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RTLR 12
Post Laureate

Reged: 12/04/08

Loc: Capistrano Beach, Ca
Re: What size generator is needed? [Re: dan_h]
#5291300 - 06/27/12 09:53 AM

Thank, Dan. That answers a lot of questions. I take a look with your recommendations.

Stan

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Phil Sherman
Pooh-Bah

Reged: 12/07/10

Loc: Cleveland, Ohio
Re: What size generator is needed? [Re: RTLR 12]
#5291309 - 06/27/12 10:00 AM

The issue you haven't addressed is how much power you'll consume for each night's observing. You have 62*12 or just under 650W of power available. Assume that it's warm (no cold effects to decrease battery performance), and that you can actually use 80% of the battery's rated capacity. This gives you 470W of power available.

If you're visually observing, the only thing you need to power is the mount. Assume an average current draw of 1.5A/hour, round up and you'll need 20W/hour. Your existing battery should last for 470/20 or 23.5 hours. You'll only have 6 hours observing time a night at this time of year so a single charge on the batteries should last for almost four night's use

If you're imaging, the power equation changes drastically. The most common mistake made is to get a small 110V cigarette lighter inverter to power the computer. This means converting 12V dc to 110V ac then back to 18-20V dc to run the computer. Two voltage conversions, each with its own power losses is the quickest way to drain a battery. A better approach is to get a 12V power supply for the computer. A single voltage conversion will cut conversion losses by 50%. Examine your laptop's battery with a magnifying glass. The battery's capacity will be part of the information printed on the label. An 85W battery that (supposedly) runs the laptop for four hours means that the average power use is just over 20W/hour. All equipment running on voltages between 5V and 12V should be powered from DC-DC switching regulators. One of these nifty devices will give you 2.5A at 5V while drawing less than 15W from your 12V battery. Two USB powered imaging cameras and a hub will require less than 10W/hour from the battery.

If you're running a full imaging setup, with computer, you could need the following power from the battery every hour:
18W mount
07W guide camera
25W imaging camera with cooling
25W computer

This totals 75W/hour which means that the battery should last for 470/75 or just over 6 hours. Gel cell batteries are usually rated when used at the 10 hour rate, which you've exceeded. Capacity, in this case, should be downrated somewhat, so you'll probably get around 5.5 hours of battery life. Dew heaters, while easy to run off of 110AC power in an observatory, usually require large (heavy) deep cycle lead acid batteries for field use.

To recharge the batteries, you need to figure on inputting 120% of the power drawn from them. If you use 500W of power at night, you'll need 600W of power to recharge the battery. If you figure on 12 hours a day of sunlight, you'll need 50W of power/hour from solar panels for the imaging setup but only 10W for visual observing. Solar recharging can be handled for a visual observer using readily available solar chargers from Harbor Freight Tools. Don't forget that a solar panel only generates its rated output when directly facing the sun. A fixed panel's average output will be less than its rated output.

Another possibility for recharging your batteries is to use the charger you'll be bringing with you, your transportation. A set of jumper cables and an hour or two connected to your vehicle should easily recharge your battery. Even at 2 gallons/hour, a very high gas usage rate at idle, a two hour charge run will cost less than \$15 (this week). Compare this cost to \$320 for a generator and a couple of 5 gallon gas cans and it may be a cost effective option.

Phil

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RTLR 12
Post Laureate

Reged: 12/04/08

Loc: Capistrano Beach, Ca
Re: What size generator is needed? [Re: Phil Sherman]
#5291349 - 06/27/12 10:31 AM

Phil,

Very well thought out. I really think your numbers are very close. I have 6 dedicated jump packs to run my equipment. Right now my Honda generator is my '08 Accord. I spend 7 to 14 day at a time in the field and have used quite a bit of fuel in my 'Honda Generator'. If i'm going to spend \$1000+ on recharging my power supplies the decision is which way to go...Gas or solar? Thanks to your numbers I know what is required to maintain the power.

