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Powering your mount with Pre-charged AAs.

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#1 Eddgie

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Posted 24 August 2013 - 01:58 PM

Many people recommend car emergency batteries or small 12 volt lead acid batteries for running a telescope.

Often, these devices have very limited capacity, are somewhat expensive, and often have a short life (I have had two different 12 Volt emergency kind of packs and neither lasted more than 2 years).

Here is a great alternative.

You can buy pre-charged AA batteries these days that have a minimum 1900 milliamp rating, will last a year without loosing more than about 15% of their charge, and can be recharged 1500 times. (Not a typo. These batteries are seriously good).

You can get them here, and you need 8 for most mounts. This will only give you 11.2 Vdc, but all handsets I have tried work at 11.2 volts.

Here are specifically the batteries I recommend:

Eneloop 2000 3rd Gen pre-charged.. State of the art....

Next, you need an 8 battery holder. $1.78 from Parts Express

Battery holder

Now, you need a 9 volt type clip, also from PE for about $.44:

9 Volt type clip

And I would recommend a right angle type cable. I hate the standard 5.5mm power plugs because the cables stick out so far. You are always hitting them which causes the contacts in the plug to deform, and makes an intermittent connection. I hate that Celestron and everyone else has not gone right angle. I always had problems with the CGE because the handset cord would drag across the power jack causing intermittent power drops. Dang, I hate that, don't you? Problem is greatly diminished with right angle plug.

Here is the solution and you can get it in 5.5mm 2.1 or 2.5 for either Meade or Celestron as you may require...

5.5mm 6 ft cord

Now, last thing you need is a battery charger (Ok, but not the best solution) or a more expensive battery conditioner/charger. These sell for about $50 (vs the basic charger which is only $20) but if you love the cost savings of pre-charged batteries, you will want to buy more batteries, and these more expensive chargers really let you take great care of your batteries.

Here is the charger I use. There are less expensive versions of "Advanced" charger, but this is one of the best deals you will find on a very advanced high capacity charger:

Advanced charger

Now you just solder the leads to the 9 volt clip (observing tip polarity).

In your hand you now have 15 amp hours of capacity. This is the amazing thing about these batteries as compared to sealed 12 volt batteries. The energy storage density is far higher, making this supply so compact that it can be tucked in anywhere. Hung on a spreader with a clip, velcroed to the ground board.

No more cables or wires on the ground!!!

This will likely run most modern Go-To telescopes for hours.

When you are done, you can simply unclip the pack from the cable and you are done with fussing with the prongs on your power cable because you are never removing it... Tape it or secure it to the mount.

Yes, it is a bit more hassle to pop the batteries and re-charge them, but it takes only a minute to pop the batteries, and while you will have to make two runs on the charger to charge all eight, well, it isn't like you have to sit there and watch them.

If you take the cost saver route, you can get this put together for under $50.

But Eneloop technology is prime time stuff, and once you start using these batteries, you will find yourself buying more and never using a disposable AA or AAA again. They are that good. Expensive, but that good.

And the parts for the cable/holder are so inexpensive that you can build yourself a backup and provision it with throw away AA Alkalines if you want.

Anyway, after you charge the batteries, you can put them back into the 8 cell holder and stick them back on your mount so you are ready for the next couple of nights of observing. Just snap on the 9 volt connector and you are ready to rock. The pack itself is so small and light that you can dangle it on a lanyard or Velcro on the bottom of the holder to a patch on the base of your Go-to dob.

Just thought I would bring this up as an alternative to using heavy throw away batteries.

And Amazon has a "Basic" pre-chargable that is about $5 cheaper for 8, and they do speck out on my charger at the same capacity as the Eneloop, but the eneloop has slower discharge on the shelf and is good for 500 more charges.

Hope some of you find this helpful...

#2 Ira

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Posted 24 August 2013 - 07:46 PM

Good idea. I have started going the route of using rechargeable batteries wherever I can. I go through aaa's at a furious rate. Not only does it get expensive but it's an ecological disaster.

/Ira

#3 Eddgie

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Posted 24 August 2013 - 08:02 PM

Well, I am using almost all pre-charged now, and the Eneloops are fantastic.

I have had Sanyo ni-cads in the past and these were by far the best ni-cads I had used.. Mine lasted maybe 7 years.

