Battery life using inverter

[Buckman]

Yesterday I connected the new Naco 12v charger to the 12v AGM battery and selected 12v AGM. Before connecting voltage on battery was 12.3v.

Today I went and checked the battery and it is still reading 12.3v? Using a multi meter, I disconnected the charger from the battery and measured the voltage charge coming from the charger.

The voltage fluctuated between 0.4v and 14v. I would have thought it was to supply a steady voltage / current to the battery? I am not sure if the charger is faulty?

Please advise. Thanks.

 

[ProfJohnL]

Yesterday I connected the new Naco 12v charger to the 12v AGM battery and selected 12v AGM. Before connecting voltage on battery was 12.3v.

Today I went and checked the battery and it is still reading 12.3v? Using a multi meter, I disconnected the charger from the battery and measured the voltage charge coming from the charger.

The voltage fluctuated between 0.4v and 14v. I would have thought it was to supply a steady voltage / current to the battery? I am not sure if the charger is faulty?

Please advise. Thanks.

If the charger has any "smart" capability it will try to monitor the the state of the battery by periodically testing the terminal voltage of the battery. It can only do this by stopping the charger current momentarily , and to see how far the voltage falls. With your battery disconnected the voltage will fall dramatically, and its likely the control panel will show you have a battery fault or battery disconnected.

 

[Buckman]

If the charger has any "smart" capability it will try to monitor the the state of the battery by periodically testing the terminal voltage of the battery. It can only do this by stopping the charger current momentarily , and to see how far the voltage falls. With your battery disconnected the voltage will fall dramatically, and its likely the control panel will show you have a battery fault or battery disconnected.

Thanks for the input..Apologies for not making it clear. whether connected or disconnected the voltage still fluctuates between 0.4v and 14.4v?

 

[ProfJohnL]

If the voltage fluctuates down to 0.4V when the battery is connected, there is something wrong somewhere. How are you measuring the voltage?

 

[Buckman]

If the voltage fluctuates down to 0.4V when the battery is connected, there is something wrong somewhere. How are you measuring the voltage?

I am using a multi meter on DC. As said no difference whether connected to battery or not the voltage fluctuation stays exactly the same I made sure that there is a good connection to the battery terminals. Although unit is quite warm I guess this is to be expected. The charger has been connected to the battery for over 24 hours and no change in battery voltage.

 

[ProfJohnL]

If with the battery connected the voltage still drops to 0.4Vdc there is something very wrong!

Where are you measuring this voltage? On the battery terminals or on the chargers output terminals?

If this is on the battery lead post terminals, the battery is very definitely history.

If its on the terminal clamps, then I'd be looking for loose terminals or corrosion.

If it's on the charger terminals, then I would be looking a blown fuse or broken wire in the 12V feed from the charger to the battery.

And of course whilst I have explained how smart chargers have to periodically sample the terminal voltage, in this case it could be a faulty charger.

 

[JTQ]

Measuring the current, its value and "sign" would be very telling.
At the stated 12.3 volts, if the charger could push current at the battery it would be doing so.

As I frequently recommend, one of these cheapo current tester is a very valuable toy to have in your useful box, for just this sort of "12" VDC diagnostic investigation.
LINK

 

[Buckman]

If with the battery connected the voltage still drops to 0.4Vdc there is something very wrong!

Where are you measuring this voltage? On the battery terminals or on the chargers output terminals?

If this is on the battery lead post terminals, the battery is very definitely history.

If its on the terminal clamps, then I'd be looking for loose terminals or corrosion.

If it's on the charger terminals, then I would be looking a blown fuse or broken wire in the 12V feed from the charger to the battery.

And of course whilst I have explained how smart chargers have to periodically sample the terminal voltage, in this case it could be a faulty charger.

As per your previous post ref pulsing I rechecked everything and I had done everything about correct. I read the instructions again which was difficult due to the size of the print plus I read the bad reviews. Why can't they make the print a decent readable size.

I had done everything correctly and connected up correctly etc. however with this device you need to switch it on, scroll through the menu, switch it off and then switch it back on. At the initial first time switch on it goes into stand by mode. Second time it works okay. Battery us not charged up again!

Thanks for the help.

 

[Buckman]

Another question for the mathematical minded. 12v 95ah AGM battery. in good condition.

Using a 500 w inverter and powering a 130w unit, will the unit last 4 - 5 hours? Thanks

 

[otherclive]

Another question for the mathematical minded. 12v 95ah AGM battery. in good condition.

Using a 500 w inverter and powering a 130w unit, will the unit last 4 - 5 hours? Thanks

If you actually have the parts it would be interesting to compare the “theoretical “ duration against the actual duration. Two key unknowns being the battery capability to deliver current and the inverter efficiency.

 

[Buckman]

Its a Yuasa 95AH leisure battery.

