How low to go with the voltage

[simonfraser]

Eber D2 fan on low and not much else on the batteries
220 Ah total capacity from a set of batteries now down to 12.2 V 5C here
So, how low should i run this before starting the KAD 44 to charge ?

 

[PaulRainbow]

Eber D2 fan on low and not much else on the batteries
220 Ah total capacity from a set of batteries now down to 12.2 V 5C here
So, how low should i run this before starting the KAD 44 to charge ?

12.2v is as low as i'd want to see my batteries. If you turn the Eber off the voltage display will rise a little, but i'd still be starting the engine now, nothing to gain by putting it off.

 

[simonfraser]

http://support.rollsbattery.com/support/solutions/articles/10372-voltage-readings-state-of-charge

This suggests under load 12.06 = 75% charged, no mention of the load ....

 

[RichardS]

This suggests under load 12.06 = 75% charged, no mention of the load ....

That would have to be a pretty large load to bring down the voltage that far ..... between 5A and 10A at a guess. I don't know whether an Eber draws 7.5A?

Richard

 

[lpdsn]

http://support.rollsbattery.com/support/solutions/articles/10372-voltage-readings-state-of-charge

This suggests under load 12.06 = 75% charged, no mention of the load ....

In the end it depends upon how much you want to mollycoddle them or absuse them, which in turn depends upon how keen you are to push back the expenditure on a new set. I'd go with PaulRainbow's advice, but I appreciate running a large engine to charge batteries has its own downside. You might want to look at alternative charging methods if you plan to run the Eber off the batteries regularly.

 

[PaulRainbow]

They say "as much load as possible". You are imposing a very small load. If you turn off all loads and check the voltage reading after 15 minutes it won't have gone up by much. The greater the load, the more the voltage reading will increase if the batteries are allowed to rest. With a 12.2v resting voltage your batteries will be around 50% SOC, the load you are imposing is small, so i'd say you are getting close to that now.

All assuming you have standard wet cell lead acid batteries.

 

[PaulRainbow]

That would have to be a pretty large load to bring down the voltage that far ..... between 5A and 10A at a guess. I don't know whether an Eber draws 7.5A?

Richard

Noooooooooooo. If it's a D2, at low power, 0.6a. It only has to run a small fan at slow speed. It only uses 2a at high speed. This is why i say that if he turns all loads off the voltage readings will barely rise, he's already run his batteries down to very, very, close to 50%.

 

[simonfraser]

Tnx guys, yeh just looked back at some other voltage readings from the same batteries and they were significantly higher in the spring, when it was also cold.
They came with the boat, so no idea how old the lead acids are.

Shall order a new set as they dont last forever and the labels on the existing ones are curly at the edges.

Interestingly after 4hrs still reading 12.20 V ....
I’ll run the engine b4 bed time

 

[bedouin]

12.7 they're in heaven
12.5 they're still alive,
12.2 charging due,
11.8 is much too late.

 

[lpdsn]

They came with the boat, so no idea how old the lead acids are.

Have you been able to check the water levels in each cell?

 

[ltcom]

don't know if these charts are of use?


But other charts show other things......

https://www.google.co.uk/search?q=b...KEwj34PbSp8nXAhXDuhoKHVcyDToQ9QEIKjAB#imgrc=_

 

[simonfraser]

Have you been able to check the water levels in each cell?

Green eye on both, only for one cell of course.
Sealed.

I made a note of the cranking voltage very early this year, 10.5, now its 10.0

As another poster said, D2 just ticking over, should be using no more than 1A
so assuming the alternator does charge properly, showing 13.7V with the engine on, the voltage should not be 12.2V after 5 hrs of the D2 ticking over

 

[PaulRainbow]

Green eye on both, only for one cell of course.
Sealed.

I made a note of the cranking voltage very early this year, 10.5, now its 10.0

As another poster said, D2 just ticking over, should be using no more than 1A
so assuming the alternator does charge properly, showing 13.7V with the engine on, the voltage should not be 12.2V after 5 hrs of the D2 ticking over

If your alternator is only charging the batteries at 13.7 volts you have a problem, your batteries will never fully charge. Do you have a split charge diode by any chance ? Can you check the alternator output at the alternator ?

 

[simonfraser]

Also have a 120W solar cell with a charge controller

No split charge, alternator output, V or A ?

 

[Bow42]

On another note ,
display that show SOC as in the BM1 would you consider the Voltage a more accurate reading of the state of the batteries then the reading % of SOC display ?

 

[macd]

display that show SOC as in the BM1 would would you consider the Voltage a more accurate reading of the state of the batteries then the reading % of SOC display ?

The rested voltage is a reasonable indicator of state of charge. But who wants to sit shivering in the dark while the batteries rest? Battery monitors are generally more convenient and reliable. As is implied in the discussion above, both V and A tell parts of the story but need a little interpretation.

 

[GHA]

The rested voltage is a reasonable indicator of state of charge. But who wants to sit shivering in the dark while the batteries rest? Battery monitors are generally more convenient and reliable. As is implied in the discussion above, both V and A tell parts of the story but need a little interpretation.

If they've had a load for a while to get rid of any surface charge then the resting voltage actually springs back up quickly once the load is removed, it's when they've been on charge that it takes forever for the voltage to stabilise. You can see the fridge cycling here, and 10pm when the laptop was turned off..

And here you can see it takes quite a while to remove the surface charge and for the voltage to stabilise even with a 3 - 5A load. 2 x T105 trojans. End of the day voltage just isn't a very good indicator if state of charge, you need to factor in temperature as well.

 

[simonfraser]

If they've had a load for a while to get rid of any surface charge then the resting voltage actually springs back up quickly once the load is removed, it's when they've been on charge that it takes forever for the voltage to stabilise. You can see the fridge cycling here, and 10pm when the laptop was turned off..

And here you can see it takes quite a while to remove the surface charge and for the voltage to stabilise even with a 3 - 5A load. 2 x T105 trojans. End of the day voltage just isn't a very good indicator if state of charge, you need to factor in temperature as well.

Tnx, v informative.
What kit do you use for this ?

Have just ordered a clamp meter to see what is going on with the current draw at least.

 

[GHA]

Tnx, v informative.
What kit do you use for this ?

Have just ordered a clamp meter to see what is going on with the current draw at least.

Raspberry Pi runs 24/7 onboard doing all sorts of useful things
Volts are measure with a little ADS1115 board , costs less than a fiver and very accurate, very useful.
Clamp meters are great!

 

[PaulRainbow]

Also have a 120W solar cell with a charge controller

No split charge, alternator output, V or A ?

Measure the voltage at the alternator, if it's only the 13.7v you mentioned earlier, that's not ideal, that won't fully charge the batteries. Check the solar controller output whilst you are at it. When taking readings, do the solar controller with the engine not running and the alternator with the solar controller disconnected (should be a fuse to pull). If your solar controller detects battery voltage (such as the Victron) disconnect the panel input to the controller, not the battery.