Mach2 Slew Speed, Power, and Voltage Question #Mach2GTO


Greg McCall
 

Hi John,
That's excellent information and I much appreciate the detail. You have also raised something that I didn't consider yet with those popular power supply modules as I had not really seriously considered a 12v to 24v converter. You have also saved some effort in those current measurements so again, thanks for that detail.

(I wonder what the 12v current is just operating the Mach2 at 12v.  Something to watch next time. -- The AP spec of 5A minimum is not very helpful as you usually plan for a maximum both in power supply, cabling & fusing)

My LiFePO4 batteries use 14.6v but I know I can set the max on my chargers if needed and the float voltage is 13.8.

I also use a NUC with a 12v to 19v converter. It's designed to power a laptop in a car so I assumed it could handle at least the charge voltages of lead-acid. (just replaced the cigarette lighter plug with a powerpole connector)

cheers
Greg


Roland Christen
 

I have a trickle charger on mine and as long as the CP4 is drawing power, the voltage does not rise much above 24 volts. Perhaps a high current charger will produce a higher voltage because the mount is not using that much current. I also am monitoring the voltage and power with an in-line meter while the mount is running.

Rolando


-----Original Message-----
From: Greg McCall <emailgregnow@...>
To: main@ap-gto.groups.io
Sent: Wed, Apr 7, 2021 3:55 pm
Subject: Re: [ap-gto] Mach2 Slew Speed, Power, and Voltage Question #Mach2GTO

Rolando,
You don't charge a 24v battery at 24v.
Just checking one battery spec at https://enerdrive.com.au/product/epower-b-tec-24v-100ah-lithium-battery/
It can be 28.8v-29.2v for charging and 27-27.6v as a float voltage 
(that's for a lithium battery, specifically, LiFePO4 often used in astro setups, camping, RV industry)
24v is a nominal voltage with the operating range being 22v to 29v 
While I've not been given a specification for the allowed voltages, the discussion so far has indicated these voltages are not suitable for the Mach2

Contrary to what has been said in this message thread (and a similar thread), are saying I can use a 24v battery on the Mach2 while charging?
I just see no specification and now mixed messages.

--
Roland Christen
Astro-Physics


John Upton
 

Greg,

On Thu, Apr 8, 2021 at 04:40 PM, Greg McCall wrote:
While I've seen many discussions of the power bricks, I only do portable Astrophotography as I live in the centre of Sydney and must drive to a location. I currently use 12v (nominal) LiFePO4 batteries but was considering a 24v battery to power my Mach2. The alternative, a 12v to 24v booster (readily available from China) could be used, but I wonder about the quality of those available and the noise produced on the 24v output. This also seemed an obvious solution and wonder why AP has not suggested it leading me to think it may not be a good idea.
   One thing to keep in mind is that using a 12v to 24v DC-to-DC converter is that you might still have the same issue with running a charger during operation.

   My own LiFePO4 battery has a charge profile that requires up to 14.4 volts during the final absorption / equalization phase of the charge cycle. (The charger should then immediately switch to either float or monitoring mode.) The problem I would have is that the 12v to 24v power converter has a maximum input of voltage specified at 14.0v. Thus, charging the battery with the power converter attached could damage the converter unit.

   My own solution to this is to use my charger in "Supply Mode" where is becomes a fixed voltage float charger or "power supply" outputting a fixed regulated 13.6 volts. This allows some recharging of the battery while in operation without endangering either the battery or the voltage converter. Many of the high-end chargers have a "Supply Mode" setting -- both my CTEK and NOCO chargers support that manual form of operation.

   If you wish to use a normal Lithium charger on your battery during operation, you will need to carefully scan the specs for whichever voltage converter you use to ensure it remains in spec during a charge cycle of your particular charger.

