Dont understand my solar charging rate

[DavyS]

My motorhome has stood unused and unplugged from EHU for a couple of months so I thought I had better check the state of its batteries. The weather has been overcast recently but before then quite bright but the 160W panel obscured by frost.

It was the first sunny day for a long time but the sun was very low and weak.  The cab battery measured 13.8v; the hab battery 14.3v

I was expecting the batteries to be in need of a charge so I was very surprised by these high voltages. But perhaps I have misunderstood? The MPPT charge controller displays a solar panel voltage of 14.6v but maybe almost no current?

Could the charge voltage be 14v but the battery still flat cos no current?

I am new to this solar game so would welcome any thoughts.

[Derek Uzzell]

If your motorhome did not have a solar panel and it was unused and unplugged from an EHU, it's to be expected that the charge state of its leisure and starter battery would have reduced significantly (particularly the starter battery that would be maintaining the vehicle's electronics) after a couple of months. Measuring the batteries' voltage at that point would reveal what their charge state was. 

If the motorhome is then connected to an EHU, the motorhome's on-board charger will start to charge the leisure battery (and perhaps the starter battery too). The output from a charger will be from 13.8V to 14.4V and, if the batteries' voltage is checked while the charger is operating, it's the charger's output voltage that will be being read, not the batteries charge state.

It's much the same in your case - the 13.8V and 14.3V values are the voltages that the solar panel is providing to the batteries. They do not represent the batteries' charge state, as even a top quality fully-charged 12V battery will not have an 'at rest' voltage exceeding 13V.

If you want to know how well charged your motorhome's batteries really are, you'll need to switch off your solar panel, let the batteries 'rest' for (say) 6 hours and then measure the batteries' voltage. Or you could try starting your motorhome as, if it will start, its starter battery won't be flat -  and there's a fair chance the leisure battery won't be flat either.

[Thai Bry]

19 hours ago, DavyS said:

My motorhome has stood unused and unplugged from EHU for a couple of months so I thought I had better check the state of its batteries. The weather has been overcast recently but before then quite bright but the 160W panel obscured by frost.

It was the first sunny day for a long time but the sun was very low and weak.  The cab battery measured 13.8v; the hab battery 14.3v

I was expecting the batteries to be in need of a charge so I was very surprised by these high voltages. But perhaps I have misunderstood? The MPPT charge controller displays a solar panel voltage of 14.6v but maybe almost no current?

Could the charge voltage be 14v but the battery still flat cos no current?

I am new to this solar game so would welcome any thoughts.

My motorhome has been stood since coming back from a trip in November. Not on EHU at home. The van does have 2 x 100W solar panels.

Just checked and the charge on both the leisure batteries and engine battery is down to 12.4 volts. The display - DT2001 - is showing battery at 49%

I'll be putting it on the EHU just to maintain charge, before we use the van again mid Jan to early Feb 2023 

[DavyS]

8 hours ago, Thai Bry said:

The van does have 2 x 100W solar panels.

Just checked and the charge on both the leisure batteries and engine battery is down to 12.4 volts. The display - DT2001 - is showing battery at 49%

How did you measure the voltage on the batteries. Did you do what Derek Uzzell advised - disconnect the solar panels and rest the batteries for 6 hours?

[DavyS]

22 hours ago, Derek Uzzell said:

13.8V and 14.3V values are the voltages that the solar panel is providing to the batteries. They do not represent the batteries' charge state, as even a top quality fully-charged 12V battery will not have an 'at rest' voltage exceeding 13V.

So would it be true that solar in winter can generate 14.6v across a battery that is discharged without charging it?

[plwsm2000]

58 minutes ago, DavyS said:

So would it be true that solar in winter can generate 14.6v across a battery that is discharged without charging it?

Yes it is possible, but only if your battery is completely ruined and has one or more of its cells open circuit. In this case, the battery voltage will collapse as soon as you try to switch on any load (eg a light) assuming there is no solar or EHU.

If the battery is ok and fully charged, your solar will not produce any power even in strong sunlight as there is no load to drive. If you switch on a light etc. , you should then see some solar generation (if you have sun!) 

[spirou]

Not sure what the dillemma is. Yes, the solar panel won't be doing much these days, but still something. Quite possibly enough to maintain the charge state, especially if there are no significant loads on the battery. If the battery is full there won't be any current going in even under summer midday sun.

Whether all this means the batteries are in good health is another matter best resolved by simple tests already suggested above.

[colin]

2 minutes ago, spirou said:

Not sure what the dillemma is. Yes, the solar panel won't be doing much these days, but still something. Quite possibly enough to maintain the charge state, especially if there are no significant loads on the battery. If the battery is full there won't be any current going in even under summer midday sun.

Whether all this means the batteries are in good health is another matter best resolved by simple tests already suggested above.

As this, if as looks likely the solar has maintained charge, then on a sunny day there may well be a high voltage but little if any current.

[DavyS]

It seems that I am not really making my problem clear.

Before I had solar, I would monthly check the batteries voltage. If below about 12.2v then I would connect the EHU and charge the batteries.

Since having solar 5 months ago, I do the same monthly check. Each time the batteries voltages are about 13 to 14.5v. So OK then I dont need to connect the EHU.

However, in recent days the solar panel has been coated in snow, the weather cloudy or the sun very low. But I still get 14v at the battery terminals - so I dont need to plug in the EHU - or do I? Is the battery voltage not an indication of the state of charge; is it just the solar panel voltage? And almost no current being generated? So I do need to charge even if the battery terminals are at 14v?

