Running Upcycled Obsy with Solar?

[Chris]

Hi, I'm seriously thinking about running my newly built upcycled RoR obsy off solar, I'm just not sure if my plan will work as it seems too simple to be true? I'm not that clued up with electrical engineering so thought I'd ask for a bit of help with this.

My plan is to buy something like this 20W 12V solar kit plus a 12V leisure battery to run my EXOS2 mount and maybe LED lighting?

https://www.amazon.co.uk/Monocrystalline-Charge-Controller-Extension-Battery/dp/B07RZBVTGR/ref=asc_df_B07RZBVTGR/?tag=googshopuk-21&linkCode=df0&hvadid=375423088030&hvpos=&hvnetw=g&hvrand=17417217163303623566&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045074&hvtargid=pla-843716935674&psc=1&tag=&ref=&adgrpid=82457260731&hvpone=&hvptwo=&hvadid=375423088030&hvpos=&hvnetw=g&hvrand=17417217163303623566&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045074&hvtargid=pla-843716935674

Am I missing any vital ingredient?

Thanks

 

Edited November 15, 2020 by Lockie

[fifeskies]

All comes down to how often you use your gear and for how long.

Throw into that how much sun does your location get.

Also this "20w" panel will not output anything like 20w unless it is in the Sahara with the sun directly overhead.  😜

 

You may need to look at a bigger panel for this to be a realistic proposition.

 

 

Since you probably use the telescopes most during winter take a look at this information about the much lower winter output levels of solar panels.

Try to estimate how many Wh you will need.

At 12v running 1 amp for an hour is 12Wh , for a 4 hour session this becomes 48Wh.

 

If you use dew heaters and 12v camera supplies as well as your mount then you can easily be drawing 2-3 amps.

(so 24-36Wh every hour   144Wh for a 4 hr session.)

In winter even a 150w panel does not produce 144Wh on an average day.

 

A leisure battery can power everything easily but you will probably need to take it indoors to recharge after a session or two unless you have a large charging solar panel.

 

 

But a trickle charge from a solar panel will help reduce how often you need to take the battery indoors for a full recharge.

 

Edited November 15, 2020 by fifeskies

[Chris]

Thanks, that's great info Well I estimate the mount uses about 3amps, I don't use dew heaters but will be getting a dew shield for my 8" RC. The camera is stand alone off a battery or my planetary cam runs via my laptops battery. I guess it's just LED lighting and the mount, so I'll probably need something like at least 15Watt hours at a guess? I estimate I would use the obsy about 3 hours a week on average so hopefully plenty of time for a trickle charge. I guess if I got a large leisure battery for some head room that might help.

 

I could get this 30 Watt kit and a good battery perhaps:

https://www.photonicuniverse.com/en/catalog/full/142-30W-12V-solar-charging-kit-with-5A-solar-charge-controller-and-battery-cables-with-crocodile-clips.html?gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_Hrw9vig2RqPR7Zll621rf_H6ZXmcZ9lb5-UpwuzkQBxM357KCN44YaAsf6EALw_wcB

Edited November 15, 2020 by Lockie

[fifeskies]

If you are using 3 amps continuously

3 amps x 12 volts is 36Wh , every hour

x 3 hours is  108Wh.

 

that said your mount will not be using 3 amps if it is just tracking , maybe if slewing in RA and DEC at the same time.

 

 

also leisure batteries will often be rated in Ah     (amper hours)   

at 12 v , 1 Ah is the same as 12Wh.

 

Edited November 15, 2020 by fifeskies

[Davey-T]

Hi Chris I use a 25 watt solar panel to charge a golf cart battery to run a pet warming pad over my garden mount, this draws a couple of amps and at some point in the year it fails to keep up due to the double whammy of less daylight hours to charge and more dark hours to discharge it so have to take it indoors to recharge.

Dave

[Chris]

4 minutes ago, fifeskies said:

Nope

3 amps x 12 volts is 36Wh , every hour

x 3 hours is  108Wh.

 

also leisure batteries will often be rated in Ah     (amper hours)   

at 12 v , 1 Ah is the same as 12Wh.

 

Thanks I just went off to Google what exactly an Amp was again lol So Amp x Volts = Watts. In that case if we allow for 5 Amps usage at 12V for 3 hours then that would be 180 Wh. 

In that case I would need to be looking at least 100W solar panels considering summer/winter and battery reserves. 

[Chris]

15 minutes ago, Davey-T said:

Hi Chris I use a 25 watt solar panel to charge a golf cart battery to run a pet warming pad over my garden mount, this draws a couple of amps and at some point in the year it fails to keep up due to the double whammy of less daylight hours to charge and more dark hours to discharge it so have to take it indoors to recharge.