   Regarding the output of the voltage converters, I found the one I use to be pretty good. (I am not taxing it at all. It is spec'ed for 24v @10A output and the highest consumption I have measured on the 12v side is about 6.5 to 8.5 Amps.) I did monitor the output both steady state and during a voltage transient on the input side. At steady state there is about 0.2v to 0.4v ripple on both input and output due to the five switching mode voltage converters (5v, 12.6v, 13.7v, 19v, 24v) contained in my field battery box. The voltage transient happens when I power up my NUC using another 12v to 19v converter as indicated in my second message in this thread. Due to the impedance of the wiring in my battery box wiring, I see a ~75 uSec drop to 10v on the 12v input side. (That is the cause of the motor stall issue I mentioned in my second post in this thread. This takes about 3 mSec to fully recover back to 13.3v. The output of the 24v lead to the Mach2 shows only a similarly short drop of about 1v and fully recovers within 150 uSec as seen on the scope trace below.



   In the trace above, the baseline 0v level is the bottom grid line. Each grid is 5v vertically and 100 uSec horizontally.

John


Greg McCall
 

Hi Mike,
The first two things are that I don't use a keypad and I don't use or need a 3 stage charger. But I was also not just trying to solve my particular issue but to provide info so anyone who needs it is armed with the information. So an answer specific to me while very helpful, would be better for all if I could get AP to document the area.

While I've seen many discussions of the power bricks, I only do portable Astrophotography as I live in the centre of Sydney and must drive to a location. I currently use 12v (nominal) LiFePO4 batteries but was considering a 24v battery to power my Mach2. The alternative, a 12v to 24v booster (readily available from China) could be used, but I wonder about the quality of those available and the noise produced on the 24v output. This also seemed an obvious solution and wonder why AP has not suggested it leading me to think it may not be a good idea.

Lead Acid batteries, typically AGM or Gel construction for astro stuff, need a 3 stage charger with the absorption voltage at about 80% charge level which is around 40% of the charging time.
I use Lithium Iron Phosphate batteries (LiFePO4) which are a type of lithium that are close to matching Lead Acid voltages. 
These are a safe type of Lithium battery (compared to Lithium Cobalt-based batteries is used in say a mobile phone) and also used in Recreation Vehicles, camping etc. They also charge at full charge current for 100% of the time, can be safely discharged to around 80% compared to 50% of lead-acid, are under 1/2 the weight and have way more charge-discharge cycles.
I particularly favour some locally made (in Australia) high-end batteries (read trusted brands) that have a built-in state of charge and current monitoring as part of the internal battery monitoring system, that I can BlueTooth too with an app if needed during the night.

LiFePO4 batteries have some slightly higher voltages compared to Lead Acid.

The reason I would have liked to see a definitive specification is that I know what gear I have and AP know what they have. I then can choose a solution that meets both specifications.
I didn't expect AP to test the variations (particularly on a world stage). Specs take the guesswork out of decisions and not rely on what the world seems to be moving to opinion-based decisions based on numbers of votes. Many opinions actually don't override facts and I would have liked to see the facts from AP in the form of a spec or definitive recommendation.

I also understand voltage drop and the need to err for thicker cable with shorter runs. I also have multimeters to confirm the various voltages. I typically use oversized cables, quality fuses and powerpole connectors to reduce the voltage drop.

I also only use quality chargers. In my case, I favour Victron smart chargers with the Bluetooth app.
The charger also has its own cabling and fuse to the battery.

regards
Greg


michaeljhanson@...
 

Hi Greg,

I hear two different questions.
1) What is the max permissible input voltage to the CP5?
2) Can I use a 24V battery charger.

For question 1, no one likes to hear, "it depends".  So, the keypad has a max input voltage of 28.0V.  This is where the 28V "specsmanship" number, mentioned in the other thread, comes from. 