I think these Eneloops are good for 10 years though. It is about the best rechargeable you can buy I believe.

I do though think that the investment in a good charger/conditioner is worth it.

Here is an outstanding model:

Great charger/conditioner

The main advantage of these kinds of chargers is that they will tell you how much capacity a battery has when fully charged (they do a discharge cycle and a full charge).

Then, when you re-charge, they tell you how much current was added to top off the battery.

That way, if you know the battery had 2000 milliamp capacity (which is about what the Eneloops run) and you put 500 milliamps back in to top it off, you know that you still had 1500 MA of capacity left.

This way, if you run your mount one night for two hours and you use X amount of current, you can calculate how many total hours the mount would run.

This way you can estimate how many nights you can make it go.

I an not so anal that I check every battery every time, but I like knowing how long my mouse will run, or my telescope will run on a charge so I know about how often to change them.

#4 ohata0

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Posted 24 August 2013 - 10:42 PM

question...how are you calculating the Vdc? are you just measuring it? because doesn't the output on the battery say 1.2 V? So shouldn't it be closer to 9.6 (1.2x8)?

That does seem like a nice idea, since i do have a lot of eneloops, and would rather buy more of those than buy a powertank or deep cell battery or something.

definitely something to consider when i want to go mobile.

#5 Eddgie

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Posted 25 August 2013 - 08:34 AM

Well, if you are concerned, you could get closer by using a 10 AA Battery holder and just using a dummy battery in one position or just soldering a jumper across..


10 AA Battery Holder for $6.00

The pre-charged batteries I am using meaure measure 1.35vdc each, so voltage is a bit less than 11 vdc.

But remember, these batteries will run closer to rated voltage long after most other batteries are dropping off in voltage.

Also most telecopes do not actually run at 12 vdc (though the motors run at rated voltage). The electonics in most of these devices use a lower voltage and that voltage is regulated by the handset. The motors might run a bit slower, but they will run fine.

When using a heavy load, my DC power supply was offen dropping to 10 volts (dew heater, high speed slew) and I never had any problem.

But yes, operational voltage will be right at 10.8 volts to 11.2 volts (some pre-charged batteries run at about 1.38 volts).

The Eneloops though measure out at 1.34 to 1.36 and deliever rated voltage to well under 40% charge.

Anyway, the motors may run a bit slower, but only a bit, and the electronics are all using a regulated voltage that is considerably less than 12 vdc. Virtually no IC solid state electronics today run off of native 12 volt sources and are almost always regulated down.

Not saying that this will work for every scope model. I don't know if that is the case.

But it works.

And if there is a concern, just bump up to a 10 battery holder and either run all 10 (no more voltage than a running automobile) or nine and a dummy.

And with all 10 batteries, you would have a freaking 20 amp hour supply. This would run a telescope and even a dew heater for several hours.

These batteries are pretty amazing. No other battery I have tested is nearly as good as this AA.

#6 cn register 5

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Posted 25 August 2013 - 09:46 AM

And with all 10 batteries, you would have a freaking 20 amp hour supply. This would run a telescope and even a dew heater for several hours.

The 10 cell pack is still 2 Amp hour, the difference is that it's 2 Amp Hours at 12V, not 2 Ah at 1.2V

So if your scope takes 0.5 A on average the pack will run it for 4 hrs - in theory. If your dewheater takes 1A at the normal 12V then it will run for 2 hrs.

All these numbers are theoretical of course.

Chris

#7 sg6

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Posted 25 August 2013 - 10:29 AM

Still only 1.2volt not 1.5volt. Most goto's really dislike a low voltage and give odd results.

Something like the Tracer 12V Li polymer pack is a better option. Come in 8Ah and 10Ah and will sit on a goto base easily.

#8 Eddgie

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Posted 25 August 2013 - 12:38 PM

The Eneloops are 1.35 volts as measured with a varience of about +/- .01 volt as I have measured them.

Each battery has 2000 milliamp capacity.

The total capacity for a 10 battery pack then would be 20 amp hours at 13.4 volts. This will run a Go-To telescope with moderate amount of Go-To for several sessions.

Even the 10.8 volt pack will run a CG4 ASGT easily for a session.

