Deep Cycle Batteries - Caring for Them

[Ashley Cawley]

I'm a novice to the whole photovoltaic scene, I'm wondering about buying a deep-cycle battery for a solar panel, I remember reading that you shouldn't really take your deep cycle battery below 50% of it's capacity/charge to maintain good condition, so to get double the capacity of battery storage than you'll actually need.

My question is how do you monitor the charge/status of your deep-cycle battery? I know there are charge-controllers etc. that control the flow and stop your batteries from being damaged by being over-charged but are there devices that will show their current charge/status?

[jus_young]

Hi Ashley

What type of system are you proposing to use ie. are you using the batteries to power 12 volt equipment or putting the batteries through an inverter to give you a 230 volt supply? This will affect what equipment you need including the capacity/charge status.

[jus_young]

You may find this document useful, free download, it is full of tech stuff including grid connected PV but there are sections relation to battery systems

http://www.bre.co.uk/filelibrary/pdf/rpts/Guide_to_the_installation_of_PV_systems_2nd_Editio n.pdf

Also check these for battery info including sizing

http://www.wirefreedirect.com/battery-capacity.asp
http://www.wirefreedirect.com/battery_sizing.asp

As you have said, in basic terms, a decent charge controller has three sets of contacts. One set is the input from your solar panels, another set of contacts go to the batteries to charge them as well as monitor the charge state/voltage and the last set provides you with the supply to power your equipment.

If the battery needs a charge then the power from the solar panel is diverted to the battery unless you want to use it. When the battery reaches its capacity then a trickle charge is maintained just to keep the battery in good order. When you want power the supply comes back up the battery connections, through the charge controller and out of the supply connections. If the charge controller senses that the voltage comming from the battery is too low then this supply is automaticaly disconnected to prevent deep discharging that would damage the battery.

Additional functions on a charge controller, providing it has an LED display, would include the present charge state and capacity.

Hope this helps, any questions chuck them at me, I may as well be useful for something!

[Ashley Cawley]

Hi Justin, thanks for your time & response.

...What type of system are you proposing to use...
For now I'm only talking about a small scale 12v system, well converting it using an inverter to 240v. If I had more money I'd go larger! But this is what I've got so far...

I've got a 13w Briefcase Solar Panel:
http://images.maplin.co.uk/300/n00cx_open.jpg Which can charges 3V, 6V and 12V appliances. Includes 4A charge regulator.

I've got a cheap/nasty 500w power inverter that I got from eBay (it's broke once & I've gone inside to resolder joints) seems to be holding up ok now.

The battery is basically where I'm lacking; I was using an old car battery for a while (which I knew was less than ideal) but now that's gone and I'm down to a small 12v 7Ah battery. I would love to get a 110Ah deep-cycle battery but I think they are a little too expensive for me at the moment. I used to know a place years ago where I could get a 110Ah deep-cycle battery for around £65! - But I can't find those sort of prices today.

Thanks for the documents & further reading I will be taking a look at them when I get a chance in a bit.
T^

Any further advice would be greatly appreciated.

[Ashley Cawley]

Oh and my use for this energy by the way is sporadic and changes locations: for example, I will use it in the shed or garden to run handheld grinders or bench grinders (only for short very durations), maybe a light, small fan for the forge, this isn't all at the same time I'll add!

And then I often take a solar/battery setup to the Royal Cornwall Show for 2 or 3 days where we've got a tent in the Countryside area, to run a laptop showing photos/videos.

[happybonzo]

There are various types of deep cycle batteries. The best are the Gel batteries. These are used by expeditions because some-one else is paying for them.Then we come onto the so called "Leisure" batteries. They have thicker plates and will stand a discharge to 60% to 70%
The best advice on batteries that I've seen is from Chas Sterling. (http://www.sterling-power.com/support-faq-2.htm) He is no mug and does know what he's talking about. He reckons that Varta lorry batteries are as good as anything. The reason being that they have a deeper "sink" to catch the crud that detaches from the plates during charging/discharging.
I don't claim to be an expert on this but I have been building my own Motorhomes for some 30 years.
I use solar panels and have found that a decent panel setup is at least 2 x 80w. This will allow me to stay off sites for 5 to 8 days at a time
As a battery bank I would suggest that 2 x 110A of battery is a good place to start. The problems come when people start hanging Inverters off the batteries to get 230vAC :D
As to what is left in the battery, then a cheapy multimeter will soon give you the answer. Theoretical maximum is, I believe 14.4v. In the real world 13.7v is fully charged and if it drops to 11.5v then you should not discharge the battery any further.
If you can rig up a split charger from your main vehicle battery, then you could be charging your spare battery as you go to the Royal Cornwall Show, the West Cornwall Pasty Co for supplies or Trago for a bargain :D

