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Mounting an inverter


cjdawson

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Hi all.

My battery box project has been really successful.  However, as with everything, there's just one more thing that I want to add to the device.  This time it's a 300W inverter.  I have the inverter already, but it has no fixing holes.    I don't really like the idea of opening it up and modifying it. (something about 240 volts makes me not want to modify a metal box).

To mount the inverter, I would like to have it inside my big battery box. (there is plenty of room for it)  Been thinking about this and I'm settling on the idea of cradling the inverter with a plastic box, that I can cut up to allow better access to the switch and plug.  Also at the other end to allow good airflow for the cooling fan.

My question is, does anyone know of a good place that supplies boxes that would could be suitable for this?

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Before fitting the inverter, check whether the out put is 'clean', i.e. if it outputs something closer to square waves as opposed to sine waves, then some equipment may not function, and any induced signal, into the DC lines may also have unintended consequences... 

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Good advice by Julian, Not to say a cheaper standard inverter would not run

your equipment but you would probably be doing so with added risk

Ideally you want a pure sine wave inverter, its as close to the mains power

supply as you are going to get,

If you are going to stick it in a plastic box make sure the box is big enough

to incorporate a fan, as inverters do get warm, they get warm under load

but also they are not 100% efficient and that is turned into heat by the process

that makes the voltage go from 12 volt to 240 volt.

also as you will be dealing with 240 volt outside, it is also advisable to put a short circuit

mains protector in line if the invertor does not have one built in, so if something does go

wrong it should protect you from a mains shock.

Paul

 

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Maplins do a good range of plastic boxes for electronics.   

As well as Julian's advice re how clean the inverter is, have you checked the power and current implications for your batteries?    If you are going to be drawing anywhere near 300W then that is going to put a hell of strain on 12v batteries - even assuming 100% inverter efficiency, 300W would draw 25 amps from a 12v battery, and drain a 20Ah battery in under an hour.    If you are just powering a laptop then you may be OK though you should factor in a realistic power loss for the inverter, eg if you have a 40W laptop, and 85% inverter efficiency you will still be taking 4 amps from a 12v battery which is still quite a significant load.

 

 

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The overall box that the inverter is going in is one of these 

http://www.diy.com/departments/jcb-deep-tool-cart-w465mm-d480mm/1000636_BQ.prd?gclid=Cj0KEQjwwry8BRDjsbjMpPSDvagBEiQA5oW0nO9aRY_-qKniOjjsam4jsxUAh4IvJY766Wih7wdmecMaAr-U8P8HAQ&ppc_type=shopping&ecamp=SEAPLA1000636_BQ&ss_kwcid=AL!3454!3!{creative}!{matchtype}!{placement}!{network}!{product_partition_id}!{keyword}&CAWELAID=120147360000498329&CAGPSPN={ifpla:pla}{ifdyn:dyn}&CAAGID={adgroupid}&CATCI={targetid}&ef_id=VrnjpAAABJ48P02I:20160720120328:s

 

Thought I'd posted up pictures of my power box sometime in the past.   I'll get some snaps tonight and post them up.

The inverter will be powering my Apple MacBook Pro 15" (retina) only.  All the other equipment on my scope is run from 12v.

I've already tested that the inverter will happily run my laptop, so that's all good.

 

The intention here is that I'm going to have the inverter cradled in a box that's mounted to the inside of the jcb box.   The power supply for the laptop will be plugged directly into the inverter.  And there will be a small slot cut into the lip of the box to allow the low voltage part of the power cable out of the box.  That way, all of the 240v stuff is locked away inside the box.

 

The inverter that I have is one of these

http://www.outdoorgear.co.uk/Ring-PowerSource-Inverter-300W-sku53162101.asp?gclid=Cj0KEQjwwry8BRDjsbjMpPSDvagBEiQA5oW0nDGxpKlS6ON4JiwPQYY0o4hvpJRGoXqgAK3H7bU5pIAaAnN48P8HAQ

 

I tried it last night using a battery to power the inverter.  The laptop worked fine, and so I don't think I need to worry about whether it's a pure sine wave or modified sine at this point.

 

The question about noise on the DC side is something that I had not considered.  I think some further investigation there would be prudent.

