question

xrstokes avatar image
xrstokes asked

Multiplus Shifting to 52hz before charging complete.

I have 2x Multiplus 2's working in parallel to supply a single phase house. I have a PV inverter connected to the output and it is offgrid. The system for the most part is great and works a treat. But lately has been behaving strangely[could be hot weather]. During charging, when it reaches about 90% or has been in absorption for about an hour, it disables the inverter by going right up to 52hz. But it doesn't tell me why. Then after random amounts of time, comes down again. I've got no idea why. There are no errors in the ccgx. I've even tried pouring through the logs in /data/log. But there are no clues there that I can find. Refer to the pick, it always seems to happen about 90% SOC.


Multiplus-II
capture.jpg (78.9 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.

5 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

I am not seeing an issue with your graphs.

Remember the system does not use the state of charge at all, it is for your convenience.

The system is only looking at time, voltage and current when making charging decisions.

The system is reaching the target absorption voltage, the current required to hold it there is reducing to nearly 0. So it is telling the PV inverter to stop charging.

If the PV inverter was also supplying loads, then those will now come from the battery until the voltage drops again, and it allows PV inverters to generate again.


If your system doesn't ever reach 100%, there is possibly an issue with the battery monitors settings and it might need some configuration tweaks.

1 comment
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.

xrstokes avatar image xrstokes commented ·

It's done it again today. But I noticed this time it was following a large load cutting out. The charge rate had got down to 8amps and I used the microwave, the pv inverter ramped up to cover the microwave load and there was a very slight battery spike when the microwave cut out. Not enough for it to throw an error or message. But it's gone to 52hz as a result. Which is bad because now my pool pump has cut in and it is smashing the batteries. This is surely not meant to happen.....What triggers it to start the pv inverter again or what triggers the multi to lower the freq. Can this trigger be manipulated on the dbus so to stop this from happening. Other wise the batteries will never get to float, because it will just turn off the inverter during absorption.

0 Likes 0 ·
xrstokes avatar image
xrstokes answered ·

I thought it would keep the pv inverter going to supply the loads and keep the battery at float. So am I to understand that as long as there are loads, it will never actually get to float, just finish absorption and turn off for a little?

Seems like that could be improved a bit. It bit me in the bottom last night pretty bad. Between 3 and 6 is peak usage for us[electric oven]. But that is when it was having a break. Our battery dropped back to 70% in that time. Then the sun was gone when it turned back on. So started the night at 70% instead of 90....

Any chance this will ever change? it could have used the 3kw of pv for the oven instead of turning off for a bit.

Thanks for your reply BTW. I was thinking something was wrong.

1 comment
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.

Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ commented ·

In my experience AC PV inverters are often a bit rough like this. They can be quite clunky at the tail end of charging. They often have minimum outputs, and are quite large, with a delay in response.

This leads to a non-optimal tail end charging of batteries.

It seems a bit much that would discharge to 70% though, do you have a graph that occasion?

0 Likes 0 ·
xrstokes avatar image
xrstokes answered ·

I've tried some changes and it hasn't happened for a few days. In the ess assistant the freq shift was set from 50.2 to 51.8. In my inverter it was actually 50.2 to 52. The ess assistant wouldn't allow the stop freq and end of frequency shift be the same figure. I set them to 51.95 and 52. The problem hasn't reoccurred since then.


Finger crossed. Thanks for help so far.

1 comment
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.

xrstokes avatar image xrstokes commented ·

Still doing it today. :(

Got to 90%, turned off for 3 hours and didn't turn back on again till the batteries dropped to 77%. A disaster because the air conditioner was on during that time.

This has surely got to be looked at. I'll be on the generator tonight if I don't get anymore solar.

0 Likes 0 ·
capture.jpg (74.2 KiB)
boekel avatar image
boekel answered ·

Please post your battery settings, and what type of battery you are using.
Also check the 've-bus state' graphs.

I'm thinking it switches to float voltage and the float voltage is too low, the unit won't use PV power because it would cause the voltage to rise above float.

depending on what type of batteries you have you might use a longer absorption time / higer float voltage / etc.


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.

xrstokes avatar image
xrstokes answered ·

I have 16 of these batteries in 4 strings of 4. GEL/VRLA. I have a little voltage lcd on each one to see if they get out of balance, but they've been perfect. Hopefully you can help me work this out. Today it cut out for nearly 3 hours even though it never got to absorption that I can see. If you send me your details I'd be happy to share the installation with you in VRM.







capture.jpg (42.6 KiB)
battery-stats.jpg (109.8 KiB)
capture2.jpg (64.0 KiB)
capture3.jpg (27.2 KiB)
1 comment
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.

boekel avatar image boekel ♦ commented ·

the battery stats say charge to 14.7V 58,4V but this won't change much on the behavior. Did you try the 'batterysafe' setting (choose 'fixed')? by not using that it might switch back on voltage instead of some smart algorithm.

Do you have a BMV in the system? Your SOC is not correct, if the battery doesn't accept any current at float voltage it should be 90-95% charged. so the settings on the BMV or in the Multi should be looked at.

Your problem is: the battery is fully charged, it doesn't take more current, so the Multi has to stop the PV inverter from delivering power (maybe it can't throttle down low enough).

So the question here is: what mechanism is used to decide to switch back to charging: voltage, SOC, ??

What would certainly work: use (at least for part of the PV panels) DC chargers (Victron: MPPT's)

0 Likes 0 ·