Victron 100/30 voltage measurement

[Paul L]

Originally Posted by noelex 77

0.03v is not of much significance, but if it is a consistent error it only takes a few seconds to adjust the Victron set points to cancel out the discrepancy. If there is some error due to voltage drop it will be a variable number, but you can still adjust the result so that under typical conditions the set points are as accurate as possible.

The loss of temperature compensation is more significant. There are two options without any additional Victron equipment.

1. Enable automatic temperature compensation. The temperature will be measured at the solar controller just before it turns on at the start of the day.
2. Disable automatic temperature compensation. Measure the temperature of the batteries and apply the compensation manually.

Personally I prefer 2. It helps to have remote display of the battery temperature although the adjustment is usually only done with a change of season, or significant change in location.

I can't see how #1 is much of any advantage. For my 12v AGMs absorption voltage varies nearly .3 v over 68*f(20c) to 86*f(30c). This can easily happen between early morning and full charge time.

[Yellowjacket]

Noelex,
Victron says their base line is 25ºC
Victron MPPT says temperature compensation coefficient is -16.20 mV.
Vict Battery Sense says my battery actual temp is 13ºC
Diff in actual temp from baseline is -12ºC
-12 x -16.20 x .001 = .1944
Victon absorption voltage at 25ºC is 14.40
At my battery temp, my absorption voltage should be ~14.6.
Do I understand this?

[Cowpoos]

Originally Posted by Jim Cate

I've recently upgraded my solar system with a couple of 42 V 200 W panels in parallel, plus a Victron 100/30 MPPT controller. It is all working quite well, and putting in some useful power.

I'm using their Bluetooth app to monitor the system... a neat and handy tool. However, I've noted that the battery voltage that is posted there is around 0.2 volts higher than that measured with a good DVM. This is measured right at the output terminals of the controller, so voltage drop is not the issue. The differential remains fairly constant over a wide range of output currents.

This, of course, means that the set Absorption, Float and Equalize voltage points are incorrect. I'm charging 4x T105s and have used the user defined protocol to set Absorption at 14.8, etc. So, when the reg thinks it is outputting the 14.8 volts, the batteries are only getting around 14.6. I have set the voltage higher to compensate for this, but don't really like that as a work around.

So, has anyone else seen a similar issue? And, is there a way to calibrate the voltmeter in the regulator? If no one here on CF has wisdom to offer, I'll try going to Victron directly, but am not optimistic that I will be able to reach a real competent human being.

Ideas?

Jim

Those chargers have automatic temperature compensation. The charge voltage alters at higher than average and higher than lower.
I think you can turn that feature off in the app to check and see if this is what is at play.

[Cowpoos]

Originally Posted by Cowpoos

Those chargers have automatic temperature compensation. The charge voltage alters at higher than average and higher than lower.
I think you can turn that feature off in the app to check and see if this is what is at play.

Hmmm, I only read two pages in and I can now see others have come to the same conclusion.

[Yellowjacket]

And, I'm increasing absorptions and equalization voltages another .04 V to make up for voltage drop: three voltage meters hooked to battery read 12.74 when MPPT hooked to bus bar in engine room reads 12.70.

Absorption goes to 14.64, float to 13.84.

Now I need to go to a different thread to find out why my Mastervolt Inverter Charger tells me the battery voltage is 1.2 volts higher when charging than meters on my battery. This definitely affects charging, and would explain why my Balmar chargers on engine and gen set are able to get battery to a higher SOC than the Mastervolt on shorepower.

[noelex 77]

Originally Posted by Erik Dolson

Noelex,
Victron says their base line is 25ºC
Victron MPPT says temperature compensation coefficient is -16.20 mV.
Vict Battery Sense says my battery actual temp is 13ºC
Diff in actual temp from baseline is -12ºC
-12 x -16.20 x .001 = .1944
Victon absorption voltage at 25ºC is 14.40
At my battery temp, my absorption voltage should be ~14.6.
Do I understand this?

Yes that is correct.