If that's not clear then maybe I can make it simpler. Do you have solar? How do you check the state of charge of your batteries? Do you, as Derek suggests, disconnect solar and leave for 6 hours before testing. Bit of a faff?

Confused of what!

[BruceM]

I have solar (2 x 100w).

 

I don’t check the state of charge – that’s the battery chargers job.

 

So in the winter when solar charge may be abnormally low, once a month , I plug in to the EHU and leave it connected for 24 hrs.

 

As long as  the batteries are healthy (mine are only about five years old and unstressed) then there’s nothing to worry about.

[colin]

5 hours ago, DavyS said:

It seems that I am not really making my problem clear.

Before I had solar, I would monthly check the batteries voltage. If below about 12.2v then I would connect the EHU and charge the batteries.

Since having solar 5 months ago, I do the same monthly check. Each time the batteries voltages are about 13 to 14.5v. So OK then I dont need to connect the EHU.

However, in recent days the solar panel has been coated in snow, the weather cloudy or the sun very low. But I still get 14v at the battery terminals - so I dont need to plug in the EHU - or do I? Is the battery voltage not an indication of the state of charge; is it just the solar panel voltage? And almost no current being generated? So I do need to charge even if the battery terminals are at 14v?

If that's not clear then maybe I can make it simpler. Do you have solar? How do you check the state of charge of your batteries? Do you, as Derek suggests, disconnect solar and leave for 6 hours before testing. Bit of a faff?

Confused of what!

Solar still works under snow.

[Steve928]

On 12/22/2022 at 10:48 AM, DavyS said:

 How do you check the state of charge of your batteries? Do you, as Derek suggests, disconnect solar and leave for 6 hours before testing. Bit of a faff?

 

I don't physically disconnect my solar, I let the darkness do it for me. Usually I will check battery state before the day breaks and while the Votronic regulator is still in standby mode - that gives a true battery state reading as it will have been in standby overnight. 

My van is just outside the front door - it may not be so convenient for others of course.

 

P.S I'm referring to the depths of winter when the solar input is low - I don't get up at 3:00AM in the summer to check..

[spirou]

There's no need to wait until sunrise to check the voltage, a few hours after sunset is perfectly adequate and also avoids misreading in cases where there might be a minor load. And there's nearly always something that uses under 0.1A. Even the solar charger is never truly off and needs something miniscule on standby.

As far as snow on panels...depends how much snow and how much sun there is.

[Steve928]

1 hour ago, spirou said:

There's no need to wait until sunrise to check the voltage, a few hours after sunset is perfectly adequate

 

 

[Brian Kirby]

On 12/22/2022 at 10:48 AM, DavyS said:

It seems that I am not really making my problem clear.

Before I had solar, I would monthly check the batteries voltage. If below about 12.2v then I would connect the EHU and charge the batteries.

Since having solar 5 months ago, I do the same monthly check. Each time the batteries voltages are about 13 to 14.5v. So OK then I dont need to connect the EHU.

However, in recent days the solar panel has been coated in snow, the weather cloudy or the sun very low. But I still get 14v at the battery terminals - so I dont need to plug in the EHU - or do I? Is the battery voltage not an indication of the state of charge; is it just the solar panel voltage? And almost no current being generated? So I do need to charge even if the battery terminals are at 14v?

........................................................

I'm not "expert" in this field, but think the clue to your dilemma lies in Derek's post above (Tuesday).

Your batteries have two sources of charging power.  1 The on-board mains charger - which only operates when on EHU, and 2 your solar panels, which are permanently connected via the controller.

The problem with this arrangement (which is absolutely normal) is that the only source of information to your control panel is via the habitation, and starter, battery terminals - to which, of course, the sources of charging power are attached, but to which all your on-board consumers (e.g lights, possibly AES fridge controls and, in the case of the starter battery, engine management system, and possibly dashboard radio, etc) are also connected. 

So, when the EHU is connected, what the control panel will "see" is the charging voltage from the on-board mains charger and not the static, load free, resting voltage of the battery.  The same is true for the input from the solar panels.

To see the true state of charge on either battery you need to isolate the batteries from both sources of charging power and, ideally, also from the small background loads such as EMS, dashboard radio memory, and AES fridge controls, and then let the battery "settle" to lose its "surface charge" which is the product of the charging process and subsides over the course of a few hours until it reaches its true "resting" state.  You can then use a voltmeter onto the terminals of either battery to get an accurate reading of its resting voltage.

How you turn off the on-board charger, in the most simple way, is to disconnect the EHU.

How you turn off the inputs from you solar panel I know not (no solar!) but the solar controller manual should make clear.

The simplest way to isolate the on-board loads from the habitation battery is by removing the main (large, maybe 50A) 12V fuse that will be located near the habitation battery or, if you're lucky, an isolator switch.  Your motorhome manual should advise which, and where installed.

The starter battery should not be disconnected (too much essential electronics connected) unless a maintenance supply is available to keep the electronics supplies alive, so is best tested in situ, which should give an adequate indication of its state of charge.

I assume your main concern is the habitation battery, so you will need to isolate/remove both charging sources and, assuming the battery is installed under one of the front seats, the main 12V fuse should be on, or very close to, its "+" terminal.  As ever, proceed with caution and with the relevant manual/s to hand and, if unsure, leave well alone and seek advice from someone familiar with the make and model of your motorhome.

Also, it will help to get more specific responses to your battery query if you can state whether the habitation battery is a normal "wet" lead acid, gell, or AGM type, as each has different charging requirements and differing resting voltages.