Capacity (C20)	95 Ah
MCA	1050 A
CCA (EN)	850 A

 

[RogerL]

How long is a piece of string?

The State Of Health (SOH) of a battery gradually drops with repeated charges/discharges from 100% down to 50% which many consider an end of life figure - that SOH % approximates to the actual capacity of the battery compared to it's nominal rating - so a 95Ah battery with, for example 80% SOH, would only have 76Ah actual capacity.

If you flatten the battery over 5 hours the nominal capacity will be less than 95Ah as that was tested at the 20 hour rate, even assuming SOH 100%

 

[ProfJohnL]

Another question for the mathematical minded. 12v 95ah AGM battery. in good condition.

Using a 500 w inverter and powering a 130w unit, will the unit last 4 - 5 hours? Thanks

I would think a 95Ah AGM battery in good condition and fully charged should survive a 130W load for 4 to 5 hours, but as Roger L has pointed out, we don't know the efficiency of the inverter, so we cant factor in the real power losses of your inverter.

As the battery ages its ability to perform will diminish.

Just a note about inverters and transformers they are called a constant power converters. This means:

Power In (Watts) = Power Out (Watts)

It's also useful to know that Watts are the product of Voltage x Current (Amps)
For example your 130W consumption translates to

230V x 0.56A = 130W
12V x 10.8A= 130W

If they were 100% efficient that would be perfectly true, but Inverters and Transformers do incur some losses usually as heat so the true conversion is

Power In (Watts) = (Power Out + Power losses in transformation.) (Watts)

Unfortunately we do not know the power loss in Buckmans inverter, and as expressed in previous comments that can vary depending on the type of invereter he might have, and the work the inverter is having to do. However it will always increase the consumption from the supply.

All types of batteries exhibit some sort of discharge voltage curve. As they are discharged the terminal voltage they produce also reduces. Unfortunately this is not always a linear relationship, and when a battery is considered to be fully discharged it will still have some residual terminal voltage. Each type of battery and chemical composition does have some "typical" values that well documented.

For example, a 12V AGM battery exhibits terminal voltages as shown here:

Voltage	Capacity
12.85V	100% (resting)
12.80V	99%
12.75V	90%
12.50V	80%
12.30V	70%
12.15V	60%
12.05V	50%
11.95V	40%
11.81V	30%
11.66V	20%
11.51V	10%
10.50V	0%

It should be realised that as the battery voltage drops, the inverter has to change its transfer function to compensate, as it maintains the 130W output power.

Consequently with the battery fully charged the inverter will pull

100% charged 130W = 12.85V x 10.1A
0% charged 130W = 10.5V x 12.4A

Plus whatever the inverters inefficiency requires to be covered.

As the battery is discharging the current it needs to supply is creeping up, and as that happens the ability of the battery to maintain that current also reduces, which means for example

A 100Ah battery should be able to supply a current of 1A continually for 100 hours So the product of the current x the time represents Ah. but as the discharge current increases, You would expect a 10A current to be maintained for 10Hours, in practice it will be slightly shorter. 100A current is likely to be for significantly less than 1hour. Again the rate at which the discharge current affects the discharge time is dependant on the design of the battery, and how old it is.

 

[Buckman]

Thanks I just wanted a rough idea and I am now suitably informed.

 

[otherclive]

Thanks I just wanted a rough idea and I am now suitably informed.

As I said in #60 best to try it out for real now you have the kit.

 

[Buckman]

As I said in #60 best to try it out for real now you have the kit.

Hopefully do that sometime today as eventually managed to get the correct fuse and fuse holder for the cable that goes to the inverter. However usng a 45w appliance instead of 130w.

 

[otherclive]

Hopefully do that sometime today as eventually managed to get the correct fuse and fuse holder for the cable that goes to the inverter. However usng a 45w appliance instead of 130w.

Be interested in seeing the results. Good luck, have a FE ready😱🧯

 

[Buckman]

Time for an update. A Yuasa 95ah AGM 12v battery that is over 6 years old using through a Victron 500w inverter to 240v. Ran the 45w Smart TV today for 4 hours. At beginning battery was reading 12.6v and after 4 hours it was reading 12.2v. So quite pleased with the result.

Thanks to every one that guided me along the way. Only drawback is that Sod's Law will kick in and we will probably never have a power cut again!

 

[otherclive]

Time for an update. A Yuasa 95ah AGM 12v battery that is over 6 years old using through a Victron 500w inverter to 240v. Ran the 45w Smart TV today for 4 hours. At beginning battery was reading 12.6v and after 4 hours it was reading 12.2v. So quite pleased with the result.

Thanks to every one that guided me along the way. Only drawback is that Sod's Law will kick in and we will probably never have a power cut again!