This answer is unsatisfying, so we can be more pragmatic by entertaining question 2 instead of question 1.  I think this is really what you are wanting to understand.
A proper three-stage charger can provide up to 29.4V absorption voltage at the max absorption set point.  This exceeds the keypad rating.  Are you even using a keypad???
If not, the next "limit" is the transient suppression, which can begin conducting at 29.5V.  While the margin sounds low, the suppression voltage has a large positive temp coefficient when it begins to conduct, and, there will be losses in the power cable to the CP5 contributing to margin.  So, the margin is much higher than it seems.  So, if you do not have a keypad plugged in, I see no issue using a battery charger. 

Suppose you DO have a keypad.  Do you know the absorption set point of the charger?  Does the charger even have an absorption set point? If so, do you have control over it?  Does it transition from absorption to float properly (does it even have a float stage)?   Can you measure the highest charge voltage?  If the answers are "no", I would be reluctant to have a keypad plugged in while charging.  Reason is, there's just too many crappy chargers out there, with no possibility of us testing every one of them.  An absorption voltage set point can be as low as 28.2V.  We know that, even with the mount parked, there will be a couple tenths drop in the power to the keypad through two harnesses.  *IF* you know the absorption voltage to be at the low end of typical, I see no issue using a charger even with a keypad.

I hope this helps.

Regards,
Mike Hanson


Greg McCall
 

Rolando,
You don't charge a 24v battery at 24v.
Just checking one battery spec at https://enerdrive.com.au/product/epower-b-tec-24v-100ah-lithium-battery/
It can be 28.8v-29.2v for charging and 27-27.6v as a float voltage 
(that's for a lithium battery, specifically, LiFePO4 often used in astro setups, camping, RV industry)
24v is a nominal voltage with the operating range being 22v to 29v 
While I've not been given a specification for the allowed voltages, the discussion so far has indicated these voltages are not suitable for the Mach2

Contrary to what has been said in this message thread (and a similar thread), are saying I can use a 24v battery on the Mach2 while charging?
I just see no specification and now mixed messages.


Roland Christen
 


Having a 24v system and not allowing for use of a 24v off the shelf battery (with charging) seems to be a poor design.
Where did you get this idea? You certainly can use a 24 volt battery with charging to power the Mach2.

Rolando


-----Original Message-----
From: Greg McCall <emailgregnow@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 31, 2021 8:22 pm
Subject: Re: [ap-gto] Mach2 Slew Speed, Power, and Voltage Question #Mach2GTO

I was more hoping by now a more specific answer was available as I've never seen a manufacturer not have an actual specification for their equipment.
Having a 24v system and not allowing for use of a 24v off the shelf battery (with charging) seems to be a poor design.
12v or 24v are usually nominal voltage based historically on a car or truck battery systems. (with an appropriate voltage range for charging and discharging batteries)
Using a mixture of batteries to get close to the voltage is just not practical. 

--
Roland Christen
Astro-Physics


Greg McCall
 

I was more hoping by now a more specific answer was available as I've never seen a manufacturer not have an actual specification for their equipment.
Having a 24v system and not allowing for use of a 24v off the shelf battery (with charging) seems to be a poor design.
12v or 24v are usually nominal voltage based historically on a car or truck battery systems. (with an appropriate voltage range for charging and discharging batteries)
Using a mixture of batteries to get close to the voltage is just not practical. 


michaeljhanson@...
 

HI Greg,

The limiting factor the the upper end of the voltage range is the threshold at which the transient suppression begins to conduct, which will have a very wide tolerance.  This topic was discussed in the other forum a while back, here:
main@ap-ug.groups.io | Max Voltage Question got Mach2GTO/GTOCP5

The general consensus on that thread seemed to be that having a CP5 powered directly by a battery that is also being charged was discouraged. 

Cheers,
Mike Hanson


Greg McCall
 

Mike,
that’s very helpful. It sounds like 20v into GTOCP5 is the min for 1800x
If 24v is the nominal, what is the max voltage?

(context: max charging voltage for a 24v battery)

cheers
Greg


Seb@stro
 

Thank you Mike! Much appreciated!