Slews are slightly slower, but not enough to make a big difference.

I really don't care what people use. Just mentioned these as an option. Try it or don't try it as you see fit.

I like the solution far better than using a lead acid battery because in the long run it is a lot cheaper. Discount lead acid batteries only seem to last for a couple of years.

Also, lead acid does not tolerate cold as well. The Eneloops will deliver down to about -20 Centigrade....

Only trying to present an option. Everyone is free to try it or not. I like it as a solution, but maybe no one else does and that is A-OK for me....

#9 cn register 5

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Posted 25 August 2013 - 05:00 PM

If you connected 10 batteries in parallel you would get 1.35V and 20Ah but connected in series you get 13.5V and 2 Ah.

I'm not saying this is a bad option, I think it's a good one for short sessions of a few hours. You aren't going to get more than about 4 hours of scope use.

Chris

#10 Eddgie

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Posted 25 August 2013 - 07:19 PM

They are connected in series. Connected in series, you get 13.4 volts with 20 amps of capacity.

My scopes draw less than 2 amps when slewing with both motors, and about .7 amps when tracking for the GEMS and about 1.1 amps when tracking with the Dob.

Since most of the time the scope is used it is tracking and not slewing, a 14 amp pack will run the scope for several hours unless you are doing a lot of slewing, but even slewing a lot, you should get an evening out of it.

I know people that run scopes on 7 amp and 12 amp sealed batteries, and many of the Power Tank type devices only have about this much capacity.

No one has to do this if they don't want. I just thought people would be interested.

#11 wolfman_4_ever

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Posted 25 August 2013 - 08:55 PM

Good post. I use eneloop batteries and equivalent in all my electronic components.

Costco sometimes has a Eneloop kit you can buy with like 12AA and 4AAA with the wall charger and the little inserts to make the AA's into C and D batteries.

Your not going to get 20Ah in series.. Your going to need to add a few parallel stacks.

Boats, heavy duty car stereos, etc will use car batteries in parallel to get more Umph and more up time.

Getting into and using different stacks can be dangerous when charging. You should isolate a stack once it is fully charged so the stacks don't overcharge each other. Battery isolators can be cheap or expensive.

#12 ohata0

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Posted 25 August 2013 - 09:34 PM

i see. when connected in series, the voltage increases, but capacity stays the same. when connected in parallel, voltage stays the same, but the capacity increases.

so in order to get 8 ah using the eneloops, you'd need to connect 4 packs (8-10 in series) in parallel.

hmm...that's a lot of batteries.

#13 Jon Isaacs

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Posted 25 August 2013 - 10:42 PM

They are connected in series. Connected in series, you get 13.4 volts with 20 amps of capacity.



Eddgie:

That is not the way it works.

Ten 1.34 batteries 2 amp-hour batteries in series provides 13.4 volts at 2 amp-hours. The current is not multiplied as it passes through each battery, the current through the leg is constant.

Current is the rate of electron flow, it is measured in amps = coulombs/second, a coulomb is about 6.2×10^18 electrons. My father used the water flow analogy to teach us... amps is like gallons per minute.

Think of a battery as a water pump.. Pressure = voltage, current = water flow.. If you connect two pumps in series, you double the pressure but the flow capacity does not change. If you connect them in parallel, you can pump twice as much water but only at the pressure that a single pump provides.

To get a 13.4 battery with 20 amp-hour capacity, it would require 100 1.34 volt 2 amp hour batteries, 10 groups of 10 each wired in Parallel all wired in series.

8 Alkaline D cells can provide about 15-20 amp hours at 12 volts.

Jon Isaacs

#14 Eddgie

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Posted 26 August 2013 - 08:07 AM

First, I may have made a mistake about running dew strips. I do not use them and did not consider the added load.

The capacity is independent of anyting else. If you have 10 2 amp batteries, you have 20 amps of capacity. It does not matter if they are wired in series or parallel.

What determines how much current you can deliever to a load is how the batteries are wired.

But what detemines how much current you draw is the load.

If your load never draws more than 2 amps, then it does not matter how the batteries are wired because in both configurations you never get less than 2 amps.

I see what you are saying about runnig a dew strip though.

