solar panel varying voltage

[waffler]

Bought a 90 watt folding panel with controller attached. Delighted with output- tv and heater fan on and never less than 75% of battery left. I have noticed that when battery is charged the voltage across it varies. This means the Truma fan speed varies and the Truma water heater, on gas, switches on and off. Supplier of panel says varying voltage is normal as the controller discharges the battery when full by 0.2 volts to then recharge it. Any ideas?

 

[ProfJohnL]

Hello Waffler, The voltage output of the panel will vary according to the amount of light it receivces, so variable voltage will arise. what the charge regulator does is to prevent excesive charge being applied to the storage battery, so there will still be some voltage variation as the light intensity changes.
There are voltage regulators for DC systems, but to get 12V out of them you need to have a minimum of approximately 14V going in. This would mean with just a 12V battery and no charge available, the appliance would may only see about 11.5V on a fully charged battery and abviusly less as the battery voltage falls with use.
Some appliances may not work with low voltages. also the size of the regulator necessary to cope with a full 12V system could be quite large and would need to be well ventilated to cope with full current loads.
A slightly better solution, might be to fit smaller duty regulators just to those appliances where voltage variations create annoyance issues. But my previous concern about the regulator having about 2V insertion loss may still apply.
As far as I know ther is no one that produces a ready made 12V regulator module for this purpose.

 

[MichaelE]

Quick question? Do you have the same problem with the panel disconnected?

 

[lgvdriver]

Hi guys, I was reading on the forum about putting an in line fuse next to the positive
terminal. I have one of the small solar panels from maplins just to keep my battery up
for the alarm, could you please tell me what size of fuse do I need. Ta.

 

[ProfJohnL]

Hello Dougie,
I dont have enough information to advise.
I assume you are refering to putting a fuse in the wires to the solar panel. in which case we need to know what wattage your panel is?

 

[mat1]

I have noticed that when battery is charged the voltage across it varies.

This is normal.
It is the charge controller preventing the battery from being over charged.
Mine for example will charge to 14.4v then drop to 13.1v then fluctuate between the two.

Mat

 

[lgvdriver]

Hello again prof John, sorry I didn't get back to you last night
but I had to run up to my storage today to see what the wattage is on
my panel, it is only 1watt and when I looked at it I saw that there is a 1amp
fuse fitted to th positive lead, so now I know.Now instead of hardwiring the
panel can I just use the twelve volt ciggy plug that comes with the panel to
Trickle feed the battery. Your advice appreciated.

 

[mat1]

can I just use the twelve volt ciggy plug that comes with the panel to Trickle feed the battery.

You can but you may find that the feed from the battery to that outlet is only live when the master switch is on.
If this is the case then anything that your solar panel puts in will be lost due to other sources becoming live.
If i may be honest with you the size of panel you have will not even cover the natural dischage of your battery.

There is lots of information on this forum which will be of interest to you if solar is your future project.

It is all about managing your expectations and what you actually want to achieve.
As a rough guide you will need 10 watts panel per 100ah battery size, and that is just to overcome the natural discharge, in storage for example, in this country throughout the year.

So you will see that a 1 watt will not really make a difference, in real terms.
Even more so that any light will be defussed as it passes through a window you put the panel behind.

Mat

 

[lgvdriver]

Thanks for the advice Mat, looks like il have to get a 10 watt panel,never thought about leaving the
master switch on! When I purchase a new panel it will be wired straight to the battery.again thanks

 

[lgvdriver]

Hi again, at the back of my12v socket there are 2wires 1white1yellow can
you tell me which is live, thank you

 

[waffler]

Thanks for responses. Just come back from a rally without EHU. Telly on every night 6 to 10 Fan on heater when needed and lights galore. Battery never dropped below 50%. The panel coped well even on the day when it rained all day.;

 

[mat1]

Hi again, at the back of my12v socket there are 2wires 1white1yellow can you tell me which is live, thank you

An educated guess this.
If you look at the back of the socket, one of the wires will be connected more central than the other.
The more central is the positive.

As for the solar panel.
If it is to do no more than maintain the battery whilst in storage then build in a 50% margin and go for a 15watt panel.
You will need a charge contoller, of 10 amps or more for this.

Mat

 

[ProfJohnL]

Hi again, at the back of my12v socket there are 2wires 1white1yellow can you tell me which is live, thank you

An educated guess this.
If you look at the back of the socket, one of the wires will be connected more central than the other.
The more central is the positive.

As for the solar panel.
If it is to do no more than maintain the battery whilst in storage then build in a 50% margin and go for a 15watt panel.
You will need a charge contoller, of 10 amps or more for this.

Mat

Hello Mat,

10A or more ??? - A 15W solar panel producing 15V will only produce 1A of current! - Basic Electrical calculations.

Where it is feeding a battery that will already have some standing voltage the current will be much less.

 

[mat1]

Hi again, at the back of my12v socket there are 2wires 1white1yellow can you tell me which is live, thank you

An educated guess this.
If you look at the back of the socket, one of the wires will be connected more central than the other.
The more central is the positive.

As for the solar panel.
If it is to do no more than maintain the battery whilst in storage then build in a 50% margin and go for a 15watt panel.
You will need a charge contoller, of 10 amps or more for this.

Mat

Hello Mat,

10A or more ??? - A 15W solar panel producing 15V will only produce 1A of current! - Basic Electrical calculations.

Where it is feeding a battery that will already have some standing voltage the current will be much less.

A 10A controller will give a built in expansion capability of his solar capacity, should he need it.
At the moment it appears requirments are for trickle charge, but when the vurtues of solar are realised, he may wish to upgrade and have a much larger panel roof mounted, for example.
Buy a larger charge controller now instead of again later. They are not expensive, and a good one is cheaper than buying twice.
The higher the capacity of the controller the better quality and more efficient use of the solar power, MPPT for example.
It is the same when people ask what size of cable to buy.
You over size to reduce voltage drop, do you not ? rather than what you actually need to do the job.

I am simply offering advice based on my experience.

Mat

 

[lgvdriver]

Hi again prof John and Mat just purchased a 13watt solar briefcase and a 12v-7amp charge regulator
as I said before its only to keep my batt up to charge when van laid up and using alarm.
again I thank you both, this forum never let's you down if you've a problem. TA