I have access to basic electronic tools, and an ossiloscope as well.  So it should be possible to test out if there's any noise.  Just need to know what I'm looking for, and how to setup a reliable test rig.

 

 

For those interested.  I'm thinking about adding a second battery box soon.  the plan there is to use XTC-60 type connectors to allow the two batteries to be connected in parrellel.  this way, I have my current box with a 70Ah Leisure battery, this one makes a great camping box, with lots of plugs for powering different devices - including now a 240V socket.  Then I'll be able to link in another battery which I already have (another 70Ah Leisure) which will give me a total of 140Ah of usage!

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3 hours ago, cjdawson said:

 Then I'll be able to link in another battery which I already have (another 70Ah Leisure) which will give me a total of 140Ah of usage!

That should keep things going nicely :)

 

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Now that's an idea.  I could get a piece of aluminium bar, bend it to shape and drill holes for nuts and bolts to hold it in.  That would then hold it to the side of the box so that it doesn't move.  I love it.  might even have a piece of alumium 3mm thick bar that I can use!  it would be perfect if it's long enough.

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I've just installed the inverted (It's not mounted yet) and have done a basic test to see what happens when it's all plugged in.

Basically the battery DC voltage remains stable, so I'm not worried about back feed messing up the other kit running from the battery.

Also, when I'm running the laptop with Nebulosity powering my Meade DSI, the inverter is pulling about less than 2 amps of 12v.    when I start up VM Ware fusion and boot into windows (so that I can access my Tucam) the inverter pulls just under 6Amps. Again the 12V DC line remains stable, so I'm happy that there's no back feed.

Tomorrow, I'm headed out to pickup a piece of aluminum, that I'm going to bend and cut to form a bracket to hold the inverter to the side of my power bank, so that part of the project will be working just fine.

 

 

however, I've had a setback.  I'm glad this happened now rather than after I build the next part of the project.

 

I mentioned that I was going to have a second battery connected in Parrellel, to give my a possible 140Ah of runtime if I thought I needed it.  With my 70Ah battery, it would run my setup for probably about 10 hours at full power, which should be plenty for a full nights observing.  Having the 20Ah run time would be much more desireable though, so I'm looking to get the parrellel connection up and running.  So what's the setback.

 

I built into my powerbox, an XT connecter using these.

 

http://www.ebay.co.uk/itm/5-Pairs-XT60-Male-Female-Bullet-Connectors-Plugs-for-RC-Lipo-Battery-Useful-Best/111850436197?_trksid=p2045573.c100506.m3226&_trkparms=aid%3D555014%26algo%3DPL.DEFAULT%26ao%3D1%26asc%3D20151005190705%26meid%3D8b3134c9eabc419e8a0194a7c186434f%26pid%3D100506%26rk%3D1%26rkt%3D1%26

 

mounted using this.

http://www.ebay.co.uk/itm/New-XT60-Panel-Mounting-Kit-US-End-/151553631904?hash=item23494ce6a0:g:CbUAAOSwmrlUt-fl

 

 

The problem is that one of the cables has just come loose.  Looks like the solder has failed to hold the joint securely.    Now at this point, I can tell you that it's never been powered up, so it can only be a mechanical failure from when I was moving the battery around.    I'm going to have a look at repairing the joint tomorrow, but I've just lost confidence in the idea of using the XT60 connectors.

So I'm now wondering about alternate methods.  Ideally I want to rate this part of my system at 30 amps, it should be complete overkill.  The idea here is to be safe rather than sorry.

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Nothing at all wrong with XT connectors.  Another good connector are the EC5's.  EC5's you solder out of the case and then push the bullet into the plastic whilst warm to secure it

https://www.electricwingman.com/ec5-connector

Anderson Power Poles are also a good product but as with all these a good connection depends on your soldering skills and equipment

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Any I'm done.  Inverter is wired in and mounted inside my power box.

Photo 23-07-2016, 16 20 31.jpg

The mount is made from a piece of 1.5mm aluminium which I've bent to shape around the inverter. It's holding it tightly to the side of the box, as well as being a tight fit on the inverter itself.  No danger of that thing moving.

