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Powering the Paramount MX in the field

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#1 frolinmod

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Posted 05 September 2011 - 07:11 PM

If you have recently received a Paramount MX and are wondering how you're going to power it in the field, here are a few options:

1. The Software Bisque 48V LiFePO4 battery pack.

2. 12V battery + AC inverter + the included AC power brick (HUP80-18).

3. 12V battery + 12V to 48V DC-DC converter.

4. Four 12V batteries connected in series.

My Paramount ME uses very little power at 48V. It uses about 200ma while tracking, about 600ma while slewing at the default rate and about 900ma maximum while slewing at the maximum rate. The Paramount MX should be similar.

If you don't mind the up-front expense, option #1 is cost effective in the LONG run. LiFePO4 batteries are light, will sustain many charge/discharge cycles and have a long lifetime. It may seem like 5AH or 10AH isn't much capacity, but this is at 48V and thus equivalent to four times as much running time as at 12V. This is also just for the mount, not for all your other equipment. Therefore that 10AH battery may last three nights or more. This is a 48V battery pack, so it's only going to power your mount. You'll need another battery to power all your other equipment unless you can power it all off the 12V and 5V power output sockets on the MX control panel.

I think most people would find option #2 to be the easiest and most convenient while involving the least cash outlay in the short run. Note that AC inverters are isolated, which is good.

Option #3 requires some technical skill. It also requires that you fully understand that the DC-DC converter mentioned here is NOT isolated, so you may be subject to ground loops if you power more than just the converter with your battery. The easiest way to ensure that you will not have ground loops is to use a separate battery to power the converter than you use to power all your other 12V equipment (such as dew heaters, cameras, focusers, rotators, etc).

I recently did an analysis of option #3, using a 12V to 48V DC-DC converter. I found that option #3 was 40% more efficient than option #2 while tracking and 30% more efficient than option #2 while slewing at the maximum slew rate (100) and maximum acceleration (800) settings. Option #3 gets very close to the efficiency of option #1 or #4. Less than 10% difference. I measured this with my Paramount ME. The Paramount MX should be similar.

Option #4 is the most efficient option. I don't see too many people lugging around four heavy 12V batteries (or eight even heavier 6V golf cart batteries or whatever). But if you leave your batteries in your vehicle and run a long thick battery cable to the mount, it's certainly an option. 48V golf cart battery chargers are also readily available so that you don't even have to charge the batteries separately. You could run for literally weeks between charges this way.

#2 frolinmod

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Posted 06 September 2011 - 10:40 AM

I didn't make it very clear, but the main point of my post was to point out that using the 12V to 48V DC-DC converter is less than 10% worse than using an actual 48V battery pack and it beats the pants off using an inverter with the power brick.

I also forgot to mention the option of running off a nice quiet little Honda or Yamaha inverter generator. You might want to buy one of these awesome little gas sippers -- if you haven't already busted your budget buying the mount that is. They aren't cheap.



#3 jmiele

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Posted 06 September 2011 - 10:59 AM

Indeed. It's also WAY more cost effective than the SB 48v B-Pack. There again it's about 10% of the cost. :)

Thanks for the info. BTW, have you been motoring the power output? is it very stable? Does that unit "step up" generate much heat?

Joe

#4 vorkus

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Posted 06 September 2011 - 11:36 AM

Using 48V is very inconsiderate of the manufacturer. You can start a car on 12 volts why not run a telescope.

Voltage and current are inversely proportional. That means 4x the voltage means 1/4 the current. So if you convert your running current draws to 12v you get: .8 amps tracking, 2.4 amps slewing and 3.6 amps max slew. A large marine battery stepped up to 48V should still do the job for a night of viewing or AP.

#5 frolinmod

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Posted 06 September 2011 - 11:57 AM

BTW, have you been motoring the power output? is it very stable?

Joe, do you mean monitoring?

Yes, I have monitored the 48V (output) side of the converter as well as the 12V (input) side. The regulated output voltage does fluctuate a little bit as the load varies, but that fluctuation is well within specifications of both the converter and the power brick, so it doesn't worry me in the slightest. The 12V side also dips, both when using the converter and when using the inverter with the power brick, so I have to consider the voltage regulation of my 25A @ 13.85VDC power supply as a possible contributor here as well. I used a power supply for this test rather than a battery because I just didn't want to lug my extremely heavy deep cycle golf cart batteries from my garage around to my back yard. Those are what I normally use in the field. I'll reluctantly consider lugging the batteries around to the back yard and re-doing the test.

Does that unit "step up" generate much heat?

I didn't put a thermometer to the case, but it does remain cool to the touch. I don't think I can increase the slewing duty cycle to such an extent as to tax the converter much. It's a tiny little thing, but it's potted, sealed and most of the case is metal that dissipates heat well. It's probably not even breaking a sweat.

#6 frolinmod

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Posted 06 September 2011 - 12:28 PM

Using 48V is very inconsiderate of the manufacturer.

Well, not really. It's trivial for the user to just plug the power brick into an inverter instead of directly into a battery. No big deal. Being a software engineer rather than an electrical engineer, I don't pretend to have in depth knowledge of the reasons behind hardware design decisions and I don't feel qualified to criticize them.

Voltage and current are inversely proportional. That means 4x the voltage means 1/4 the current. So if you convert your running current draws to 12v you get: .8 amps tracking, 2.4 amps slewing and 3.6 amps max slew. A large marine battery stepped up to 48V should still do the job for a night of viewing or AP.

Yes indeed. It'll just run longer on the DC-DC converter than it will on the inverter and power brick combo, that's all.

