Mystery Voltage drop.

[Longboard]

I have 2 100w solar panels charging 2 brand new 110 A Numax batteries in my (basic) self build.
For the first time the charge hit the controller limit at 14.5v (is that a good limit to set?) in the first strong sun it has seen. I was impressed.
Next day - in overcast - the batteries were reading 13.2v, even though I have had nothing in the van switched on.
Is this normal?
The only drain I can see is a digital voltmeter/power point, (no USB) and the Solar controller's lcd display. The leisure system is entirely seperate from the vehicle electrics. Surely these wouldn't take out more than 1v in a day? Would they?

 

[sparrks]

I have 2 100w solar panels charging 2 brand new 110 A Numax batteries in my (basic) self build.
For the first time the charge hit the controller limit at 14.5v (is that a good limit to set?) in the first strong sun it has seen. I was impressed.
Next day - in overcast - the batteries were reading 13.2v, even though I have had nothing in the van switched on.
Is this normal?
The only drain I can see is a digital voltmeter/power point, (no USB) and the Solar controller's lcd display. The leisure system is entirely seperate from the vehicle electrics. Surely these wouldn't take out more than 1v in a day? Would they?

A fully charged 12v battery is about 12.7v (from memory) so it seems the charge voltage is up to 0.5v higher so the batteries are still charging.

 

[Beemer]

I have one 100w solar panel and two 115Ah leisure batteries and my system has been 'online' for the past 2 years.
During this winter I often see no more than 13.5v maintained when the sun is not bright, more when it is, so your volts seems normal to me.

 

[Siimplyloco]

Do not worry....:dog:
John

 

[Wooie1958]

I have 2 100w solar panels charging 2 brand new 110 A Numax batteries in my (basic) self build.
For the first time the charge hit the controller limit at 14.5v (is that a good limit to set?) in the first strong sun it has seen. I was impressed.
Next day - in overcast - the batteries were reading 13.2v, even though I have had nothing in the van switched on.
Is this normal?
The only drain I can see is a digital voltmeter/power point, (no USB) and the Solar controller's lcd display. The leisure system is entirely seperate from the vehicle electrics. Surely these wouldn't take out more than 1v in a day? Would they?

The 2 figures ( 14.5v & 13.2v ) you saw are the output voltages from the solar charge controller going to the batteries.

On a bright sunny day you`ll get 14.4 /14.5v and likewise on a cloudy day you can still get the 13.2v that you saw.

To check the batteries they need disconnecting from the power supply ( solar panels ) and leaving a while to rest / settle.

You`ll then find that the voltage slowly comes down to approx 12.7v which is fully charged and then should stay there.

 

[Longboard]

Well I never ...

I had no idea that a battery should sit at 12.7.
But I'm confused - don't batteries start sulphating below 12.5v? This seems to give no leeway between full charge and minimum charge for actually using the things...
Can I really spend an evening watching some TV or using the laptop without 'bottoming out' in no time?
And, even more confusing- how do I know when I've reached the cut off point? Is it the 'voltage under load' I need to keep an eye on, or the voltage 'at rest'?

 

[Rob H]

Mystery voltage drop

Hi Longboard,

Your solar and battery system capacities seems very similar to mine, As others have commented and given advice your daily system voltages seem normal.

I have found my system has maintained my 2 x 90aH AGM's over the last three years 24/7, 365 days a year. My usage when touring is led lighting at night, 12v compressor fridge (of course over 24hrs this runs intermittently), 12v to 19v Computer power adaptor, Eberspacher when used.

You have 220 aH capacity in total. For your peace of mind, suggest you add up 1) Your total amp hours used during the day, and 2) Your amp hours used during the night, (when solar is not producing and solar controller switches to no charge). Compare this to your battery aH capacity.

I don't know your 12v electrical usage, (you don't mention whether you have a 12v to 240v ac inverter for your TV and computer, these are the devils devices and really devour big amps and will rapidly drain your leisure batteries, alternatives are available), so, your solar panels will probably keep pace with aH outgoings during each day, and, charge your batteries to max by evening, and you will be depleting your battery capacity at night. (The less % capacity your batteries cycle through per 24hrs the longer your lead acid batteries will last), so batteries subject to 20% depletion per night will outlive 50% depletion per night.

As for sulphating, your recorded voltages seem ok, check your solar controller manual, as high quality controllers have charge program options that optimally maintain your lead acid battery type, not overcharging, and, limiting sulphation, e.g. Wet, Gel or AGM programs.

Hope this puts your mind at rest.

Rob H

 

[Siimplyloco]

As I said earlier, do not worry...
John

 

[Longboard]

Thanks guys,
put my mind at rest!
I can't quite believe I didn't know about the voltage level after all the research I did before buying!
the only remaining niggle is: load and 'resting' voltage are different - so how do you keep an eye on your battery level to avoid overworking them? ( In other words - I can't trust my voltmeter to give a true reading when using tv/ computer etc )

 

[Rob H]

Mysery Volatge Drop.

Hi Longboard,

You have a preoccupation with voltmeters lol. Take a look at Battery Condition Indicators and their associated Shunts on the tinternet, and, DIY fitting for camper vans or marine usage. If you buy into these devices you will probably end up with a reasonably priced e bay Chinese made unit. These Shunts wire up to some pretty sophisticated Battery Condition Indicators that can display ( if you can manage to program them, because I found them a challenge lol). Battery Voltage, Current flow in amps into, or out of your battery bank, Remaining useful Leisure battery capacity as hrs, or % remaining.

As for not overworking your batteries, suggest if you do not drain your lead acid batteries faster than 10% of your total battery capacity, i.e. max, in your case of 20 amps drain at any time, or 20 amps charge at any time they should have a long life, (things that kill lead acid batteries are heat and excessive internal gassing at the plates from over charging or heavy discharging which dislodges the lead sulphide paste, and last but not least, vibration).

Happy researching.

Rob H