpoint only connected the terminal to the BWV the rest is still stock standard from the box, except for the battery setting that is.

[Guest]

Just go through the settings and select midpoint and save it. I am currently at work. But will gladly help you if you cant set it up

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[Jaco De Jongh]

Hi Paul. You must select the function of the aux input. It is setting 69. Just select "Mid"

[PaulF007]

Thank you Manie, I noticed in the manual that when setup the BMV for the first time you need to select the function but how do you get to that setting after your first setup is done? 

[Jaco De Jongh]

Paul , Press and hold SETUP for more than 2 seconds. Scroll down to desired parameter and then you can change it.

[Guest]

Jaco explaine very well. If i remember correctly. I reseted the bmv and then selected it

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[PaulF007]

Hi Jaco, Ah now I see it on the manual as well , man I must have gone through it almost 5 time and didn't see it. 

Thank you! I will look at it tomorrow morning , almost on my way to the Bok game this afternoon  

[Jaco De Jongh]

@PaulF007 I have done the same, thought its a quick setup, just did what I thought was needed, and then when wanted to add Mid, I had the same problem, I could not find it at first.

Enjoy the game

[PaulF007]

That will be up to the boks if I enjoy it  , but will enjoy the outing!!!

[Jaco De Jongh]

Hi Paul, I want to hi-jack this thread , Don't want to start a new thread on 702 Questions.

1. What is the best way to determine tail current for a 450Ah bank
2. Does the type of battery play a role in calculating tail current
3. How often do you guys manually sync your 700/702's.
4. Do you feel a manual sync is necessary, and if so, how often would you recommend it.

[Guest]

Adding question 5 to Jaco's question.

5. Has anyone noticed that their BMV is giving a battery voltage of X, yet if you measure the actual batteries, the voltage is lower like by +-0.5 volts?

[Chris Hobson]

30 minutes ago, Jaco de Jongh said:

Hi Paul, I want to hi-jack this thread , Don't want to start a new thread on 702 Questions.

1. What is the best way to determine tail current for a 450Ah bank
2. Does the type of battery play a role in calculating tail current
3. How often do you guys manually sync your 700/702's.
4. Do you feel a manual sync is necessary, and if so, how often would you recommend it.

Hi Jaco

1. Tail current is a matter of trial and error. The 4% default is a bit high.  I steadily reduced it and my current setting is 2.8% with a charged detection time of 30 minutes. It is still not 100% witht the Axpert showing fully charged marginally before the BMV shows 100% but I am happy with the setting.
2. No not that I know of.
3. Never - with the Axpert showing fully charged marginally before the BMV I am happy for it to sync about 5 minutes later.
4. Only if you spent time fiddling and disconnecting. Once your BMV has been connected for a day or two you can forget about it except obviously looking at the readings.

   32 minutes ago, The Terrible Triplett said:

   Adding question 5 to Jaco's question.

   5. Has anyone noticed that their BMV is giving a battery voltage of X, yet if you measure the actual batteries, the voltage is lower like by +-0.5 volts?

    
5. BMV and Axpert agree. If there is any discrepancy it is within 0.05V. This  can probably be attributed to momentarily delay between recording and logging of data of the two devices.

[Guest]

2 minutes ago, Chris Hobson said:

5. BMV and Axpert agree.

Yes, it should agree. Can live with 0.05v, but 0.5v on 24v or 12v system is quite a bit.

My BMV 600 disagrees with my volt meter and new small inverters. Both of them reads the same volts yet BMV reads 0.5v more.

Resulting in BMV being happy at 98% SOC with 24.6v under load, yet inverter is warning me of low volts of 24.1v.

 

[viper_za]

39 minutes ago, The Terrible Triplett said:

Yes, it should agree. Can live with 0.05v, but 0.5v on 24v or 12v system is quite a bit.

My BMV 600 disagrees with my volt meter and new small inverters. Both of them reads the same volts yet BMV reads 0.5v more.

