18 replies to this topic

[Elliskwleisk]

I'm having a mental meltdown here as I'm trying to do some simple working out and I cant seem to fathom it out in my head.

The story is, I have a carcoon that I keep my mini in at the moment which runs off the mains and works fine. Next year, from about April till maybe September, I plan to keep my mini at work in its carcoon which is an outdoor one and will be outdoors, far from any mains power. So I'm trying to calculate what battery and solar panel I require to run the carcoons fans, 24/7.

I am already aware that I'll require a leisure battery due to the characteristics of the drain cycle that will be experienced.

I'm assuming that because the carcoon power adapted can run from the cars battery, the fans are 12V DC and I've read that the fans draw 220mA each.

What I am trying to work out is:

What size of 12V leisure battery will I require, referring to the amp-hours or watt-hours?

What solar panel will I require, referring to watts (as they all seem to be categorised by that)?

A link to eBay or a retailers website for either of the above would be greatly appreciated but I would also like someone to explain it to me or how to work it out if they are able to and can spare the time as I've let myself down, and my ol' physics teacher!

Many thanks in advance

[ACDodd]

The first thing to do here is measure the actual running current of the load. Once you know this ts straight forward to work out the watt hours. Avoid assumptions and use some real world figures.

Ac

Edited by ACDodd, 05 December 2015 - 07:33 PM.

[Elliskwleisk]

The first thing to do here is measure the actual running current of the load. Once you know this ts straight forward to work out the watt hours. Avoid assumptions and use some tea wold figures.

Ac

Thanks for the reply Ac,

How do I find that out - disconnect the mains and measure what current the fans are drawing from the 12V battery in the car?

[KernowCooper]

Yes exactly

2x 220mA fan connected to a 110 A/h Leisure battery(popular size) would run on a full charge for 220hrs, or around 9days.but that would be to flat, so I'd say about a weeks running.
How ever if you had access to a window and could run a 12v 1A/h (If bigger if funds allow)solar panel you could have a system that ran the fans and during light hours recharged the battery

Edited by KernowCooper, 05 December 2015 - 09:06 PM.

[Elliskwleisk]

Yes exactly

Ah okay, are we expecting that to be greater than the quoted 220mA?

[KernowCooper]

Check you may be surprised I have see claimed figures before that are way out, and because of quality control on cheap components the 2 /3/4 fan may all be different.

[Elliskwleisk]

Check you may be surprised I have see claimed figures before that are way out, and because of quality control on cheap components the 2 /3/4 fan may all be different.

Okay, will do. Could you explain how I calculate it once I've confirmed that figure?

[KernowCooper]

Its in the post above, but find the mA draw of the fans combined - say 500mA which is 1/2 a amp and divide the figure into to A/h of the battery so 1/2 Ah draw on a 110Ah battery would give 220hrs run time, but less as that would be to flat as I explained above.

This solar panel at 20w would give a maximum of 1.6amps so would do the job if you had 2 fans at 500mW and have reserve to keep the leisure battery topped uphttp://www.ebay.co.u...PsUYAvFVNr8u_Jw

Edited by KernowCooper, 05 December 2015 - 09:53 PM.

[tiger99]

But then you have to know what fraction of theoretical light input the solar panel gets, the charge imparted to the battery being directly proportional to that. The voltage is constant even in quite dim light, the current varies linearly with light intensity. That varies, over the day and over the year, with cosine of angle between perpendicular to panel surface and sun. So does the length of day. Then there is the weather, you may be down to 10% or less of theoretical current on a dark, cloudy day.

 

All of that is completely imponderable, so you really need to do some Googling for actual performance data and find out what average you will get, over the year, from your size of panel. You then need to check that it will have a high enough average, over the calculated battery discharge time as explained above by others, in the winter months to keep the battery topped up.

 

For instance, if your battery does indeed provide 0.5 amps, corresponding to the actual running current of your equipment, for 220 hours, that is 7.2 watts (at nominal 14.4 volts) so you need a panel specified to provide a guaranteed average (allowing for night, day and weather) of somewhere near 8 watts, even in mid winter. The manufacturers of solar panels "may" have such information, or you may have to do major overkill and get something like a 100 watt panel, which may manage barely 25 watts average on a clear winter 24 hour day or maybe at least 8 watts on a dull day. But there are no guarantees, weather being what it is, which is one reason why the government are utterly stupid in placing reliance on solar energy, or for that matter, wind. I think you may beed a 200 watt panel to be sure.

 

To do a calculation, you need facts, and they are in short supply here. Weather, for one....

 

Sorry, but that is how it is.

[Ethel]

Get a tent?

 

I'm only being partly facetious, it'd be worth having some sort of fail-safe, like a frame in case the fan fails, or the wind overpowers it.

[KernowCooper]

But then you have to know what fraction of theoretical light input the solar panel gets, the charge imparted to the battery being directly proportional to that. The voltage is constant even in quite dim light, the current varies linearly with light intensity. That varies, over the day and over the year, with cosine of angle between perpendicular to panel surface and sun. So does the length of day. Then there is the weather, you may be down to 10% or less of theoretical current on a dark, cloudy day.
 
All of that is completely imponderable, so you really need to do some Googling for actual performance data and find out what average you will get, over the year, from your size of panel. You then need to check that it will have a high enough average, over the calculated battery discharge time as explained above by others, in the winter months to keep the battery topped up.
 