Sébastien 


John Upton
 

Mike,

   Thank you so much! That seals it then; I will continue to use the 24 volt converter for a dedicated power connection to the Mach2. I can understand the need for the hysteresis although I had not considered that aspect before. Nice touch! Thanks again for the details.

John


michaeljhanson@...
 

Gents,

To answer the prior question, the input voltage threshold for limiting the max slew speed to 1200x is 19.0 volts on the way up, and 18.0 volts on the way down.  Meaning, you're limited to 1200x until the input voltage rises above 19.0,  Once it rises above 19.0, you'll retain 1800x unless the input voltage then drops below 18.0. The 1.0V hysteresis window is to avoid "flickering" back and forth between thresholds.  Realize there will be losses in the power cable, and a (Schottky) diode voltage drop in the unit as well.  So, the input voltage seen by the GTOCP5 will be lower than what is reported at a power supply.  This means a 19.0 volt power source will not quite allow you to get 1800x slew rate.

Regards,
Mike Hanson


Seb@stro
 

John,

I am where I want to be. I am using a NUC10 system with an i7 six core processor. I spec'ed it that way for several reasons.

Of course, only you know your requirements.  With such a beast, I suppose you can Live Stack, watch a 4K/60fps movie and play GTA-V while you do planetary imaging... (Does it make coffee ? kidding 😉). To me, apart from low power, size and weight were also a main consideration as it'll be piggybacked on an EdgeHD 8 + small refractor riding the Mach2.

FWIW, the NEO comes with 8GB DDR4 2400MHz (upgradable to 16) and a Quad-core CPU clocked at 1.5 GHz (turbo up to 2.8), 240GB SATA SSD and only cost around $300. But I haven't tried it in the field yet, so real world power consumption is TBD.

Nice battery box BTW.

I am a bit surprised no one from AP answered your original question yet (max slew speed vs input voltage threshold). That would interest me as well. For now anyway, I'll stick with 12V all around as I don't need the ultrafast slewing.

Sébastien

_._,_._,_


Kenneth Tan
 

Most NUCs will run on 12 v but if it drops below that it will Cut off. So better to be higher or if not to get a voltage stabiliser

On Tue, 30 Mar 2021 at 20:57, ap@... <ap@...> wrote:

That’s not necessarily true.  If you browse the specifications at the Intel site, it varies a lot.  Some generations are strictly 19v, some are a mixture of 12-24v, some 12-19v.   It varies by CPU (maybe and kit but it looked more like CPU).

 

The marketing literature is often vague, but Intel publishes the actual requirements.  Here’s an example side by side of two 11th gen models:

 

https://ark.intel.com/content/www/us/en/ark/compare.html?productIds=205038,212519

 

The first is 19 only, the second 12-24.

 

Buy carefully.

 

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Tom Blahovici via groups.io
Sent: Tuesday, March 30, 2021 12:18 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Mach2 Slew Speed, Power, and Voltage Question #Mach2GTO

 

Hi

BTW, if you are using an Intel NUC, 19V is not necessary. They work just fine at 12V as per specs.
My NUC is an i5 with SSD, and thurnderbird 3 to 10G Base T adapter. It works reliably with no issues.
Might save a little space and battery power.
Tom


John Upton
 

Seb@stro & Kenneth Tan.

   Regarding the suggestions that I need a lower power mount-side computer, I am where I want to be. I am using a NUC10 system with an i7 six core processor. I spec'ed it that way for several reasons. You are right that DSO imaging is not very taxing on a PC. However, there are other imaging methods than just long exposure DSO and some of them require more compute cycles from the CPU.

   I built my mount-side mini-PC to be power efficient in normal use. The NUC is running with 16 GB RAM and 500 GB fast NVMe storage. If I turn it loose, it draws as much as 90+ Watts. However, I use a custom configuration which allows it to run DSO imaging at an average of about 12 W with an average of 15% CPU utilization. I think that compares well to lower end Mini-PCs which run at similar power levels of 8 to 12 W at 50% or higher CPU utilization.