The amp hour capacity is the same regardless of how they are wired. What differs is the maximium current you can draw, but if your load never exceeds more than 2 amps, then the batteries in series will be fine.

The load determines how much current will be consumed and if you have a two amp load and 20 amp hours of capacity, that will run the load for 10 hours.

I was wrong though that you would be able to run a dew strip.

But my Go TO mounts all use 2 amp power supplies and the Eeneloops all measure out at 2 amp capacity.

These batteries run the mount with no problems.

Agian, I was wrong about the dew heater. I don't use them and should have thoght about it more. The title of my post was running the mount, and I oversteeped to include dew heaters. I should have thought about it more.

#15 Jon Isaacs

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Posted 26 August 2013 - 09:27 AM

The capacity is independent of anyting else. If you have 10 2 amp batteries, you have 20 amps of capacity. It does not matter if they are wired in series or parallel.



Eddgie:

Please listen. This is basic electricity, first year physics. It does matter if it is wired in series or parallel. Why would you bother to wire anything in parallel if wiring it in series provided the same current capacity? Parallel means the current adds, series means the voltage adds.

One can look at this from the standpoint of conservation of energy. Each AA battery has a certain amount of electrical energy stored, the amount of work each battery can do. 10 batteries has 10 times the energy of 1 battery.

The energy stored in a battery is:

E = Amp-hours x Volts

For convenience sake, assume that each AA battery has the capacity to provide 2 amp-hours at a constant 1.39 volts.

E = 1.39 x volt x 2 amp x hours x 3600 seconds/hour = 10,000 watt-seconds = 10,000 joules or 10 KiloJoules (kj)

Each battery stores 10 KJ worth of energy. 10 batteries = 100 KJ.

13.9 volts at 20 amp-hours, how much energy is that?

E = 13.9 volts x 20 x amp x hours x 3600 seconds/hour = 1,000,000 watt-seconds = 1,000,000 joules = 1000 kilojoules.

10 batteries of 10 kilojoules each provides 100 kilojoules, not 1000 kilojoules.

Jon

#16 Eddgie

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Posted 26 August 2013 - 11:50 AM

Explain this then.

Here is a 8 Vdc pack using 6 Enelope batteries.

The picture is showing a Multimeter set up to measure 10 Amps. Check the setting. It is easy to see in the picture.

Note that this 8 volt supply is pushing out 5.75 amps. When I first hooked it up before getting my camera and taking some pictures, initial current draw was over 6 amps.

Now this represents far more load than I normally put on a pack. My normal load is about .7 amps when tracking and about 1.8 amps when slewing.

The new Go-To dob runs about 2 amps when slewing, but I never draw more than about 2 amps from the pack at one time.

Attached Files



#17 Jon Isaacs

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Posted 26 August 2013 - 12:21 PM

Explain this then.

Here is a 8 Vdc pack using 6 Enelope batteries.

The picture is showing a Multimeter set up to measure 10 Amps.

Note that this 8 volt supply is pushing out 5.75 amps.

Now this is not mouch different than a short circuit, and this would run down the pack to zero in about 2 hours. As time goes on, the current will of cousre fall, but as you can see, the output of the pack is not limited at all by the capacity rating of an individual battery.


Eddgie:

First: I would not recommend shorting out your AA batteries as you have done in the photo, they will get very hot and even explode. I am not sure what type you are using but in general it is unsafe to short out any battery.

As far as you demonstration.

Consider the definition of amp-hours. It's a rating of the stored energy, not a rating of the maximum possible current. In the simplest form: a 2 amp-hour battery is capable of providing 2 amps for an hour. This is not really true due to efficiency issues.

So, if you draw 5.75 amps from a 2 amp-hour battery, it will last approximately:

2 amp-hours/5.75 amps = 0.35 hours or about 21 minutes.

But I would definitely not try to see how long the batteries last, it is dangerous.


Also note that your 8 volt supply appears to be nearly shorted out. If you had a second voltmeter, you could measure the actual voltage across the terminals and see that it is not 8 volts because of the internal resistance of the batteries.

Jon Isaacs

#18 Eddgie

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Posted 26 August 2013 - 12:39 PM

Well, the battery is not shorted really. It is just running though a low resistance load.

And remeber this is an 8 volt pack running into about a 2 ohm load and well that is not really what I use the pack for because none of my equipment draws amps of current.

