question

Trevor Bird avatar image
Trevor Bird asked

Smart Shunt "Charged Voltage" setting

The Charged Voltage setting on a Smart Shunt is important for the Sync function where the smartshunt deems the battery to be 100% charged when the battery voltage is suitably high and the charging current is suitably low.


The Smart Shunt manual says

7.2.2. Charged voltage

The battery voltage must be above this voltage level to consider the battery as fully charged. As soon as the battery monitor detects that the voltage of the battery has reached this “charged voltage” parameter and the current has dropped below the “tailcurrent [23]” parameter for a certain amount of time, the battery monitor will set the state of charge to 100%. Setting Default Range Step size Charged voltage 0 V 0V - 95V 0.1V The “charged voltage” parameter should be set to 0.2V or 0.3V below the float voltage of the charger. The table below indicates the recommended settings for lead acid batteries.


I think the manual may have a slight error where it advises the "Charged Voltage" should be set just below the Float voltage rather than the Absorption voltage. If the Charged Voltage is set below the float voltage the batteries are falsely synced to 100% well below a fully charged state. Surely the Charged Voltage level must be set just slightly below the Absorption Voltage to work correctly.

Keen to hear any views on this as I know of at least two cases where the advise in the manual has caused some real issues.

Trevor




SmartShunt
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.

3 Answers
Alexandra avatar image
Alexandra answered ·

@Trevor Bird

It depends on a number of conditions.

Since technically when a battery is floating it is fully charged as it has been through the whole cycle. But also needs the absorption to get there so other parameters are needed (tail current etc)

So won't falsely sync if the other ones are correct.

That being said there is a growing trend for lifepo4 to be slightly under absorption voltage. But then there are those who say lifepo4 does not need absorb and other no float.

Really it should be customised the way it works for you. The settings are a just a guide.

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.

pwfarnell avatar image
pwfarnell answered ·

Certainly if using limited solar to charge the batteries set the charged voltage to just below absorption because a poor solar day that generates a low charge current does not raise the charging voltage very high and is misconstrued as being full and synchronising. We wee this a lot with mobile systems on here. Suggestions to improve the manuals have been made in this respect.

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.

Trevor Bird avatar image Trevor Bird commented ·
Thanks @pwfarnell. I didn't realise the manuals were saying that because it makes no sense to me. We set systems up using the absorption voltage and really like how it works. Using the float voltage would create a disaster for us.
0 Likes 0 ·
Trevor Bird avatar image
Trevor Bird answered ·

@Alexandra I am asking as we have had to reset the parameter in marine applications because systems commissioned using the recommendation in the manual cause problems as they sync to 100% for battery banks that are not even close to 100%. If the battery bank is at say 30%, and the charging voltage is just above the "Charged Voltage" (just below float) and the charging source (maybe say an engine alternator) is just matching the DC current being used by other DC systems, the system syncs. When the skipper runs his generator to charge batteries at the end of the day, the generator is run for a ridiculously short time because the skipper thinks the batteries are full. The batteries die during the evening because they are taken down to zero and the terminal voltage falls away. I have seen it quite easily on VRM seeing very large house battery banks going from 20% SOC to 100% SOC in minutes with almost no charge current.

If the Charged Voltage is set to the Absorption voltage, the charging cycle must take the batteries to their fully charged state (absorption voltage with low tail current ) and no false syncing can take place.

This exact case is outlined in the video by Johannes Boonstra (https://www.youtube.com/watch?v=mEN15Z_S4kE) but is not given enough emphasis in the manuals as I believe certainly in the case of marine installations the advise on the Charged Voltage setting could cause very bad outcomes as I have recently witnessed

Thanks for your response.



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.