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Traction batteries


Mickj

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Hi

 

I have a bank of 12 x 2v traction batteries new in July, 800 watts of solar and a victron battery monitor all work well, My question is what should the voltage be at 75% soc it shows 24v on monitor but all the info I can find out is they should be at a higher voltage at 75% soc

Thanks

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Hi

 

I have a bank of 12 x 2v traction batteries new in July, 800 watts of solar and a victron battery monitor all work well, My question is what should the voltage be at 75% soc it shows 24v on monitor but all the info I can find out is they should be at a higher voltage at 75% soc

Thanks

If they are reading 24.0v with no load they are not at 75% SoC. Your battery monitor presumes the capacity of the batteries is as programmed and so is not necessarily a good guide and certainly doesn't warn you that battery capacity is being depleted due to undercharging. The monitor may be set such that it shows 100% before it should do.

 

I would get a hydrometer (the optical ones from eBay are good) and check the specific gravity of the electrolyte. I have a nasty feeling that this will show the batteries are in a much lower state of charge than you think, and need a long charge to recover.

Edited by nicknorman
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but when was this voltage (24v) taken?

 

To get some indication of SOC from a voltage reading, the reading needs to be taken when the batteries are not being charged or discharged and have been 'rested' for a few hours.

 

The accurate way to know the SOC is as post #6, this does not of course indicate the capacity of the batteries, as mentioned in post #7.

 

If the batteries are true deep cycle, traction then taking them down to below 50% SOC may not be to detrimental.

 

A check of battery specifications and manufacturers guidance on charge and discharge would be advisable.

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I thought 12.7V on a 12V system was almost 100%, dependant on the battery?

And also in reply to Alan, I took the figure from a list I had copied down from a previous thread, I must have copied it put incorrectly. I shall now copy it once more.

Apologies for my error.

Phil

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What make & model is your battery monitor?

 

Bod

He said it was a Victron, but not which model.

 

These types of monitor determine when to show 100% charged by looking at the current and voltage. The general idea is that when the voltage is up at a charging-type voltage, and the current is down to a small percentage of the AH capacity set in the monitor, and this condition persists for a short time, the SoC is reset to 100%. Typically with an engine alternator or shore power charger, these devices are either on or off, with a corresponding step in the voltage so that the monitor can be clear whether charging is taking place or not

 

There can be a problem with solar however, since it is not just "on" or "off" but has shades of grey according to the sun/clouds etc. It is thus quite feasible that with sub-optimal settings for the target current and voltage in the monitor, as the sun goes in or a tree gets in the way, the voltage falls, but not so far as to go below the trigger voltage, and the current correspondingly decreases to below the trigger current, with this state persisting for a short time, the monitor resets to 100% even though the actual SoC might only be 75%.

 

From memory the default settings on Victrons are not well suited to solar.

 

The accurate way to know the SOC is as post #6, this does not of course indicate the capacity of the batteries, as mentioned in post #7.

It can be a good health indication though. If the battery appears fully charged (ie taking very little charge current at 14v +) but the SG remains low, this is a sign of likely sulphation.

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How many places after the decimal point does your voltmeter show ?

 

Assuming it shows 2 places, then your 24.00 volts is around 42-43% SOC. If they have been at that level for any length of time they may well not recover to full capacity.

And how accurate is it?

 

See if you can compare it with a really good one like a Fluke.

 

N

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Hi

 

Sorry have not replied earlier been moving boat, the batteries are also charged via fisher panda gene via victron 3000, the monitor is the latest one not sure of modal, the batteries read 2 volt to 2.1 volt at the batteries, when the monitor says 70/80% soc i float the batteries at least every other week, the readings are took under load IE fridge, freezer, sky etc I think it's the solar confusing the monitor, I don't let the batteries go under 23.90/24.00 volt before charging Thanks for all your reply's

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Hi

 

Sorry have not replied earlier been moving boat, the batteries are also charged via fisher panda gene via victron 3000, the monitor is the latest one not sure of modal, the batteries read 2 volt to 2.1 volt at the batteries, when the monitor says 70/80% soc i float the batteries at least every other week, the readings are took under load IE fridge, freezer, sky etc I think it's the solar confusing the monitor, I don't let the batteries go under 23.90/24.00 volt before charging Thanks for all your reply's

 

Unfortunately your readings are totally meaningless, you get usable measurements you MUST turn off everything electrical (Solar, battery charger, engine, fridge, freezer sky etc) and wait at least 2 hours before taking the readings.

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i have 12 x 2 volt cells but in 12v form one bank is 10 years old the other 3 - 4 years old at the end of a sunny day they show 12.8 volt at the end of the day winter i have to boost the solar with my wispergen for 3.5 hours per day. if you dont have a watering system on your batteries i would fit one makes life easier and helps the batteries to a 25 year life i hope

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