Stan

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Jeff Struve
sage

Reged: 11/05/10

Loc: Iowa, USA
Re: What size generator is needed? [Re: RTLR 12]
#5291380 - 06/27/12 10:59 AM

Lots of great input here... I noticed that although I responded via my smart phone I was out smarted because not of my replies went on the site... so ...

I thought about charging off of the car, but don't want to risk any car problems... and there are towns/camp site/s where I could probably charge up, but don't want to risk not finding a place available or be a hog and tie up a station for long periods of time or want to leave my gear unattended for long periods of time... I am weighing spending another \$250 to double my gel cell capabilities, but think that maybe it would be more versatile to have a generator around the house...

For my useage... and this was asked a couple of times... I should know but I don't... but yes, I plan on imaging, and was thinking that depending on if I need dew zappers and how I run my laptop, I hope to get 4-8 hours out of my 62amphr supply... I will be running an SBIG ST8300c for the imager, the SBIG STi-c for the guide, the Atlas mount with GPS, a RigelSys electronic focus, Kendrick dew control, and a 14" Win7 64 bit i7 laptop, and a 6 port powerd hub...

I am hoping to secure a spot at Cedar Bay where there is power... but they don't take reservations...

Powering all of my gear via DC... I am not using any 12vDC to 120vAC converters the only thing is the laptop where I purchased a 12v to 19v converter...

I like the solar panel idea, but thinking that living in the midwest with rain storms and power outages, a generator may not be a terrible thing to own..

so... with a fairly spent 62amphr gel cell... will the Honda 1000 be very workable? How long does it run on a full tank of gas... how large is the gas tank?

Thanx!

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RTLR 12
Post Laureate

Reged: 12/04/08

Loc: Capistrano Beach, Ca
Re: What size generator is needed? [Re: Jeff Struve]
#5291393 - 06/27/12 11:10 AM

3.8hrs(full load) to 8.3hrs(¼ load). The fuel tank is .6 gal.
I just looked it up.
Stan

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Lorence
professor emeritus

Reged: 09/15/08

Re: What size generator is needed? [Re: Jeff Struve]
#5291600 - 06/27/12 01:23 PM

Quote:

Thanx... I"ll check into the Hondas,,, the one I am looking at is a generic brand.... 3200 watt... noise is less than 70db, so it seems quiet... runs 10hrs on a tank of gas at half power... I'll need to check the max input on the charger tomorrow... but how does that number correspond to what the generator does/has?

70 db is more than loud enough to bother some. At any rate the specs on generic equipment is little more than marketing hype.

One of the major drawbacks of the generic brands is lack of service and or parts. There are probably millions of small generic gas powered generators, chain saws, mowers and the like in landfills because they can't be repaired. Once the warranty is up the failure of \$2.00 part is a trip to the junkyard.

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dan_h
Carpal Tunnel

Reged: 12/10/07

Re: What size generator is needed? [Re: Jeff Struve]
#5291735 - 06/27/12 03:09 PM

Quote:

so... with a fairly spent 62amphr gel cell... will the Honda 1000 be very workable?

Thanx!

A 1000watt generator will charge your batteries and many, many more. The generator provides 20 times as much power as a good 50watt solar charger. Since you can only push juice into the gel cells at a fixed rate, you will probably have enough power left over to run a coffee pot at the same time (and that is reason enough to have the generator.)

dan

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Jeff Struve
sage

Reged: 11/05/10

Loc: Iowa, USA
Re: What size generator is needed? [Re: dan_h]
#5291747 - 06/27/12 03:21 PM

Coffee is the selling point here... I am waiting for a guy on Craigs list to respond to my inquiry on the Honda 1000 he has for sale here locally... he's asking \$475...

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RogerRZ
Whatta you lookin' at?