Resulting in BMV being happy at 98% SOC with 24.6v under load, yet inverter is warning me of low volts of 24.1v.

 

Do you have it configured for the correct shunt?

[Guest]

3 minutes ago, viper_za said:

Do you have it configured for the correct shunt?

Mmmm ... good pointer. Yes, I believe so. It is the one it came out with.

I also have a BMV700 and the shunts look identical, are supposed to be identical?

[viper_za]

23 minutes ago, The Terrible Triplett said:

Mmmm ... good pointer. Yes, I believe so. It is the one it came out with.

I also have a BMV700 and the shunts look identical, are supposed to be identical?

Just make sure on the BMV
Shunt current
Shunt voltage

If they are how much do you trust your multimeter

[Guest]

42 minutes ago, viper_za said:

If they are how much do you trust your multimeter

Well, on the other system, BMV says 25.66volts, inverter says 25.56v and Multimeter on batteries says 25.66v, I recon I will take a leap of faith and say that I can trust the multimeter to read at least the volts right.

What do you think? 

 

 

[___]

Cheapie multimeters are pretty terrible. Basically anything under R1000 should be carefully tested against something you know to be accurate before making assumptions. My Uni-T meter was about R500 and is remarkably good for the price, but still only a 2000-step meter and often off by as much as 0.02V. I can live with that though. If I need that level of accuracy, I use the scope.

One day when I'm all grown up, I'll get me a proper Fluke.

[Jaco De Jongh]

Thanks Chris

I will try that settings, I never really bothered as my batteries had enough time to charge, Just had 4 to 5  cloudy to partially cloudy days in a row, and for the first time after installing the 702 I doubted the readings, It was showing 100% with the battery volts sitting at 51.7Volts. 

I guess it was a case of charging and using the whole time without it really reaching 100%. that triggered the questions above. Time to fine tune that part of the BMV.

Thanks for adding TTT.

[viper_za]

42 minutes ago, The Terrible Triplett said:

Well, on the other system, BMV says 25.66volts, inverter says 25.56v and Multimeter on batteries says 25.66v, I recon I will take a leap of faith and say that I can trust the multimeter to read at least the volts right.

What do you think? 

 

 

Next question how far is that shunt from the batt then

[Guest]

Shunt is about 30cm from batts connected using a 25mm2 wire.

[superdiy]

1 hour ago, plonkster said:

Cheapie multimeters are pretty terrible. Basically anything under R1000 should be carefully tested against something you know to be accurate before making assumptions. My Uni-T meter was about R500 and is remarkably good for the price, but still only a 2000-step meter and often off by as much as 0.02V. I can live with that though. If I need that level of accuracy, I use the scope.

One day when I'm all grown up, I'll get me a proper Fluke.

My Fluke and BMV are within 0.01V of each other and I calibrated my inverter to as close as possible to that.  I've not hooked up my DS scope yet, basically bought it about 4 years ago and only used it once since - it is permanently stored in the vault.    But multimeters, inverters as well as oscilloscopes need to be calibrated and not only once, but at certain intervals, sometimes more than once a year depending on the level of accuracy you need.

1 hour ago, The Terrible Triplett said:

Shunt is about 30cm from batts connected using a 25mm2 wire.

Best way to test voltage is without any current flowing or with as little as possible, because depending on the resistance in the circuit and the amount of current flowing, you will get voltage drops - batteries must definitely not be charging or discharging while you do your measurements - on 25mm² cables the current drawn by the BMV should not make that much of a difference, but even then, try to measure where the BMV measures or as close as possible to those points - that would be on the battery side of the shunt (for negative) and the point where the lead from the battery positive enters the shunt PC board (positive).

[Guest]

@superdiy I will do that tonight again. Last night the inverter was on powering the lights, kept on warning me, that is why I checked.

Measured the volts on the batts themselves.
Then I measured at the inverter, on the cables, which is then other side of the shunt. Both readings where the same.

Yet the BMV was showing 0.50v more, which is messing up the SOC reading totally.