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Running the CPC off my car battery

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#1 Bruce N

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Posted 26 July 2013 - 10:18 PM

How long can I run my cpc 800 off my car battery from the cigarette lighter jack without draining the battery?

#2 Stacy

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Posted 26 July 2013 - 10:31 PM

How long can I run my cpc 800 off my car battery from the cigarette lighter jack without draining the battery?


Hi Bruce.

The answer to that question depends on the type and condition of your car battery. However, you should be able to use your scope for a few nights without any problems. Always smart to charge between sessions if possible. Why do you ask?

Stacy

#3 Digital Don

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Posted 26 July 2013 - 11:53 PM

How long can I run my cpc 800 off my car battery from the cigarette lighter jack without draining the battery?


Even though Stacy's answer may be accurate, I think the real question you should ask is "How will get home if I can't start my car?"

If you observe with friends who could jump start your car in an emergency, no problem. If you observe alone, it's really not prudent to run a telescope and it's ancillary equipment from your car battery.

You might consider buying a 'jump start battery' to run the scope. They are relatively inexpensive, rechargeable, and can power a scope and anti-dew equipment for a number of hours.

Don:usa:

#4 Bruce N

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Posted 27 July 2013 - 12:04 AM

Yes, that is the question. I've just not wanted to spend the $50 bucks to buy a jump start battery. But thanks. I'll buy one tomorrow.

#5 rigelsys

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Posted 27 July 2013 - 11:57 PM

$38 at harbor freight

http://www.harborfre...38391.html?c...

plus you might be able to get another 20% off

#6 David Knisely

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Posted 28 July 2013 - 12:21 AM

It would work OK if it was a brief one-time deal, but there is a problem with doing this long-term. Car starter batteries are intended to provide a brief high-current burst of electricity for the starter motor, and not to provide a constant low-current output (although they are quite capable of doing this occasionally). Their plates tend to be rather thin, and under a low constant current draw, the plates can have their lead flake off. This can (if carried on long and frequently enough) eventually damage the plates and reduce or kill off the battery's ability to provide that big burst of power needed to start the car, potentially leaving you stranded. This is one reason why it is recommended that some external battery system (preferably deep-cycle batteries) be used for powering scopes and other electronic hardware in the field. Clear skies to you.

#7 Stacy

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Posted 28 July 2013 - 01:34 AM

It would work OK if it was a brief one-time deal, but there is a problem with doing this long-term. Car starter batteries are intended to provide a brief high-current burst of electricity for the starter motor, and not to provide a constant low-current output (although they are quite capable of doing this occasionally). Their plates tend to be rather thin, and under a low constant current draw, the plates can have their lead flake off. This can (if carried on long and frequently enough) eventually damage the plates and reduce or kill off the battery's ability to provide that big burst of power needed to start the car, potentially leaving you stranded. This is one reason why it is recommended that some external battery system (preferably deep-cycle batteries) be used for powering scopes and other electronic hardware in the field. Clear skies to you.


I have been using a jump start / power supply / air compressor type battery from Costco. It seems it's capacity is far more than the "power tanks" I own from Celestron and others. I wonder what type of batteries are in those?

I know what you mean about auto batteries . I have 4 6-volt golf cart battteries (also from Costco) wired in series and parallel to provide 12v DC power for my rv. I know they are designed to provide a continous power supply and be able to discharge up to 50% or so on a regular basis.

Stacy

#8 David Knisely

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Posted 28 July 2013 - 03:28 AM

It would work OK if it was a brief one-time deal, but there is a problem with doing this long-term. Car starter batteries are intended to provide a brief high-current burst of electricity for the starter motor, and not to provide a constant low-current output (although they are quite capable of doing this occasionally). Their plates tend to be rather thin, and under a low constant current draw, the plates can have their lead flake off. This can (if carried on long and frequently enough) eventually damage the plates and reduce or kill off the battery's ability to provide that big burst of power needed to start the car, potentially leaving you stranded. This is one reason why it is recommended that some external battery system (preferably deep-cycle batteries) be used for powering scopes and other electronic hardware in the field. Clear skies to you.


I have been using a jump start / power supply / air compressor type battery from Costco. It seems it's capacity is far more than the "power tanks" I own from Celestron and others. I wonder what type of batteries are in those?