For instance, if your battery does indeed provide 0.5 amps, corresponding to the actual running current of your equipment, for 220 hours, that is 7.2 watts (at nominal 14.4 volts) so you need a panel specified to provide a guaranteed average (allowing for night, day and weather) of somewhere near 8 watts, even in mid winter. The manufacturers of solar panels "may" have such information, or you may have to do major overkill and get something like a 100 watt panel, which may manage barely 25 watts average on a clear winter 24 hour day or maybe at least 8 watts on a dull day. But there are no guarantees, weather being what it is, which is one reason why the government are utterly stupid in placing reliance on solar energy, or for that matter, wind. I think you may beed a 200 watt panel to be sure.
 
To do a calculation, you need facts, and they are in short supply here. Weather, for one....
 
Sorry, but that is how it is.

The OP will have a brian shut down reading that post.

The charger is only required for April-September, not all years round and the cost of a 200w panel is far to much for this short term project, the car is question has no immobliser/alarm and I had a 20w one sitting on the dash of my Seat and it kept the battery up and did the job the OP is suggesting.

Edited by KernowCooper, 08 December 2015 - 07:28 PM.

[David128]

Don't you just love living in this temperate country...

[Elliskwleisk]

But then you have to know what fraction of theoretical light input the solar panel gets, the charge imparted to the battery being directly proportional to that. The voltage is constant even in quite dim light, the current varies linearly with light intensity. That varies, over the day and over the year, with cosine of angle between perpendicular to panel surface and sun. So does the length of day. Then there is the weather, you may be down to 10% or less of theoretical current on a dark, cloudy day.
 
All of that is completely imponderable, so you really need to do some Googling for actual performance data and find out what average you will get, over the year, from your size of panel. You then need to check that it will have a high enough average, over the calculated battery discharge time as explained above by others, in the winter months to keep the battery topped up.
 
For instance, if your battery does indeed provide 0.5 amps, corresponding to the actual running current of your equipment, for 220 hours, that is 7.2 watts (at nominal 14.4 volts) so you need a panel specified to provide a guaranteed average (allowing for night, day and weather) of somewhere near 8 watts, even in mid winter. The manufacturers of solar panels "may" have such information, or you may have to do major overkill and get something like a 100 watt panel, which may manage barely 25 watts average on a clear winter 24 hour day or maybe at least 8 watts on a dull day. But there are no guarantees, weather being what it is, which is one reason why the government are utterly stupid in placing reliance on solar energy, or for that matter, wind. I think you may beed a 200 watt panel to be sure.
 
To do a calculation, you need facts, and they are in short supply here. Weather, for one....
 
Sorry, but that is how it is.

Wow, that is one in depth answer! I really appreciate the time taken for you to tell me that.

There was me stressing over V=IR !!

Replying to the issues you have stated, I did think about the weather etc but as already mentioned, it is only from April to september, and that would be at a push. It's only so I can have it at work rather than using it five times a year! I'm hoping that if I get a slight overkill of a panel, that even if it's only light 1 day in 7, I'm hoping that it would produce enough to recharge the battery and keep the carcoon inflated.

It would be parked on the corner of an airfield so the actually sunlight would be permanent during daylight hours as there is no objects to shadow and obstruct it.

I did take in to account the manufacturer stated outputs. They do say that they are all tested at the standard 27 degrees celsius or something and Somerset is certainly no beach in Spain! So I was thinking on doubling the required solar panel size and going for a 40W bad boy.

Like this:

221401457064

If all else fails and we had horrid weather for a week straight or something, I do have the facility to recharge the battery but I'd prefer to not have to do this.

[KernowCooper]

10amps is up to the job of the fans and charging, the no charge time from the panel will be picked up for the fans ok

[Spider]

But then you have to know what fraction of theoretical light input the solar panel gets, the charge imparted to the battery being directly proportional to that. The voltage is constant even in quite dim light, the current varies linearly with light intensity. That varies, over the day and over the year, with cosine of angle between perpendicular to panel surface and sun. So does the length of day. Then there is the weather, you may be down to 10% or less of theoretical current on a dark, cloudy day.

 

All of that is completely imponderable, so you really need to do some Googling for actual performance data and find out what average you will get, over the year, from your size of panel. You then need to check that it will have a high enough average, over the calculated battery discharge time as explained above by others, in the winter months to keep the battery topped up.

 

For instance, if your battery does indeed provide 0.5 amps, corresponding to the actual running current of your equipment, for 220 hours, that is 7.2 watts (at nominal 14.4 volts) so you need a panel specified to provide a guaranteed average (allowing for night, day and weather) of somewhere near 8 watts, even in mid winter. The manufacturers of solar panels "may" have such information, or you may have to do major overkill and get something like a 100 watt panel, which may manage barely 25 watts average on a clear winter 24 hour day or maybe at least 8 watts on a dull day. But there are no guarantees, weather being what it is, which is one reason why the government are utterly stupid in placing reliance on solar energy, or for that matter, wind. I think you may beed a 200 watt panel to be sure.

 

To do a calculation, you need facts, and they are in short supply here. Weather, for one....

 

Sorry, but that is how it is.

 

On the surface of it, that seems to all be there, however just ask the manufacturer / supplier of the panel, they'll guide you as to what their product will and won't do.