Power requirements?

[OK Apricot]

Good afternoon ladies and gents, 

In short, I'm trying to figure out what power supply I'm going to need to power my rig in the field. The equipment that needs power:

EQ6-R Pro, (will be) ASI533MC-Pro, ASI120MM-Mini, Lynx astro 2" & 4" dew straps, Lenovo Thinkpad laptop. 

I've found the power draw for the dew straps - 0.33A & 0.67A respectively. I'm not sure on the power draw of the other bits of equipment. Could anyone shed any light on the rest? 

The idea is that I run all this kit off an inverter from the van using a slave battery of sorts. I can plug an extension in and then get the appropriate 240V adaptors for the mount, dew straps etc. Could I plug say a Nevada PSU into the inverter and run everything from that? Am I making sense? 

[ONIKKINEN]

The easiest and most reliable kit for mobile astrophotography is one of these, or something equivalent from another brand: https://www.amazon.co.uk/Portable-Station-Generator-Adventure-Emergency/dp/B0B2DHTBPM/ref=sr_1_9?crid=1SUNU2DQLB5HC&keywords=jackery&qid=1659885029&sprefix=jackery%2Caps%2C108&sr=8-9&th=1

I have this one (doesnt seem to be sold in the UK): https://eu.ecoflow.com/products/river-portable-power-station?variant=37254607863972 . The 288wh model has so far never run out during a night, even down to -25 degrees. When i used my mini-pc off the AC inverter side it did almost drain out every night though, so i switched to just powering it with a USB-C cable. I would imagine your laptop is by far the weakest link in terms of power usage here, and one you might want to rethink if mobility and convenience is what you're after. If yours is a low power consumption model with power saving turned on, then maybe you can make do with just the battery it has for the night, but otherwise i could see that as an issue. Give the idea of using a mini-pc a thought?

Running 240V AC inverters from a 12V battery is very inefficient and you could run into issues with dropping voltage as the night goes on, so i wouldn't do this. Its far more convenient to have everything run off the same power station with 12V DC. Power draw will greatly depend on how much you cool the camera, but if you cool 15 degrees below ambient it will probably be around 1-2A of current drawn. The EQ6 will draw at least 3A when slewing at full power with a reasonably sized scope, and more than 4A if its cold outside (and if you are not balanced well). You should aim for a total of at least 7A of consecutive current being drawn, but to be safe maybe aim for up to 10A.

But if you really want to do the inverter off a battery and a second PSU to regulate, it would probably work just fine, but just unnecessarily complicated.

[OK Apricot]

Thanks for some thought. To be honest I just want to have enough juice to be able to get at least half a winter's night of imaging, somewhere around 5 hours. I just don't see my 7Ah skywatcher pack going that far with two dew straps, cameras and a large EQ mount running. The laptop battery will go for approx 2hrs on a full charge, it's only a refurbished jobby. If I could just keep that charged from an inverter that'd be great (I will need one on the van for work anyway). Budget may be a factor if I'm looking at £300+. 

[malc-c]

Your mount will typically draw around 2.5 to 3 amps when slewing, probably around an amp when tracking.  

I would agree with the above post, 7-10 amps total draw in total.  If your van is 12v system then just rig up a distribution box and connect it to the battery in the van.  Even if the van engine was running, most alternators put out 13 - 14v which is still fine for the mount.

[teoria_del_big_bang]

I too would not go for the inverter.
Think about it does it make sense to take nominal 12V (albeit more like 13.8 V DC fully charged) then boost it up to 240V AC only to reduce it back down through various power supplies to 12V nominal again.

It is not so easy to say exactly what amperage all your equipment will use, for instance the mount will depend on how often you are slewing to target as during a slew it may take 2 to 3  amps but when tracking will be more like 0.5 amps, so if you spend a long time slewing to different targets before you decide on an imaging run then your power source could last a little less than if you don't so all this messing about.
Also if you use a controller for your dew bands you may not have them at full power so could save some power there, also some nights you may not need them.
And then there's the imaging camera, the camera itself only takes about 0.5 A (spec says 0.65A)  but the cooler as rated at 12V 3A max, now I doubt it will ever take 3A but probably takes 2A when full on cooling, however, this will not be running at full whack all the time and also depends on how far you are cooling below ambient.
I am guessing your two CCD's are plugged directly into laptop and so take their USB power from the Laptop

Basically a 12V leisure battery would supply the 12V to nearly all your equipment for a cost of around £30 to £40 and then use one of THESE for the laptop. you would need to construct some sort of box with appropriate connectors for the battery there are a few threads on SGL where members have done this.