[Adam Savage]

An alternative that I found works well for 2ah and maybe 3ah is cordless drill batteries. I know these aren't going to be up to your needs, but they are designed to be completely drained from time to time, which actually helps maintain their life.

[jus_young]

The best advice on batteries that I've seen is from Chas Sterling. (http://www.sterling-power.com/support-faq-2.htm) He is no mug and does know what he's talking about... I use solar panels and have found that a decent panel setup is at least 2 x 80w. This will allow me to stay off sites for 5 to 8 days at a time
As a battery bank I would suggest that 2 x 110A of battery is a good place to start. The problems come when people start hanging Inverters off the batteries to get 230vAC :D
As to what is left in the battery, then a cheapy multimeter will soon give you the answer. Theoretical maximum is, I believe 14.4v. In the real world 13.7v is fully charged and if it drops to 11.5v then you should not discharge the battery any further.
:D

I will agree with you about the Stirling stuff. I have been using their inverter chargers for some off grid National Trust properties and they are first class bits of kit though not cheap! These are designed to work from a mains supply eg generator to charge the batteries for night time use (quieter!) so won't help you Ashley. The two battery setup will give you plenty of power particularly if you are going to use grinders but I would watch that 500W inverter as realistically it will probably only give you about 350W for any length of time before it burns out. The other thing to watch is that it will only provide a 'modified sine wave' to replicate a.c. which is ok for some stuff but not ideal for some I.T. equipment, battery chargers or even power tools. A 'true sine wave' inverter is far better.
With regards to using a multimeter for checking the battery state just bear in mind also that a reading of 12 volts might give you the impression that the battery is ok but as soon as any load is put on that battery the voltage will drop immediately, possibly below what a charge controller may have as its cut off point ultimately resulting in the supply being cut off. This is not a fault just science.

[jus_young]

These guys http://www.batterymegastore.co.uk/ are pretty good for parts

These guys http://www.quasarelectronics.com/index.html aren't bad either

[Ashley Cawley]

Thanks for the advice all, greatly appreciated.

I forgot to mention I've got a good multimeter and I'm familiar with the idea of actual voltage changing quite a bit under load & idle. I bought a brand new 12v 7Ah battery the other day which I think was at 14v ... and I know what you mean Justin about it cutting out (I've watched my inverter do this many times with poor batteries & I've watched the voltage at the same time).

I didn't know the 11.5v rule though - that's the kind of tip I was after.

I loosely knew of the sine-wave issue but don't know the science behind why it's different or how it damages certain things, I'm glad you told me to avoid charging other batteries or running IT equipment off it, that's got me worried about the laptop thing at the RCS now, is there some sort of plug I can plug into the inverter to modify the sine-wave? I'll be looking at all the links you've provided soon, thanks again!

[jus_young]

...I loosely knew of the sine-wave issue but don't know the science behind why it's different or how it damages certain things, I'm glad you told me to avoid charging other batteries or running IT equipment off it, that's got me worried about the laptop thing at the RCS now, is there some sort of plug I can plug into the inverter to modify the sine-wave? I'll be looking at all the links you've provided soon, thanks again!

I wouldn't worry too much about stuff being damaged, it just doesn't work. I believe some items have a tendency to start to overheat which will give you an indication that somethings not quite right.

[happybonzo]

The Inverter needs to generate a Pure Sine wave from the "off" There is no way of moderating it afterwards at sensible money. The more money you pay for an Inverter, the better sine wave will be; so Antares and Victron will be good enough to run anything but the ones from Wun Hun Lo of Shanghai may well not be good enough.
IIRC, the fussiest item that you can put through an Ineverter is a 230vAC fridge!