#7 Kolenka

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Posted 06 September 2011 - 03:50 PM

Voltage and current are inversely proportional. That means 4x the voltage means 1/4 the current. So if you convert your running current draws to 12v you get: .8 amps tracking, 2.4 amps slewing and 3.6 amps max slew. A large marine battery stepped up to 48V should still do the job for a night of viewing or AP.


Just a minor nit. This rule of thumb really only applies to a system being passed through a transformer (stepping voltage up or down), since the wattage (power) is the same on both sides of the transformer. It's fine in this case, but it's not something I'd assume would apply to other situations haphazardly.

#8 frolinmod

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Posted 06 September 2011 - 05:04 PM

Just a minor nit. This rule of thumb really only applies to a system being passed through a transformer (stepping voltage up or down), since the wattage (power) is the same on both sides of the transformer. It's fine in this case, but it's not something I'd assume would apply to other situations haphazardly.

Thanks for the clarification. But the poster you quoted didn't write anything about power, only about current. What he wrote about current appears to be valid. What you wrote about power also appears to be valid. Hey, you're both right. The power is the same on both sides despite the current being different. However, if a transformation or conversion occurs from the 12V side to the 48V side, then there are real world inefficiencies and so the power on each side will not be the same. When a certain amount of power is consumed on the 48V side, even more power will be consumed on the 12V side. How much more power depends on the conversion efficiency. The DC-DC converter is over 90% efficient. Pretty darn good. The inverter and power brick are each about 84% efficient. 84% times 84% = ouch pretty low efficiency. But I only took two years of analog and digital electronics courses in college some 30 years ago, so I'm not an expert by any means. In fact, I think Ohms law is about my limit these days. Your clarification is very much welcome.

#9 Kolenka

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Posted 06 September 2011 - 06:44 PM

All three of us are right here. The rule of thumb usually assumes a perfect transformer with no losses to keep the math easy enough to do in your head.

Voltage, current and power are all related, since power is voltage * current. On both sides of a perfect transformer, power is the same. So voltage1 * current1 = voltage2 * current2. With that it's easy to see vorkus' point emerge. I just wanted to be clear that this is specifically a transformer phenomenon is all, for the sake of future readers. This phenomenon also makes it fairly easy to see the real loss in the transformer by comparing the actual power draw on both sides. :)

#10 vorkus

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Posted 06 September 2011 - 09:52 PM

My point is simply that we wouldn't be having this conversation if they had just found a couple of 12v motors. I know, 48v provides more torque at low speed, but still there are other ways around that. I think I'd look for four motorcycle/tractor sized batteries I could build a box around.

Btw, frolinmod you must have quite a beastly setup. How do you drag it into the field? Trailer? Dolley? Both?

#11 cbwerner

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Posted 06 September 2011 - 09:58 PM

I'm not knowledgeable enough to contribute much to this discussion, but I do think that in this case using the core technical terms would help alleviate some potential confusion by making clear how this discussion relates to the info people see on their equipment. So to that end . . .

Watts = Volts x Amps

To equate to the terms used in the discussion
- Watts = Power
- Volts = Voltage (akin to pressure)
- Amps = Current

So, to illustrate, in the discussion of 48v vs 12v, per the formula, a 12v setup must pull 4x the amperage to produce the same wattage as a 48v setup.

Hope that's helpful to someone. And carry on! I'm always eager to understand this stuff better. :)

#12 jmiele

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Posted 06 September 2011 - 10:23 PM

The Paramount MX and ME's are doing much more than just running a couple of DC servos. There is an entire PC inside. Several hubs (MX even has a USB hub now) as well as 12 VDC and 5VDC service lines. Additionally, a 12VDC high current power supply is now provided. This can be configured to run just about ANY high current camera/filter/AO config out there, Also, built in USB to serial converter.

This is accomplished via a higher voltage (48 not 12) yet standard sized power brick. I'll admit all 12VDC would be a tad easier, but I don't find the current config that inconvenient.

Joe

#13 urbanMark

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Posted 06 September 2011 - 10:43 PM

There is nothing on a modern PC board that requires over 5V. Most modern digital devices have no more than 3.3V IO with much lower core voltages. Even 3.3V is considered high for digital electronics these days.

Our mounts require 12V or higher simply for motor control. The 12V on a PC power supply is also used for motor control (disk and optical drives).

I suspect the ME and MX use 48V for powering the servo motors. Higher voltage motors generally have more torque. My CNC mill uses 48V for its motors - much easier to find high torque 48V steppers and servos than 12V. Of course they could have used an internal step up (boost) converter, but then the supply current to the mount would have been much higher (4x for the motors - IF you had a 100% efficient boost converter, which does not exist).

#14 jmiele

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Posted 07 September 2011 - 12:15 AM

The point was to identify that much is going on with this complex system. Someone stated it was inconsiderate to use 48v. I was attempting to point out that everything about these fine products is there for a reason. It's 48V because it should be. As these are the finest mounts available today..the better question is: why are all the rest doing it wrong. :)

Joe

#15 frolinmod

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Posted 07 September 2011 - 12:43 AM

Please note the big friendly smile on Joe's post. My intention was not to start a mount war, so let's please not have one. Thanks.

#16 jmiele

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Posted 07 September 2011 - 08:37 AM

Good point sir! It was said in jest. :) There are many fine mounts out there and 12VDC is working great for them.. The AP's would be one example, there are others. I can't speak to Steve's use of higher voltage motors i the Paramounts, however everything in these mounts is well considered.

The good news, for us Paramounters :) is Frolinmod has found that 48VDC is only going to cost us about 10% additional power running on battery.

Joe






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