So taking averages that I have had an educated guess at I would say:
EQ6-R Pro 0.8A
ASI533MC-Pro 1A for cooling (0.5A from USB)
ASI120MM-Mini 0.1 A from USB
Lynx astro 2" & 4" dew straps  1A if not using controller so full on all night.
So 12V wise we are looking at around 3A so for 5 hours in theory a battery that is larger than 15 Ampere hours but as I say you do not want to run it fully down ever so probably looking at 25 to 30 A/Hr battery.
Something like THIS for £32

Lenovo Thinkpad laptop. I am not sure what current it would take , my thinkpad has a 20V  65W power supply so would take 3A at most I would think, but through the 12V adapter maybe more like 5A (all depends on what cooling it has to do, brightness of screen and processes running, USB connections etc) . so if using this you may need a bigger battery as this now takes the consumption to  more like the 7 to 8A suggested in above posts and then I think you are looking at a battery more like 40 A/Hrs to be on the safe side so might be more like £50.

Although the inverter is very inefficient if you are saying you will have the inverter anyway then try it but not sure what the efficiency would be and could waste 50% at least so again needs a bigger battery more like 100 A/Hrs or more so if the van battery is fully charged and a decent size then you might get away using that with the inverter but I would be careful there is enough charge left to start the thing after the session or get a 100 A/Hr battery (or more) and run the inverter from that and recharge at home (regularly even if not used it).

There are better types of batteries that do not need a much maintenance (leisure batteries or car batteries need to bee charged regularly even when not in use and must not be run down completely otherwise they can be damaged so that they are almost useless)  lithium ion are much more robust and do not need as much attention but the downside is they are expensive for the size of battery you are looking at.

Steve

 

Edited August 8, 2022 by teoria_del_big_bang

[OK Apricot]

Very good suggestions there Steve, exactly what I was looking for. Thank you! I like to think I'm handy enough with a soldering iron and some wood work so might be able to make myself a box of sorts. 

[malc-c]

Steve, have you measured the current drawn from an EQ6 or even your HEQ5 or was the 800mA a guess ?  I say that because when I tested the draw of an EQ5 with the 200P the smaller motors drew 1.96 Amps when slewing, but the initial torque to get moving was more at a round 2.45 Amp if I recall (was some time ago as I've had the HEQ5 for a decade now.  I would hesitate a guess that the larger steppers in the EQ6 is likely to draw more, especially when the extra torque to get the mount moving is needed. 

[teoria_del_big_bang]

7 hours ago, malc-c said:

Steve, have you measured the current drawn from an EQ6 or even your HEQ5 or was the 800mA a guess ?  I say that because when I tested the draw of an EQ5 with the 200P the smaller motors drew 1.96 Amps when slewing, but the initial torque to get moving was more at a round 2.45 Amp if I recall (was some time ago as I've had the HEQ5 for a decade now.  I would hesitate a guess that the larger steppers in the EQ6 is likely to draw more, especially when the extra torque to get the mount moving is needed. 

Malcolm, it was just a guess and I actually meant to change it to an average of 1 Amp, unless slewing around several times an hour or so I would think even for an EQ6 that would be a reasonable average current draw from a good 12V nominal supply (Which is probably more like 13V to 13.8V), but yes it's a guess so I could well be out - anyone with a EQ6 that has measured the currents could help with that one 🙂 .

I did actually check the power consumption on my HEQ5 sometime ago with the Esprit 100 and I seem to think that was around 0.5 A tracking and 2A slewing, yes you are correct there was an initial surge of current which with a meter set on capturing max current did get up towards 3A but was so transient I didn't really take much notice of, although if one of those nights when you are slewing a fair bit trying to decide on the target I guess could impact a little on my very approximate calculations.

