question

howie65 avatar image
howie65 asked

Absorption Voltage higher than set up - temperature compensation is not the reason

Hi there,

in my camper I substituted the PWM charger with a SmartSolar 100/20. Since then, my Whale heater signals frequently an over-voltage-error (>= 15V) despite that the absorption voltage is set to 14.4V.

A tracking of the battery voltage has shown, that there is indeed occasionally a spike up to 15V.

What can I do to fix the problem?

- Howie65


Additional information: the SmartSolar receives Voltage, Current and Temperature from a SmartShunt via Bluetooth. I did not test if this leads into timing issues.



2021-09-27-181204.jpg2021-09-27-174655.jpg


MPPT Controllers
2021-09-27-181204.jpg (3.3 MiB)
2021-09-27-174655.jpg (284.7 KiB)
2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

klim8skeptic avatar image klim8skeptic ♦ commented ·
What type of battery? Inbuilt BMS??
0 Likes 0 ·
howie65 avatar image howie65 klim8skeptic ♦ commented ·
it's a standard AGM with 95 Ah

no BMS

0 Likes 0 ·
4 Answers
Elimac avatar image
Elimac answered ·

These spikes seem related to some heavy load that is disconnected abruptly. If that is the case, it will be hard to avoid such transients. You could tackle it by making every effort to reduce the resistance in the DC side.

5 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

howie65 avatar image howie65 commented ·

At these days only the fridge is in use - don't know if this is heavy load.

Guess I have to record the battery current and the solar current in parallel with the voltage for getting a clearer view.

0 Likes 0 ·
Elimac avatar image Elimac commented ·

The battery might also be too small for the use case.

0 Likes 0 ·
howie65 avatar image howie65 Elimac commented ·

I don't want to talk here about the size or type of my battery - it is not the issue.

0 Likes 0 ·
howie65 avatar image howie65 commented ·

One important thing I considered just now: there was never a problem with the former PWM charger. Could this prove, that the SmartSolar is the problem and not the environment?

0 Likes 0 ·
Elimac avatar image Elimac howie65 commented ·
It can go both ways. PWM and MPPT are different animals. The PWM is more simple. One can argue that the MPPT revealed an hidden problem not visible with the PWM...
0 Likes 0 ·
howie65 avatar image
howie65 answered ·

I did more playing around with a 100 Watt load (8.5 A). It seems that the Victron Controller is very slow and this leads to swinging and even to oscillation. Is this strange behavior normal or did I receive a defect device?


controller-swings.png


controller-oscillates.png



controller-swings.png (233.2 KiB)
controller-oscillates.png (326.2 KiB)
controller-oscillates.png (326.2 KiB)
2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Elimac avatar image Elimac commented ·
Please check again your connections to battery and if battery is healthy. If the impedance seen by the MPPT to battery was low enough, I don't think you would see such high oscillations.
0 Likes 0 ·
howie65 avatar image howie65 Elimac commented ·

Everything checked and is ok. I decided to try another brand like Votronic or Buettner-Elektronik (I think they are in fact the same devices).


0 Likes 0 ·
Elimac avatar image
Elimac answered ·

What kind of battery do you have? Does it have any BMS ? Check your connections to solar and specially to battery. It still feels like it's either not the right size to stabilise the system or has to high resistance in the path.

It would also be interesting to know what kind of load is that.

AFAIK, MPPT implements a control loop. Oscillations can exist, but normally are dampen by battery, provided the impedance seen by MPPT is very small. Please someone correct me if this is wrong.

4 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

howie65 avatar image howie65 commented ·

The battery is a AGM with 95 Ah. The cables to solar and to battery are 6 mm². On rooftop there are two panels with 150 Wp each, connected in serial to the SmartControl.

Normally the loads are the devices in the camper, like Fridge, Diesel Heater, LED lights, Radio, etc.. Yesterday I used a Power-Station which can be charged by cigarette lighter plug (8.5 A, 100 W).

There are three points for measuring and comparing battery voltage: SmartControl (approx. 1,5m above the battery), SmartShunt (next to the battery) and a volt-meter (at the battery). Under load I cannot see noteworthy divergence between voltages. If high resistance exists, I would expect this.



0 Likes 0 ·
klim8skeptic avatar image klim8skeptic ♦ howie65 commented ·
Are you loads connected to the battery, or the mppt's load terminal?
0 Likes 0 ·
howie65 avatar image howie65 klim8skeptic ♦ commented ·

The camper devices are connected to the battery.

0 Likes 0 ·
howie65 avatar image howie65 klim8skeptic ♦ commented ·
On my yesterdays test I connected a load (charging cable of a power station) to the load terminal.
0 Likes 0 ·
howie65 avatar image
howie65 answered ·

In the meanwhile I changed the MPPT-Solar-Controller brand and the problem has been gone. Sometimes "Made in Germany" still seems to mean something ;-)


votronic-mpp.png



votronic-mpp.png (147.4 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.