Dave

That's a good idea to run a warming blanket off solar, in my last obsy I used an electric blanket off the mains to keep the damp of my scope. I might need to factor in a warming blanket  

I can  see me ending up with a 150W solar kit!

[fifeskies]

Yes if it is 5 amps continuous then a hefty panel is needed.

But your mount will average out well below its peak current when it is slewing,

Tracking I have not measured mine but I think its under an amp.

 

You need to balance cost of a big panel against convenience , if you are running battery down a bit mid winter the odd top up in the house from a charger will refresh it for another good while of use getting its trickle charge, so a smaller panel is not that inconvenient.

 

Also batteries do leak charge over time (self discharge) , even if not being used they will lose charge slowly over time, but its not a lot compared to weekly use for astronomy.

 

[Chris]

It's expensive but maybe this 160W kit will cover everything:

https://www.photonicuniverse.com/en/catalog/full/184-160W-12V-solar-charging-kit-with-20A-controller-and-5m-cable.html?gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_EfRNwzo2XtST5KvS4-2UklVyxKt7msFH_fcEBEEjqzbwKu7P_i9DkaAgGoEALw_wcB

[fifeskies]

If you run a warming blanket continuously you will struggle to keep a battery charged , but it can be set to only kick in if its gets cold or use a timer so its only on a short while each day

 

you can get both 12 v timer and 12v temp switch that simply fit inline with the cable

[Chris]

10 minutes ago, fifeskies said:

Yes if it is 5 amps continuous then a hefty panel is needed.

But your mount will average out well below its peak current when it is slewing,

Tracking I have not measured mine but I think its under an amp.

That makes sense, I was thinking 5amps was just what medium duty mount drew, but off course this will vary depending on what the mounts doing and most of the time mounts will be just tracking sidereally which wont use much power. 

 

Edited November 15, 2020 by Lockie

[fifeskies]

2 minutes ago, Lockie said:

It's expensive but maybe this 160W kit will cover everything:

https://www.photonicuniverse.com/en/catalog/full/184-160W-12V-solar-charging-kit-with-20A-controller-and-5m-cable.html?gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_EfRNwzo2XtST5KvS4-2UklVyxKt7msFH_fcEBEEjqzbwKu7P_i9DkaAgGoEALw_wcB

That looks more like it  🤔

 

When you consider the size of panel that you see attached to eg stand alone speed warning signs , they are around this size for something that is only on now and then.

[fifeskies]

The last thing you want is for your system to shut down in the middle of the one clear night you get decent imaging conditions.

Get a decent power monitor you can use to check the battery , something on a push button so its not on wasting power all the time, though perhaps the charge controller will have a good monitor built in.

[Chris]

I guess it's better to have too much than too little, I'd better check my bank account, I might need to sell a couple of items. I've not looked at the price of leisure batteries yet lol

[fifeskies]

This should do     😜

 

[Chris]

haha I can only imagine what that's powering!? 

[fifeskies]

On a more practical note

https://cpc.farnell.com/yuasa/npc3812/battery-deep-discharge-cyclic/dp/BT00583?st=deep discharge battery

and

https://cpc.farnell.com/yuasa/npc24-12/battery-deep-discharge-cyclic/dp/BT03978?st=deep discharge battery

 

[Davey-T]

22 minutes ago, Lockie said:

I can  see me ending up with a 150W solar kit!

I've got an 80watt solar panel on my camper van and 80Ah leisure battery and can survive off grid in the summer as long as wife doesn't want to watch TV 😂

Dave

[Chris]

8 minutes ago, fifeskies said:

On a more practical note

https://cpc.farnell.com/yuasa/npc3812/battery-deep-discharge-cyclic/dp/BT00583?st=deep discharge battery

and

https://cpc.farnell.com/yuasa/npc24-12/battery-deep-discharge-cyclic/dp/BT03978?st=deep discharge battery

 

That's great thanks! The cost is ramping up a bit but I guess if I bought a 24Ah battery instead of the 38 I could always add a second battery down the line.,,,As your above image demonstrates 😄

 

Edited November 15, 2020 by Lockie

[jambouk]

Using my own solar panels at home as a baseline, I predict the 160W panel will produce on average 100-150W / day in Nov, Dec, Jan and Feb (the light-critical times). Maybe 600W / day in the summer. Heavily depends on angle tilted, azimuth direction, and any shade which will heavily hamper solar yield. Are you sure you can get the panel high enough from the ground to catch the sun on the shortest day without any shadow obstruction? You also need the panel to ideally be about 60 degrees in angle mid-winter, and how are you going to adjust and secure it in that position to stop it getting ripped off in a windy spell... You know how difficuly a wheelie bin lid is to close in a gale, and this panel is probably at least twice the surface area of the bin lid.