The only modification I would suggest is using the battery manufacturers temperature coefficient rather than the default value programmed into the controller. This correction should be applied to battery manufacturers set points for absorption and float to calculate the correct voltage.

For example the popular Trojan flooded batteries have a suggested temperature coefficient (from memory, so check if you are using these batteries) of 30mV per degree C which nearly doubles the voltage adjustment of the default 16.20mV applied by the controller (and this adjustment would be applied to the recomended 14.7v absortion voltage).

These examples show why using simple defaults, ignoring temperature compensation and errors in voltage measurment can sometime result in charging set points that are significantly wrong, resulting in extended charging times and a short battery life.

[Yellowjacket]

You have increased my understanding significantly and that is greatly appreciated. Thank you.

[daveNZ]

Can the ‘minimum voltage’ of the battery, as reported by the Victron MPPT, be taken as the lowest battery voltage, under load, as a guide to how discharged your house bank was overnight. e.g. I know battery voltage climbs about .3V from my biggest load (fridge) so if I see 11.9V as the battery minimum, then I’m happy to say that’s about 12.2V resting voltage and therefore about 50% SOC. (I also have a Victron BVM but without doing a C20 test I’m guessing at the current capacity. I’m also not a full time cruiser so things and $ are not as critical for me.)

[Yellowjacket]

I've been through my SBS battery manual. Argh. First, they make no adjustment to charging voltage if battery temp is between 50ºF and 86ºF. This does not seem right nor comply with discussion here from very knowlegable people.

Second, they do not mention absorption voltage at all. Only bulk, float and equalization. I include verbiage below.

My temptation is to use the SBS (Trojan, I think) voltage points (14.4 for bulk / absorption, 13.38 for float) and the Victron temperature correction factor. I have no clue as to why this appeals to me. Probably because it involves more possibly needless effort. Apparently, I'm big on that.

After confirming limitations of BatterySense, I had a nice conversation with Victron today. I suggested they might include in their sales info on the BatterySense that while it will broadcast to phone or Victron MPPT while holding same and sitting cross-legged just above the battery with sense mounted, signal is lost when one stands up or moves any further than height of person standing if he is not too tall. Pointed out it's not just the cost, but the hassle of install only to find out that the unit is ridiculously short-winded. Was assured that the $225 712 was much better. Do I trust 'em at this point?

Float Charge
Batteries must be maintained on float charge and should be fully recharged within 24 hours of any discharge.
The recommended float charge voltage is 2.23Vpc at 77˚F. Floating the batteries above 2.23Vpc may lead to overcharging; additional
watering be required as well as a shorter service life. Floating the batteries under 2.23Vpc without a regular equalize charge may lead
to reduced capacity, sulfation build-up and premature failure. For these reasons, we recommend 2.23Vpc @ 77°F, whenever possible.
The system float voltage should equal: (# of cells in system) x 2.23Vpc = System Float Voltage.
Float voltage should not vary by more than +/-1%. Should the float voltage of any cell vary by +/-0.02Vpc apply an equalize charge and
contact your sales office should this not correct the problem.
Float Charge Adjustment
The float charge voltage will need to be adjusted if the average operating temperature is above 86°F or below 50°F.
SBS does sell chargers that automatically compensate the float voltage with an increase or decrease in temperature; however, if you do
not have temperature compensation on your charger you will have to make the following adjustments to assure you are not over or
under charging the system: If the average battery temperature exceeds 86°F, the float charge voltage shall be reduced by
(AT - 86) x .003Vpc (but not less than 2.18Vpc).If the average battery temperature is lower than 50˚F, the float voltage shall be
increased by (50 - AT) x .003Vpc. AT=the average operating temperature.
Example: AT= 92°F: (92-86) x .003 = reduce Vpc by .018. A 60 cell system with a standard float voltage of 133.8Vdc (2.23Vpc)
should be floated at 132.72Vdc if the operating temperature is 92˚F.

[tanglewood]

For those of you playing with this remote sensing device, and discovering that it disconnects easily, is there any indication or alarm at the MPPT that the connection has been lost? Or does it just silently revert back to it's own local voltage/temp sense?