   I have plenty of battery power available to me. As of now with the Mach2, it is about the highest power consumption component of my imaging rig. My testing so far is showing a total power usage of about 35 Watts with the Mach2, cameras, and NUC (running Cartes du Ciel, PHD2, Sequence Generator Pro, APCC Pro, and PixInsight (also with a low power configuration)). Prior to the Mach2, this was running about 24 W with my SkyWatcher mounts so the Mach2 has increased the power draw substantially. (For the benefits, though, the Mach2 is worth that extra current it uses.)

   My last set of changes for my Mach2 addition is to rewire my DIY battery box for direct output to the Mach2 using only Anderson PowerPole connections. I currently use the standard astronomy / automotive 12 v cigarette sockets for all power plugs on the battery. (That was done because I once saw a person at a regional star party whose imaging was shut down due to a failure of a custom PowerPole power cable for his rig. No one else there had a spare PowerPole cable to loan him. Lots of folks had spare cigarette cables to offer. The lesson learned by me is to make up spares of any custom cables or else keep them all standard.)

   I knew that the cigarette plug was the weak link for higher currents. It has served me well but I had never had a need to draw up to 7+ Amps through one before. It was interesting to see the effects of significant overheating inside the plug from the Mach2 high speed slews.

John


John Upton
 

Tom Blahovici,

On Mon, Mar 29, 2021 at 11:18 PM, Tom Blahovici wrote:
BTW, if you are using an Intel NUC, 19V is not necessary. They work just fine at 12V as per specs.
   This is not true of all NUCs. The one I am using specifically specifies that 19 volts +/- 10% (or is it 5%) is required. My NUC came with a 120 Watt power brick and doesn't always boot at 13.3 volts from the battery. Many to most of the older i5 and lower NUCs will run fine from 12 - 19 volts and even state so in the specs. This one does not.

   The main thrust of this thread is about the Mach2 power requirements. Specifically, I was looking for information on how far below the 24 volt specifications you lose the ability to slew at full 1800X sidereal speed. In the end, I find I must use 24 v for other reasons and will continue on that path.

John


John Upton
 

Kenneth Tan,

On Mon, Mar 29, 2021 at 11:08 PM, Kenneth Tan wrote:
I used these and they work well for me. Comes under various brand names but all look exactly the same.
   I am already using two similar devices to those you linked. One is the 19v version for the mount-side NUC and the second is the 24 v Version I am using for the Mach2. They were both referred to in my very first post as "potted DC-DC Converters". Both function very well. I have used them before on other projects also which is why I had a few sitting around as spares.

John


ap@CaptivePhotons.com
 

That’s not necessarily true.  If you browse the specifications at the Intel site, it varies a lot.  Some generations are strictly 19v, some are a mixture of 12-24v, some 12-19v.   It varies by CPU (maybe and kit but it looked more like CPU).

 

The marketing literature is often vague, but Intel publishes the actual requirements.  Here’s an example side by side of two 11th gen models:

 

https://ark.intel.com/content/www/us/en/ark/compare.html?productIds=205038,212519

 

The first is 19 only, the second 12-24.

 

Buy carefully.

 

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Tom Blahovici via groups.io
Sent: Tuesday, March 30, 2021 12:18 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Mach2 Slew Speed, Power, and Voltage Question #Mach2GTO

 

Hi

BTW, if you are using an Intel NUC, 19V is not necessary. They work just fine at 12V as per specs.
My NUC is an i5 with SSD, and thurnderbird 3 to 10G Base T adapter. It works reliably with no issues.
Might save a little space and battery power.
Tom


Seb@stro
 

Just bought a Minix Neo J50C-4 Max with similar features and performance to the LattePanda Alpha but with Quad-core CPU instead of dual and comes in a case + VESA mount. DDR4 memory and M.2 SATA SSD upgradable. No arduino. 10Watts.