A good outcome, thanks for the feedback. Don’t forget to top the battery back up😱

 

[Buckman]

A good outcome, thanks for the feedback. Don’t forget to top the battery back up😱

Just to add about 3 -4 years ago while in storage, the battery dropped down to about 6v as I forgot to switch off the 12v. I did not have a AGM charger so used the lead acid charger figuring I had nothing to lose. It charge back up to 12.6v and being using since. No doom and gloom there!

Yep it is on charge as I type.

 

[Buckman]

As a follow on for all the paraphernalia that we have bought I am thinking of a solar panel to recharge the battery. I already have the Truma charge controller so just need a suitable panel.

Mainly to be used a home, but could also be used in addition to the 100w that is fitted as standard on the caravan although at this point I am unsure how to connect it into the caravan as I do not want a permanent fit for obvious reasons. We don't really want to lug around the other 95ah AGM battery.

 

[JTQ]

The solar input can quite suitably be wired directly to the battery, that is through a protection fuse.

Practically, this could be done with a plug system permanently wired up and housed, or even mounted in the battery box. I would favour via a smaller pair of Anderson connectors, or the solar convention MC4 connectors, something definitely polarised so error proof.

Functionally, some solar controllers can be aware of other chargers also feeding the battery, say another solar system, and modulate their activity to suit.

Also, functionally the controller should be ideally close to the battery and the battery controller coupling made pre, and uncoupled post the connection of the controller to the panel.

However, the abundance of portable panels where the maker simply mounts them under the panel all wired up, and provides a long lead with clips etc to mount to the battery rather proves doing otherwise causes no harm.

Mounting the controller on the panel technically is way from ideal though practically useful. Not ideal on at least two counts.

One, panels get hot when working, so the panel fools the controller into thinking the battery is also getting hot, if it is intelligent enough to sense it, backing off the charge voltage accordingly, so potentially not fully charging, nor as promptly as it might.

Two, the controller's output voltage is what it determines the battery requires. However, because of the in-between run of cable, that is not what the battery will get; cable voltage drop.

If you get serious and seek to optimise things performance wise rather than budget wise, I would have invested in a better MPPT controller and optimise panel(s) to suit.

 

[Buckman]

The solar input can quite suitably be wired directly to the battery, that is through a protection fuse.

Practically, this could be done with a plug system permanently wired up and housed, or even mounted in the battery box. I would favour via a smaller pair of Anderson connectors, or the solar convention MC4 connectors, something definitely polarised so error proof.

Functionally, some solar controllers can be aware of other chargers also feeding the battery, say another solar system, and modulate their activity to suit.

Also, functionally the controller should be ideally close to the battery and the battery controller coupling made pre, and uncoupled post the connection of the controller to the panel.

However, the abundance of portable panels where the maker simply mounts them under the panel all wired up, and provides a long lead with clips etc to mount to the battery rather proves doing otherwise causes no harm.

Mounting the controller on the panel technically is way from ideal though practically useful. Not ideal on at least two counts.

One, panels get hot when working, so the panel fools the controller into thinking the battery is also getting hot, if it is intelligent enough to sense it, backing off the charge voltage accordingly, so potentially not fully charging, nor as promptly as it might.

Two, the controller's output voltage is what it determines the battery requires. However, because of the in-between run of cable, that is not what the battery will get; cable voltage drop.

If you get serious and seek to optimise things performance wise rather than budget wise, I would have invested in a better MPPT controller and optimise panel(s) to suit.

We already have a Victron MPPT controller connected to the 100w panel which is fitted onto the roof of the caravan. It was just a thought that maybe one day we would like to go off grid.

We could then take the portable 100w panel and controller from home and connect it direct to the battery although the mounted 1000w panel is already charging the battery. Basically 2 chargers to the same battery.

The advantage of the portable is that you could angle during the day to the sun for maximum input. At the moment it is just a bit of musing in case one day we do try off grid.

 

[otherclive]

We already have a Victron MPPT controller connected to the 100w panel which is fitted onto the roof of the caravan. It was just a thought that maybe one day we would like to go off grid.

We could then take the portable 100w panel and controller from home and connect it direct to the battery although the mounted 1000w panel is already charging the battery. Basically 2 chargers to the same battery.

The advantage of the portable is that you could angle during the day to the sun for maximum input. At the moment it is just a bit of musing in case one day we do try off grid.

With a portable you can angle as you say, but also move it as the sun moves around the caravan.

 

[JTQ]

The advantage of the portable is that you could angle during the day to the sun for maximum input. At the moment it is just a bit of musing in case one day we do try off grid.

Indeed and its quite doable, just don't leave it too long to try going off grid, you might discover the wonderful options it opens, and even find you like it.
Agreed not for all, but nearly exclusively our camping style.

edit: as an aside, in the shoulder seasons when chasing the sun , living with the long shadows that throws, I exploit my 25 m EHU cable to send my panels power to the controller in the van.
I am told it causes others amusement, me moving the panel into the morning and evening sun shine, keeps me active, another very big plus at my age, in my book .