I know what you mean about auto batteries . I have 4 6-volt golf cart battteries (also from Costco) wired in series and parallel to provide 12v DC power for my rv. I know they are designed to provide a continous power supply and be able to discharge up to 50% or so on a regular basis.

Stacy


Some are standard lead-acid (often sealed) while other are AGM (absorbed glass mat). However, most tend to be more in the "starter" style of battery rather than deep-cycle. Clear skies to you.

#9 cn register 5

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Posted 28 July 2013 - 05:11 AM

I think the predictions of doom running a mount off a car battery are a little over done.

The CPC on it's own takes about 0.5A when tracking, that's 6W, about the same as one interior light.

I don't think that will kill a car battery in a night unless the battery is already on it's last legs. But if you add all the extra paraphernalia - dew heaters, CCD cameras, laptops in particular - then that's more of a problem.

I ran a NS11GPS and a laptop through an inverter off the car battery for the duration of the transit of Mercury a few years ago and it wasn't a problem.

More of a problem will be tripping over the long trailing lead, that's a good reason to get a power supply that can be hidden under the tripod.

Chris

#10 Stacy

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Posted 28 July 2013 - 05:16 PM

I think the predictions of doom running a mount off a car battery are a little over done.


Uh huh, sure. And just how do we know you are not the monster? :ubetcha:

#11 cn register 5

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Posted 29 July 2013 - 03:42 PM

Do you have something rational to contribute, or are you just being rude?

#12 brianb11213

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Posted 29 July 2013 - 04:02 PM

The CPC on it's own takes about 0.5A when tracking

Maybe yours does. My CPC1100 draws 2.5A at 12V (substantially more when slewing). Add 3.5A for a dew control strap at the objective and 1A for a dew control strap for the eyepiece for a total draw of around 7A. This is entirely consistent with my 70AH deep cycle battery not lasting a whole night except during the short, warm nights of summer.

#13 cn register 5

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Posted 29 July 2013 - 04:59 PM

2.5A at 12V is 30W. That's enough for something to be getting hot. Have you measured it? With a meter? My measurements of scope power use are far less than this.

4.5A for heaters? Seriously? Are you not concerned about the scope catching fire?

I did exclude dew heaters, Laptops, Coffee makers, aircon and so on, just the scope.

Chris

#14 Stacy

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Posted 29 July 2013 - 06:22 PM

It's much safer to get a dedicated battery. I have actually used my scope battery to start the rv once or twice when I let the starter battery go dead after a week in the woods.

That's when the monster strikes! When your car won't start!!! (Sorry, thought everybody knew that)

#15 David Knisely

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Posted 30 July 2013 - 03:49 PM

cn register5 wrote:

I think the predictions of doom running a mount off a car battery are a little over done.


I was not predicting any "doom", but only providing a reason why it is not an outstanding idea to use the vehicle's starting battery for long-term low current draw use. I too have occasionally used my vehicle's battery to power my NexStar 9.25GPS for a couple of hours (current drain between 0.5 and one amp except during slewing), but this is only when there is no other option. I have two other portable battery systems which I normally use for the telescope and my laptop because I don't want to stress the van's battery too much. One problem many vehicle owners have is that they do not pay enough attention to the age or maintenance of their vehicle batteries. In those cases, long term use of a low-current application can shorten vehicle battery life or potentially kill off enough of that high current capacity to make that battery unable to power the vehicle's starter motor properly. This can be a real problem under cold winter observing conditions as battery capacity is already reduced by the temperature. While it might be unlikely that the use of the vehicle's battery to power a single scope will completely kill the battery, it is at least somewhat possible that an inattentive observer who neglected to keep their vehicle battery up to snuff might end up stuck out in the middle of nowhere unable to start their vehicle even though that battery was moments before happily powering their telescope. This is what I am cautioning against. Clear skies to you.

#16 rigelsys

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Posted 30 July 2013 - 04:59 PM

CPC is spec'd at 12 VDC-1.5A (Tip positive)

Celestron's recommended AC-DC wall wart is 2.5A

My experiences is with age and cold and lubrication stiffening, 2x that is required to keep the voltage up so the computer doesn't reset when slewing.

And it makes a dandy hand warmer ;)

#17 cn register 5

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Posted 30 July 2013 - 05:36 PM

This is a load of FUD. Have you actually measured the current drain?