I also did not factor in the fact it is a EQ6 not HEQ5 but assumed it would not be too much different - but again an assumption I admit 🙂 
But even then as I always then factor to buy a 50% or so extra capacity battery should not be too far out.

I think that without actually sitting down and measuring the currents it is difficult to guess to an amp or so and even measuring factoring in things like how much current over the night the cooling of the CCD will take as this is not constant also makes it difficult so always go well above the A/Hr capacity you actually need, maybe going 2X the calculations is even better.

Steve  

[Carbon Brush]

Do you own a multimeter? If not, why not?🤔
If you measure the current drain of various items in the daylight, you will have actual data, which is more reliable.👍

A caution on measuring dew straps. Measure current directly from the PSU without a controller.
Dew controllers turn the power on/off at intervals. You need to know you can provide the peak current.
The average current is useful for calculating battery capacity used.

Include a voltmeter in whatever power pack/battery/whatever you use.
It is much better to be aware of a battery approaching full discharge, rather than wat for strange effects on mount slew, etc.
Battery manufacturers publish voltage on discharge graphs. All 'fall off a cliff' at end of life.
The value depends mains on the battery chemistry.
If you watch for a few tenths of a volt above this point, you will know when to pack up or reduce load.

HTH, David.

[malc-c]

The problem is that three people could all measure the current draw, and get three different results unless they have the same weight of scope & kit hanging off it.  Often it's better to go by the manufactures technical specs listed on the retailers website.  The EQ6-R on FLO's site states 11-16v @ 4 Amps.   Now if in reality the actual current draw is less because the load is no where near the 20kg the mount can shift, and you have a supply rated at 4 amps or above then you should have no issues with the mount dropping out mid slew.

Another factor is most devices will list their power consumption / rating so you can always do a little maths to workout the current draw and take that as a ball park figure.

David's comments on battery chemistry is also important.  Some will hold charge almost right to the end and then drop off sharply, whilst others start to lose charge slowly from the start, so are un able to maintain the current draw even though the voltage is still showing 12v (Ni-Mh and Ni-Cad being tow examples).  Also temperature affects things too, with cold weather reducing battery performance dramatically compared to a warm summers night.

I have a 12v 60w (5A) mains power block in the observatory for the HEQ5, and have never had an issue with the mount. I also use the same power supply for powering the D400 via an 8.5v linear regulator stepping the 12v down.  

[teoria_del_big_bang]

14 minutes ago, malc-c said:

The problem is that three people could all measure the current draw, and get three different results unless they have the same weight of scope & kit hanging off it.  Often it's better to go by the manufactures technical specs listed on the retailers website.  The EQ6-R on FLO's site states 11-16v @ 4 Amps.   Now if in reality the actual current draw is less because the load is no where near the 20kg the mount can shift, and you have a supply rated at 4 amps or above then you should have no issues with the mount dropping out mid slew.

If we were talking about a mains power supply then yes I agree in an ideal world you should calculate the supply on all the maximum demands (like I say in an ideal world - in the real world very unlikely to get all devices demanding full draw at same time but if you do rate it like this then never should have a problem).
But pretty much all reasonable sized leisure batteries are capable of delivering pretty big currents that are well in excess of what an astro rig will demand so my reasoning for all the averaging of the demands is to get the capacity of the battery in A / hrs. When using a battery that is the important figure (I would think so anyway).

The one thing I did not mention is that if the OP does go with the inverter option (as that seemed an easy option for them) then yes we should consider maximum demand and not the average so a good point to note in this instance.
So taking maximum demands more like:
EQ6-R Pro 3A
ASI533MC-Pro 3A cooling (0.65A from USB)
ASI120MM-Mini 0.1 A from USB
Lynx astro 2" & 4" dew straps  1A if not using controller so full on all night..
So inverter needs to be capable of at lest 8A and better to go for at least 10A I would think.

Steve

Edited August 8, 2022 by teoria_del_big_bang

[OK Apricot]

Some good reading there, thank you. I would like some sort of mains power as well as I have an outlet outside in my garden. Just trying to brainstorm a solution to portability. I guess this would be a case of getting the Nevada PSW-30 👍. 