Reged: 01/09/06

Loc: West Collette, NB, Canada
Re: What size generator is needed? [Re: Lorence]
#5291749 - 06/27/12 03:22 PM

Quote:

Quote:

Thanx... I"ll check into the Hondas,,, the one I am looking at is a generic brand.... 3200 watt... noise is less than 70db, so it seems quiet... runs 10hrs on a tank of gas at half power... I'll need to check the max input on the charger tomorrow... but how does that number correspond to what the generator does/has?

70 db is more than loud enough to bother some. At any rate the specs on generic equipment is little more than marketing hype.

This is true. I have a Yamaha 2600 that specs 60dba, and I wouldn't want it running anywhere near me in a campground for any length of time, and I don't imagine the neighbors would like it either .

I would go for a 1000 watt inverter model from either Honda or Yamaha, and a 2000 watt model if you can swing the extra \$4-500. Cry once, get a good one...

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dan_h
Carpal Tunnel

Reged: 12/10/07

Re: What size generator is needed? [Re: Jeff Struve]
#5291888 - 06/27/12 05:09 PM

Quote:

Coffee is the selling point here... I am waiting for a guy on Craigs list to respond to my inquiry on the Honda 1000 he has for sale here locally... he's asking \$475...

Be careful here. A lot of coffee pots will easily exceed the 1000watts. For example, a Keurig home brew is 1600watts. Even a simple electric kettle is 1500watts.

A 1000watts is ample for many applications but small appliances can really chew up the power.

dan

dan

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JMW
scholastic sledgehammer

Reged: 02/11/07

Re: What size generator is needed? [Re: dan_h]
#5292517 - 06/27/12 11:48 PM

I have been going to star parties the last 4 years with solar on the roof of my 5x8 cargo trailer. I have 240 watts of solar feeding 220 amp-hours of batteries. I use the SunSaver 15 MPPT controller and it will put 15 amps back into my batteries under full sun. You can buy the larger 230 watt panels for about \$1.10 a watt now days. I use the solar to power my DC freezer, laptop, mount, fans and lights. The batteries last longer because they never get discharged more than one night since the solar is always available the next day.

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Paul Romero
scholastic sledgehammer

Reged: 04/05/05

Loc: Reno, NV
Re: What size generator is needed? [Re: core]
#5292584 - 06/28/12 12:53 AM

Quote:

I presume prices for a new Honda EU1000/2000i are pretty much 'fixed'? Anyone has a recommendation as to where would be a good place to purchase a unit? I've also been looking at the Yamaha EF2000iS as an alternative, any opinions?

I would recommend the Yamaha you suggested, as it has a built in battery charger. Your locally owned RV shop is a good place to go for purchase. The cool thing about the 2000 watt units is that you can combine two for those times you need to power an A/C in your trailer or motorhome, but then still have the freedom to use one of these very small/quiet units to power your gear should you ever sell the RV.

good luck with your purchase,

Paul

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Jeff Struve
sage

Reged: 11/05/10

Loc: Iowa, USA
Re: What size generator is needed? [Re: Paul Romero]
#5292777 - 06/28/12 07:20 AM

Well... back to the drawing board... the Craigs List one is sold... guess I'll have to bite the bullet and try an RV store...

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RTLR 12
Post Laureate

Reged: 12/04/08

Loc: Capistrano Beach, Ca
Re: What size generator is needed? [Re: JMW]
#5292849 - 06/28/12 08:50 AM

Quote:

I have been going to star parties the last 4 years with solar on the roof of my 5x8 cargo trailer. I have 240 watts of solar feeding 220 amp-hours of batteries. I use the SunSaver 15 MPPT controller and it will put 15 amps back into my batteries under full sun. You can buy the larger 230 watt panels for about \$1.10 a watt now days. I use the solar to power my DC freezer, laptop, mount, fans and lights. The batteries last longer because they never get discharged more than one night since the solar is always available the next day.

Jeff,

That sounds really great. Sure is enough power for almost any need. Do you think there is a way to attach it to the roof of my tent?