The reason for the high peak current specification is obvious to anyone who understands how DC motors operate and has nothing to do with the average current. The average current is what matters for battery life.

Still, It won't wreck the mount. Carrying vast amounts of unnecessary batteries around won't do any harm, other than to your bank balance and your back.

You don't have to believe me. You can measure the current. Meters are easily available for a few pounds and you can measure what current your scope takes.

Astronomy is supposed to be a science, why not do some?

Chris

#18 RTLR 12

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Posted 30 July 2013 - 05:49 PM

Astronomy is supposed to be a science, why not do some?


Anyone ever try to run their mount on potato batteries? :scratchhead:

Stan

#19 rboe

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Posted 30 July 2013 - 10:45 PM

I've run my NS11 several times with my car battery. Switched to the Starizona battery pack; which will not last a Messier Marathon. Almost though.

I have since started using a Lithium Ion Fe battery I bought for a motorcycle. I've only used it for a few hours at a time so I have never come close to tapping it out. Expensive but seems to have gobs more power than the Starizona.

#20 rigelsys

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Posted 31 July 2013 - 06:47 PM

This is a load of FUD. Have you actually measured the current drain?

The reason for the high peak current specification is obvious to anyone who understands how DC motors operate and has nothing to do with the average current. The average current is what matters for battery life.

Still, It won't wreck the mount. Carrying vast amounts of unnecessary batteries around won't do any harm, other than to your bank balance and your back.

You don't have to believe me. You can measure the current. Meters are easily available for a few pounds and you can measure what current your scope takes.

Astronomy is supposed to be a science, why not do some?

Chris


Fact not FUD. Stepper motors are not DC motors. Stepper pulse currents are as high as 1A, depending upon load.

I've had to upgrade the AC/DC power supplies on a fleet of 10x 8" nexstars over the last 10 years due to lubrication stiffening causing current draw to gradually increase with age which causes handsets to crash (pulling down the voltage). You know, actual experimentation in the field, not arm chair science... tho you might try Ohms law. V=IR... assume V = 12V, look up R for typical stepper specs, solve for I... Higher current, more torque. Am in the habit of running steppers at currents that make them nice tea warmers.

#21 mclewis1

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Posted 01 August 2013 - 12:58 AM

All true but for the small issue that all Nexstar controlled scopes/mounts use servo and not stepper motors (your comments could easily lead someone to believe the opposite). There are indeed differences between servo and stepper motors in the way they draw current when loaded down but it's probably not enough to make a difference in this discussion.

The point about scopes/mounts requiring a bit more current as they age is often true. Gears loosen up a bit with age but the lubrication does dry out and pick up dirt which causes things to tighten up. With the scopes I've been around over the past 10 years I've never seen that situation really make a big impact on the power requirements ... at least not enough to cause real obvious problems.

Nexstar hand controllers are usually fine with voltages down to around 10.5v or so. Below that and they will start to do strange things (slew to widely incorrect positions for example). Batteries usually have to be depleted well below 50% to end up with voltages below 10.5v.

AC 12v power supplies rated at 2.5amps should normally be fine for CPCs, even old ones. Celestron used to supply a 1.5amp power supply for the NexStar GPS scopes, but this often caused problems. The power supply also wasn't of very good quality and the scopes would draw enough current to cause those older power supplies to consistently run hot, which really shortened their lifespans.

The bigger electrical issue though is usually the physical connection of the power plug/socket. That problem tends to show up as a reset of the hand controller rather than just strange operations.

#22 Gastrol

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Posted 01 August 2013 - 04:56 PM

Would a 35AH golf cart or wheel chair battery be a good choice for running the CPC for several hours? I'm thinking of picking one up at Harbor Freight.
I don't take my CPC out in the field that often and I didn't want to spend $100 on a marine/deep cycle battery.

#23 David Knisely

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Posted 01 August 2013 - 06:41 PM

Would a 35AH golf cart or wheel chair battery be a good choice for running the CPC for several hours? I'm thinking of picking one up at Harbor Freight.
I don't take my CPC out in the field that often and I didn't want to spend $100 on a marine/deep cycle battery.


These batteries (golf cart and motorized wheelchair batteries) tend to be deep-cycle, so they should work for running your scope if their voltage is right. A 35 amp-hr battery fully-charged should run your CPC scope easily for at least a full night if not a couple of nights if the battery is in decent condition. Clear skies to you.






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