If I understand correctly, 8A @ 12V works out to be 960W. It wouldn't be anywhere near this in practice, but in theory say I got a 40Ah battery, using the numbers above should give 2-3hrs reliable power before voltage starts to drop for while I'm out in the field. 

[malc-c]

4 hours ago, OK Apricot said:

If I understand correctly, 8A @ 12V works out to be 960W. It wouldn't be anywhere near this in practice, but in theory say I got a 40Ah battery, using the numbers above should give 2-3hrs reliable power before voltage starts to drop for while I'm out in the field. 

You're a decimal place out - 96w.    (amps x volts - 8a x 12v = 96w)

Battery ratings such as 40A/h  means if you draw 1 amp it would (in theory) last 40 hours.  A 2 amp draw would run the battery down in 20 hours.... so an 8amp would drain the battery in 5 hours.  In reality it would be quicker as voltage also drops off and its very difficult to totally drain a battery to 0 amps and volts.  You're estimation of 2-3 hours is probably sound.

[Len1257]

When remote I use a 36Ah LiFePO4 battery. Powers a HEQ5 or GEM45 mount (with GT-81), two dew heaters, ASI2600MC, ASI EAF, Guide Cam and (via a convertor) a 19v Intel i5 NUC. Lasts a full night and judging from the output voltage probably would do 1/2 the next. Once the initial mount slews are done tracking doesn't take so much. The dew heaters and NUC are the more constant load. The battery management on a LiFePO4 battery prevents you running it down. 10V or so and it cuts off. Not a problem if it lasts all night anyway.

[Carbon Brush]

On battery capacity......

Lead acid are usually quoted at the 20 hour rate. So 40Ah gives 2A for 20h.
However, if you increase the current, the capacity is lower.
If you pull say 5A, don't expect 8h. It will be more like 5h, maybe 6h.
Lead acid starts out with the 'on the tin' capacity, but degrades every day from manufacture. Regardless of how nicely you treat it.
Always look for a manufacture date when buying a new battery.
The degradation is temperature related, so can be slowed by keeping the battery in your garage/shed. Today with 25C+ is an exception.
Do remember a lead acid battery performs poorly below 0C. In astro use, it is lower capacity.
There are aguments for the winter, keeping the battery outside until you plan a session, then bring it indoors for a few hours.
Don't forget to recharge or top up charge every month or less. You can easily wreck a battery by neglect.

Lithium provides the 'on the tin' capacity at a specific discharge current and a specific temperature.
If you deviate from these, capacity is a bit less.
They tend to degrade by the number charge/discharge cycles. Not the calendar. Good for intermittent astro use.
Life is often defined as them going to about 2/3 of initial capcity.
They perform well in the cold. They are 1/4 to 1/3 the size and weight of lead acid for the same power.
Self discharge is very low. If we have 6 months of cloud and you haven't checked the battery, no worries.

So for astro use and planning for long term use, it has to be lithium, if your wallet can take the hit.

HTH, David.

[ONIKKINEN]

The consecutive load of my AZEQ6 carrying an 8 inch newtonian, cooled astro camera, guide camera, mini-pc is somewhere around 25w when not slewing or the early parts of cooling the camera from my 13.6V power station. I dont have dew heaters so yours would be a bit higher, but the 40Ah battery would do the trick for you as long as its not very cold outside, or if you can keep the battery warm (like in the van). Disconnected "dumb" batteries lose voltage really fast under high load and you can expect the voltage to be no higher than 12v after some use. If temperatures drop below 0 it could get a bit more tricky. If temperatures drop below -10 i wouldn't bother at all with a disconnected battery.

When slewing the same setup can reach around 100w which would be more than 7 amps of current at 13.6V.

[OK Apricot]

Excellent, thanks guys. I will order a proper LIFEPO4 🙂👍

Edited August 9, 2022 by OK Apricot
Excellent, not "eventful"

[teoria_del_big_bang]

16 minutes ago, OK Apricot said:

Eventful, thanks guys. I will order a proper LIFEPO4 🙂👍

Really is best choice and in the end worth the extra cash I think.

Steve