Stan

I have been looking at this little number though...

http://www.batterystuff.com/solar-chargers/P362watt.html

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Phil Sherman
Pooh-Bah

Reged: 12/07/10

Loc: Cleveland, Ohio
Re: What size generator is needed? [Re: RTLR 12]
#5293008 - 06/28/12 11:10 AM

One thing to watch out for with small generators is that some of them use 2 cycle engines requiring a gas/oil mixture. If I was looking for one of these; I'd spend a few more \$ and get one that uses straight gasoline. I saw the Hondas in use earlier this year when I attended the RV show in Quartzite, AZ and was very impressed with how quiet they are.

When using a generator to recharge batteries using a smart charger, you'll need to remember that the charger doesn't charge the batteries at a high rate for most of the charge cycle. My 2/10/15A charger would probably take 6-8 hours or more to recharge a 62AH battery. The Honda's "save gas" mode will help out here. Another possibility is to get a couple of chargers and provide a charging station for others.

Phil

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Jeff Struve
sage

Reged: 11/05/10

Loc: Iowa, USA
Re: What size generator is needed? [Re: RTLR 12]
#5293064 - 06/28/12 11:45 AM

I guess to mount the pannels on a tent you could ue them as the floor... but then you'd have to have clear walls...

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Jeff Struve
sage

Reged: 11/05/10

Loc: Iowa, USA
Re: What size generator is needed? [Re: Phil Sherman]
#5293073 - 06/28/12 11:50 AM

Not a bad idea on having an extra charger to have available for other users...

I am seeing EU200i on eBay for the \$800 - \$1000 range... I kinda dread spending that much on a generator, especially if I am paying for decibel levels... seems that even the Honda would be disruptive out on the observing field... so is volume important in a campsite if it is just run during daylight hours?

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imjeffp
Aluminum Falcon

Reged: 09/30/03

Loc: Cedar Park, Texas
Re: What size generator is needed? [Re: Jeff Struve]
#5293120 - 06/28/12 12:16 PM

Quote:

Not a bad idea on having an extra charger to have available for other users...

Maybe have a tip jar set out? Little portable electric meters?

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RogerRZ
Whatta you lookin' at?

Reged: 01/09/06

Loc: West Collette, NB, Canada
Re: What size generator is needed? [Re: Jeff Struve]
#5293200 - 06/28/12 12:58 PM

Quote:

Not a bad idea on having an extra charger to have available for other users...

I am seeing EU200i on eBay for the \$800 - \$1000 range... I kinda dread spending that much on a generator, especially if I am paying for decibel levels... seems that even the Honda would be disruptive out on the observing field... so is volume important in a campsite if it is just run during daylight hours?

You're not just paying for decibels. You're also buying dealer/parts support well into the future, along with proven reliability. This is also a reason to buy at your local shop vs. Ebay. Come service time, guess who will get their generator looked at first (hint--it won't be the ebay guy).

As far as daytime volume at a campground, I would say there's never a good time to be making excessive noise. Your neighbors will thank you...

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starrancher
Carpal Tunnel

Reged: 06/09/09

Loc: Northern Arizona
Re: What size generator is needed? [Re: RTLR 12]
#5293248 - 06/28/12 01:24 PM

Quote:

Quote:

I have been going to star parties the last 4 years with solar on the roof of my 5x8 cargo trailer. I have 240 watts of solar feeding 220 amp-hours of batteries. I use the SunSaver 15 MPPT controller and it will put 15 amps back into my batteries under full sun. You can buy the larger 230 watt panels for about \$1.10 a watt now days. I use the solar to power my DC freezer, laptop, mount, fans and lights. The batteries last longer because they never get discharged more than one night since the solar is always available the next day.

Jeff,

That sounds really great. Sure is enough power for almost any need. Do you think there is a way to attach it to the roof of my tent?

Stan

I have been looking at this little number though...

http://www.batterystuff.com/solar-chargers/P362watt.html

Wow ! They are very proud of that unit ! Almost a grand for that set up ?
Pretty steep I'd say .

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