You say 3 amps for 3 hours once a week. I'm going to go on the pesimistic side and say 10 amps / night, and you need to be realistic that you may get a very clear spell mid-winter on consequitive nights and you want to run fo rthree nights on the trot for three hours each time, so that means with minimal charging time in the day, you are going to use 30 amps at 12v without that being replaced. I wouldn't discharge the battery more than 30% if you can help it, so if 30% is the max discharge allowed and that = 30 amps, you need a 100amp hour battery. That is portable into the house if needed. Once you get into the 200amp hour battery range, you need two people tp move it and the cost is getting steep.

You also need to factor in the efficiency of the charge controller, which I suspect is in the region of 70%-80%, and you need to factor in the fact to keep the battery in tip top condition, you will likely need to put into the battery 1.5x the power you take out.

I'd look to get mains into the observatory myself.

James

 

[fifeskies]

At a 3 amp draw a 24AH battery will last 8 hours

However that's not the full story , it will start off at 13.8v fully charged and the voltage will drop as it empties , at some point below full discharge it will fall below 12v.

This can cause issues on some mounts when they need to slew , the power LED can end up flashing with the sudden high current demand.

(which causes the voltage to dip further)

 

Should not be such an issue just tracking however.

 

10 minutes ago, jambouk said:

 

I'd look to get mains into the observatory myself.

James

 

I agree with James

Unless your observatory is really remote , the cost of getting mains installed will start to be comparable to a big stand alone system.

And no-one can bother an underground cable , a big solar panel is easy to flog if nicked.

 

Edited November 15, 2020 by fifeskies

[Chris]

16 minutes ago, jambouk said:

Using my own solar panels at home as a baseline, I predict the 160W panel will produce on average 100-150W / day in Nov, Dec, Jan and Feb (the light-critical times). Maybe 600W / day in the summer. Heavily depends on angle tilted, azimuth direction, and any shade which will heavily hamper solar yield. Are you sure you can get the panel high enough from the ground to catch the sun on the shortest day without any shadow obstruction? You also need the panel to ideally be about 60 degrees in angle mid-winter, and how are you going to adjust and secure it in that position to stop it getting ripped off in a windy spell... You know how difficuly a wheelie bin lid is to close in a gale, and this panel is probably at least twice the surface area of the bin lid.

You say 3 amps for 3 hours once a week. I'm going to go on the pesimistic side and say 10 amps / night, and you need to be realistic that you may get a very clear spell mid-winter on consequitive nights and you want to run fo rthree nights on the trot for three hours each time, so that means with minimal charging time in the day, you are going to use 30 amps at 12v without that being replaced. I wouldn't discharge the battery more than 30% if you can help it, so if 30% is the max discharge allowed and that = 30 amps, you need a 100amp hour battery. That is portable into the house if needed. Once you get into the 200amp hour battery range, you need two people tp move it and the cost is getting steep.

You also need to factor in the efficiency of the charge controller, which I suspect is in the region of 70%-80%, and you need to factor in the fact to keep the battery in tip top condition, you will likely need to put into the battery 1.5x the power you take out.

I'd look to get mains into the observatory myself.

James

 

Hi James, thanks for your input. I'm currently running the obsy of 12 D cells so just looking at an eco friendly upgrade to this. It doesn't have to be perfect and I can always charge the battery when the days get short. I concede I won't be able to have solar panels in a fully optimal 60 degree angle but I do want to keep with the eco theme beacause I think it would be a cool thing to do and my obsy is mainly made from recycled and salvaged materials so keeping in with that theme.

Maybe wind power would be better? or a combination of both wind and solar? Yes mains would be easier of course or I can keep on running the obsy of my 12 D cells and just add a recahrgeable battery pack for a little LED light.

[Chris]

19 minutes ago, fifeskies said:

it will start off at 13.8v fully charged and the voltage will drop as it empties , at some point below full discharge it will fall below 12v.

I should probably put more of the money into a battery with a large Ah capacity in this case. I've had mounts with flashing LED power issues in the past and the mounts tend to not function properly in this situation, they can go a bit bonkers 😜

[Chris]

I could forget the solar altogether and just get a battery I can just about carry into the house to charge every now and again. I just thought solar would decrease the freguency of this which would be handy, and it would be eco friendly. I might have a a quick look at wind turbines as well...you never know

Edited November 15, 2020 by Lockie

[fifeskies]

 

 

2 minutes ago, Lockie said:

battery with a large Ah capacity

Yes , its best to go big from the start.

With 2 batteries on 12 v they need parallel connection which is not ideal unless there is an A/B switch (like in some motorhomes) so adding a 2nd later is not as easy as it seems.