Of course someone implied earlier that you could not get more than 2 amps out of the pack if the batteries were wired in series, so maybe my meter is incorrect or something.


Thank you for correcting my misunderstanding of how these things work and sorry for the mistake.

I apologize for wasting eveyones time.



#19 Jon Isaacs

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Posted 26 August 2013 - 12:49 PM

Well, the battery is not shorted really. It is just running though a low resistance load.

Knowing the voltage as being 8 volts and the current as being about 6 amps, we can calculate the load as being 1.33 ohms.

But the meter leads start to get very hot within about 30 seconds, so I am limited to short periods becuase I don't want to melt the meter leads.

Each battery is putting out .5 amps and they batteries don't heat up nearly as fast as the meter leads.


Eddgie:

Please draw a circuit diagram for 6 batteries wired in series. The most basic rule in circuit analysis is the current in a leg is constant. Currents in series elements are constant...

Each battery is putting out 5.75 amps if it wired in series. The circuit diagram is simple, all the current passes through each battery.

You do not know what the voltage across the batteries is because they have internal resistance. You need to measure the voltage at the terminals.

Take your first year physics book and study circuits, single loop.

Jon

#20 cn register 5

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Posted 26 August 2013 - 12:56 PM

Try doing the same thing bas well as the meter add a 6W car side light bulb in series. That means:
Battery + --- bulb --- meter set to 10A ---- Battery -

The meter should show about 0.5A current.
Note the time at which it starts and run it until the batteries are flat. How long did it take?

If your assertion is correct it will take 40 hours. If what Jon and I are saying is correct it will take 4 hours.

Chris

#21 jrcrilly

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Posted 26 August 2013 - 01:24 PM

Each battery is putting out 5.75 amps if it wired in series. The circuit diagram is simple, all the current passes through each battery.


Yes.

The root of this confusion is the inappropriate mixing of the terms "Amps" and "Amp-hours". If you want to compare energy density in differing voltage conditions it is necessary to use a measurement that includes voltage; in this case Watt-hours is appropriate. For round numbers, let's consider a stack of 2 Amp-hour, 1.5V cells. Each has a capacity of 3 Watt-hours. As Jon and others have explained, a series stack of ten 1.5V, 2 Amp-hour cells will yield 15 volts at 2 Amp-hours, or 30 Watt-hours. That's correct, and we could have gotten there by simply multiplying 3 Watt-hours X 10. 15 Volts at 10 Amp-hours would require 150 Watt-hours. You are only using 10 cells of 3 Watt-hours each so there's only enough energy there for 30.

#22 tecmage

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Posted 26 August 2013 - 01:36 PM

Agreed. By definition, elements in series have the same current flowing THROUGH them, and elements in parallel have the same voltage ACROSS them. If I put 10, 1.5V batteries in parallel, the voltage across them is 1.5V. If I put those same batteries in series, and measure voltage across them, I get 15V.

You have to be careful with multimeters. They have a little internal resistance to prevent the meter from changing the values you're trying to read. I usually get one student a semester that blows the fuse on a meter because they used it wrong.

#23 GeneT

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Posted 26 August 2013 - 10:14 PM

Great information Eddgie!
GeneT

#24 John Carruthers

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Posted 27 August 2013 - 02:17 AM

Best demo I've seen is the early electric submarines where batteries were switched between "Group up" and "Group down", short and fast vs long and slow.

#25 Midnight Dan

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Posted 27 August 2013 - 06:23 AM

Of course someone implied earlier that you could not get more than 2 amps out of the pack if the batteries were wired in series, so maybe my meter is incorrect or something.


No, you can easily get more than 2 amps out the batteries as your meter is correctly showing.

Amps is a measure of how much current is flowing, not the capacity of the batteries. The capacity is measured in amp-hours, at a particular voltage, and is found by measuring how long the batteries can continue to deliver a certain amount of current.

If you set up your batteries with a resistor so they are delivering say 5 amps, and they last for 1/2 hour, then the capacity is 5 times 1/2, or 2.5 amp hours.

And Jon is correct. If you put any number of 2 amp hour cells together in series, you still only have 2 amp hours, you just have it at a higher voltage.

-Dan






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