danieldd0 avatar image
danieldd0 asked

Phoenix Multiplus Compact 12/1600/70 shows lower voltage than measured at terminals

For some reason the sales redirected me to this page - because its a private purchase no chance to get "official" support.It seems everything is locked to the sales chain - no chance for (re)using old stuff in a sustainable way of thinking.


I have an Phoenix Multi Compact 12/1600/70 in my camper connected to AC and with 2meters of 35mm² to a CSX12120-BMS120M Battery (LiFePo4).
No significant voltage losses on the battery lines (35mm³@2mtr with currents of 30A in this case)
Of course with main switch and extra fuse (175A) between.

For setup purpose I also have a datalogger running for the battery voltage added (battery terminal voltage) - it takes ~5 second snapshots.

The setup in multi is set to LIFEPO (the default) but with restricted charge current to 30A.(according manual of Battery)

For setup I have MKII and VEConfig running...

Currently the TempSensor is not connected, because the BMS in the Battery is anyway doing a compensation.

All measurements are done with good equipment (UNI T / Rigol scope etc)

Phoenix Multi Compact Plus 12/1600/70
On Processor: 1806130.HEX (also shows this in VEConfig)
Small Label: E56394
BigLabel 1A052056 CMP 1216/05100100062

Recognizable Behaviour:

Multi charges battery (with current of 30A as setup) and when internal BMS switches off (~14,5V) measured Voltage increase up to 15,5V
"float" is indicated with blinking yellow LED voltage sits on 16,5V - no current into battery.

When switching on loads on camper (eg. fridge / ~8.5 A) voltage drops shortly down (~1sec)
and charger pushes energy - Current is 8,5A on charger output, but still no current into battery)

All other "channels" work properly just the DC Battery channel is crazy !
This also has effects on the voltage thresholds of Inverter of course...
It switch to early off !

- The manual of battery says that this shall be avoided in means of BMS protection and lifetime.
Also the permanent high voltage @16,5 is not good for the remaining camper electric.

The Question:

Is there a chance to setup the maximum output voltage and make a correction of the additionally ~3V of "overcharging" ?

Would a "manual" battery profile do a better job here ?

Is there a chance for battery sense (by default there is none populated...) ?

Any other "tweaks" to change measuring float voltage ? (Such as calibration)
Anybody else out there with similar effects ?

Greets Daniel

chargerPhoenix Inverterbattery system voltage
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2 Answers
wkirby avatar image
wkirby answered ·

I also have one of these very old 18xxyyy units too. It also exhibits the very same problems that you describe.
The cause is that the values of the resistors have drifted over time as they age. When the resistor values in the Voltage measurement networks drift then the accuracy the measurements will be thrown out.
I did what you did and compensate the settings, but that only really worked for that specific temperature. On a hot day the readings drifted even further and caused higher battery Voltages that I was comfortable with.

The resistors could be replaced, but then the whole device would need to be calibrated again. As expected the tools and utilities for calibration would not be available to the public, so the unit would have to go to a service centre, not sure that's worth the costs.

It's a pity that these sort of things happen, rendering the device almost useless. Alas that is the behaviour of some electronic components.
When I have some spare time I might look deeper into mending my unit because it is a waste otherwise.

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danieldd0 avatar image
danieldd0 answered ·

Thanks for the confirmation of my feeling.
The drift was so ugly that I could not adapt all the settings any more.

I did some investigations on the controller board and found that PIN 7 of the PIC18F452 is the channel for reading battery voltage. First i had in mind that the switch before the voltage divider could have an issue but was not the case - on the top of the voltage divider was almost same voltage as on battery.

So I de-soldered R63 and R64 and the lower one(to GND) had a fatal drift the resistor code was 17kOhm and measurement was 11,8kOhm ! => changed with the next matching i had on my stock => now it works with +-0,2V difference which is fine for me.

Up to now i had only readings about high drift but never experienced to me .
I do electronics for ~40Years... / 23 of them as Electronic Engineer.

Resistors can't be meassured direct on the board, because sneaking currents (current injection into the Micro Pins!) change the value!

When figuring out take care that you do not load the two sine wave inputs (Pin 3/4) of PIC ! => As a result the Multi could try to change phase, frequency and/or amplitude of FetBridge output signal to (miss)match signal.
Faults here could lead to FetBridghe direct working against high power !

Also working in open Multi is exciting, use good isolated devices and never short something......

Greets Daniel

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wkirby avatar image wkirby ♦♦ commented ·
Thank you very much for letting us know your findings, that's some serious drift! I'm going to look into this myself. 17kΩ is an awkward value, but I have the full E24 range in stock, so I'll be able to get close with a combination of those.

Through hole components are a bit fiddly for these modern times, I much prefer surface mount. It will be a fun project and nice to get this unit working again.

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danieldd0 avatar image danieldd0 wkirby ♦♦ commented ·

sure in new designs we prefer SMD, because THT is extreme expensive already. I have tons ow this THT here.... but not that value exactly - of course - Murphy!

One advantage of THT is to be able to use realy 3rd Dimension of PCB making (second floor of electronics ;) ) But don't drift away with the topic.

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