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btv128 avatar image
btv128 asked

Voltage drop when Smartsolar 75/15 disconnected from battery

My Smartsolar disconnected my 12V electrics yesterday, as the voltage had dropped below the thresholds I had set. So this morning, I set about charging my batteries using a mains charger.

I have everything set up so I can disconnect pretty much everything from the batteries whilst charging.

I can disconnect my split charger using a switch. And I can disconnect the battery +ve connection from the victron smartsolar to my batteries by pulling a fuse I put inline. I can also pull a fuse to disconnect my load.

Before I started, by voltage was reading 12.7V on both the victron and a battery monitor guage I have connected to the load.

I then pulled the fuse disconnecting the smartsolar input to the battery. The voltage then jumped to 13.8V, again both on the Victron app adnd my manual battery monitor.

I put the fuse back in, and sure enough it dropped back to 12.8v

Can someone explain what is going on here? Is the Victron dragging my battery voltage down to 12.7v, even though my batteries are actually 13.8v? Or are my batteries really 12.7V and need a bit of a charge? Or does disconnecting the feed to the batteries, somehow cause the voltage of the Victron load output to increase? Which is the true figure of my batteries?

Thanks in advance.

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3 Answers
Alexandra avatar image
Alexandra answered ·

@btv128

The battery needs a charge at that voltage.

The app will read higher at the mppt disconnected from the battery as it now no longer has the battery for reference. Are your loads still connected at this point?

To know what the true voltage of your battery is you should verify with a basic multimeter. When a battery is being charged the charge source has to have a greater voltage potential, this is my best guess. Battery needs a charge.

What are your settings? It also states it is in float so it is not actually trying to charge in this stage of the mppt cycle. So that is a bit suspicious.

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btv128 avatar image
btv128 answered ·

Thanks. The above was with load connected, although ultimately nothing would have actually been in use.

I've checked again this morning. Victron saying 13.46, multimeter saying 13.7.

Configuration settings attached.

Batteries are 2x travelbatt tb25mf

It had an update waiting, so have installed that.


On a more general level:

1. What voltage is 100% on these batteries.

2. What voltage is zero

3. I'm confused around measuring voltage. If I measure the voltage across the batteries, whilst the solar is charging, surely I'm just measuring the solar input voltage, not the battery voltage?

4. The same applies for my split charge relay. If engine is on, the victron batter voltage shows 14v, and the solar input always shows as 0w.

I guess I'm just a bit confused as to how to tell the real charge level on the batteries at any given time.

Thanks

P.S. I'll add pics from my pc to next post

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btv128 avatar image
btv128 answered ·

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