I have this strange little problem. When I go into the accu settings on the MPPT and set absorption voltage to 14.40V and Trickle voltage to 13.60V the Mppt gives a reading of 14.50V in absorption and 13.70V in trickle mode in the app. I first thought it was due to a voltage drop over the wiring but when I measure tension on the accu it is indeed 0.10V higher then te setting in the mppt. So for now I have set the values 0.10V lower but I was wondering if this was normal. It seems a bit strange to me when I set certain values the output is 0.10 V higher…
I also tried switching off al other things that could charge the accu so I only had solar panels and mppt going to accu but it stayed the same 0.10V difference in setting and actual output…
Does anybody have an idea what the cause could be?
One cause is temperature compensation and a battery temperature below 25degC.
Thanks, It had indeed to do with temperature compensation. Which brings another question. I have AGM batteries which are located in the same room as the mppt. I have no temperature sensor on the batteries. I can use the temp compensation but it will use the internal temperature of the mppt, not the batteries.
Is it better to disable temperature compensation and use fixed values for loading or Is it better to leave temperature compensation on for AGM even though it uses the temp of the mppt (located about 1 meter from the batteries) Batteries are located under a closed off seat and mppt is located behind the driver seat.
I think there can be difference in temperature in summer because temperature underneath seat will be lower than behind the driver seat.
Is this really important for AGM deep cycle?
And in the data sheet it says “The voltage is adjusted by the formula: (-5mVx(T battery - 25°C))” I think this means -5mv/°C but isn’t this a little bit low?
The MPPT takes the temperature at dawn before the MPPT has started to charge and warm up because the internal temperature increases as power increases. The choice of using temperature compensation depends then on how different your battery temperature varies during the day from the MPPT temperature at dawn. You could choose to disable it. The only warning is if your batteries can get very warm, 35 to 40degC, it is important to reduce voltage in this case as the batteries can heat up further and enter a self reinforcing overheating. You could use a Smart Battery Sense if you have the SmartSolar version connected by Bluetooth. The 5mV/degC is per 2V cell, so for a 12V battery it is about 30mV/degC.
Ah ok, interesting. So the MPPT only takes one measurement at the start of the charging cycle and that’s it. It keeps this setting until next day at dawn?
I have got this system for over 7 years now and it was always on a pre defined setting (I think 16mV/°C) , I never messed around with these things but I recently fitted two new batteries and was looking into these settings to see if I maybe could prolong life of these new batteries. So I was wondering if it took 7 years for me to really notice that my batteries lost capacity on a standard pre-defined setting will it make a big difference if I use the temp compensation? (Unless the temp compensation is switched of in the predefined settings)The temperature of 35 to 40 almost never happens, maybe once a year on a very hot day when I have no choice but to stand in full sun.
Also, is there a way to connect a temp sensor to the mppt or another option to do this without using bluetooth? For example, is it possible to connect a smart shunt with a sensor or a smart battery sense to the mppt with a VE. direct cable? Or is there another possibility?
If you got 7 years from a set of AGM you looked after them well, I am not sure you will get much more life from them changing things.
The only way to get the temperature into the MPPT is
- Bluetooth from Smart Battery Sense or SmartShunt.
- VE Direct cable from a GX device like the Cerbo GX and a temperature sensor on the Cerbo. A Raspberry Pi may also.work but I do not know how to add temperature sensors to them other than by VE Direct cable to a SmartShunt. You are adding lots of extra cost here.
So if I understand correctly, the only way to get temperature or other data from te batteries into the MPPT is via bluetooth and if I don’t want to use bluetooth but do everything with cables I need a Cerbo or other GX device which will indeed cost 300+ euro?
Hmm, It’s a shame it can’t be done via a VE.Direct cable between a smart shunt and an MPPT… I think this should be easy to adjust in the software… perhaps Victron could make this possible…
Yes, you are correct.
Ok, so in conclusion. If I do not want bluetooth but still want to look after my batteries the best way possible I was thinking to change out my smartshunt with a BMV-702 which will allow me to check status of my batteries. Only thing which is not possible in this scenario is the option to add a temp sensor to send temp data to the mppt.
But I see that the BMV-702 has a connection for a temp sensor, what is this for if it can not send data to the mppt?
The BMV-702 has a temperature sensor option, but it does not have Bluetooth so it can only transmit the data via VE direct to a GX device. A BMV-712 has Bluetooth, but I believe the Bluetooth is in the display unit so that would need to be in range of the MPPT.
Victron equipment is set up as small systems use VE Smart Network over Bluetooth, larger systems use a GX and wired connection. VE Direct does not support device to device connection, only GX to device.
I have just read that tje Smart Battery Sense does not support temperature over Bluetooth.
I understand, I would use the BMV-702 to monitor battery charge and discharge to know at what percentage I am as this is more accurate than just looking at the voltage. In this way I can take better care for the battery.
The ideal would have been to add temperature sensor for accurate temp compensation but since this is apparently not possible without the use of bluetooth I will have to leave it like it has been and trust on the MPPT for this temperature measuring at the start of each cycle. (Or does the MPPT keep measuring during the coarse off the day to adjust this?)
I would like to get rid off the bluetooth because I have found out it causes problems for my health. I live in my campervan and recently I noticed the health issues went away when I had to live and sleep a couple of months in another place because the van had to be repaired. When I got the van back, within a week I had the same health issues. So I searched an searched and never thought it would have been bluetooth, until I switched all bluetooth off, after 3 days health was ok.
So that is why i would like to do everything by wires…