I'm planning on drilling a hole somewhere above the inverter to allow a cable out of the box.  This is a job for another day once I have the right part to fill the hole.  I want some sort of cap that will either flip up and allow the cable through, or something made from rubber that will let the cable pass and seal up around it.   I'm liking the idea of the slip up thing better but need to find something suitable.

There's enough room to keep a 12v hair dryer in the box as well (not that I'll use it often, it pulls about 16 amps!)

 

For those that haven't seen the rest of the box here's some piccies to show you how it's put together.

Photo 23-07-2016, 17 14 11.jpg

This is the complete box, The inverter is inside on the right hand wall.   The small panel on the front shows the charge left in the battery, it's not wired in properly yet. Will be connected to the switch for the built in volt and ammeter.

Photo 23-07-2016, 16 20 44.jpg

Here's a close up showing the Volt and ammeter.  The Ammeter uses a shunt (basically the meter only measures a portion of the total current and works out what the full current is) and will measure up to 50 amps. 

The XLR socket is a 12v supply that I use for my telescope.  This is a locking connector, so I don't have to worry about cables falling out.

 

Photo 23-07-2016, 16 20 47 (1).jpg

At the bottom of the side panel, I've added 2 points for clamping jump cables.  The cabling behind this part is rated for about 500 amps, not that the battery can deliver that much power.   The smaller black plug above is an XT60 connector,  this will be for connecting external battery packs so that they work in parrellel to the one inside the box.  This lets me upgrade the overall deliverable amp hours.

 

Photo 23-07-2016, 16 20 38.jpg
Back to the front panel, and I've put in 4 usb sockets and 4 marine 12v sockets.   I decided to use marine parts here so that they can have covers to keep dust out.  In addition the 12v sockets can accept the marine 12v plugs, these have bits that stick out and lock into place unlike the car version.  Much more secure if I were to use them.

 

Photo 23-07-2016, 16 21 13.jpg

And of course, the whole lot is wired in properly.   Everything is fused, so there is not concerns about safety.  The cabling itself is rated for about 500 amps for the jump start points to the battery.  30 amp cabling is used throughout the rest of the wiring apart from the new inverter install which uses cable capable of 50 amp.

 

In astronomy use, the most that I'm likely to pull will be about 7amps.  So from the internal battery, that's about 10 hours use from a full charge.  

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Your battery will last longer the less you pull out of it (even assuming it's a leisure/deep discharge type), and I wouldn't expect a full 70Ah at 7 amps. You should be OK with a 7-hour session though if you aren't at full discharge all the time.

Yuasa suggest that if you discharge a leisure battery to 50% you will get ~70-350 discharge cycles depending on quality.

http://www.yuasa.co.uk/info/technical/understanding-leisure-batteries/

There's some useful formulas here:

http://www.streetmusician.co.uk/batterycalculation/

A street gig is probably not far from an observing session!

 

I have to confess I recently swapped in a new deep-discharge 'golf cart or stairlift' lead acid battery for a 'burglar alarm' in a high current application and the difference in performance and actual capacity was stunning.

Sorry if that seems like party pooping, but if helps you avoid killing your battery in a few deep discharge cycles...

 

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I don't expect the full amount from a battery ever.  Actually, the way that I work it out, is that I simply take the rating of the battery, then 1/2 it.   So my 70Ah I treat as if it's a 35Ah battery.  This is why I'm looking at getting my external battery part of the project up and running.  That way, I can have to 70Ah batteries, each I treat as 35Ah, so that means I'd expect to be able to get 70Ah of real world usage out of them.   Then looking at the other side of the equation. The 7A that I quoted earlier is also me over egging the cake a bit.  That's the figure for having everything running at full power.   Let's disect what I'm actually powering and you'll see the difference between my 7A and what I expect to be a more typical value.

 

1. Laptop,  This is only really needed when I want to power my DSI or my Tucam.  i.e. when I want to do imaging with a CCD camera.   I've mostly been using a DSLR, so don't need the laptop turned on at all.   (0A solution)

My Laptop is actually a MacBook Pro.   One of the selling points of these machines is that they are battery efficient. Apple has done lots of work on OSX to reduce the overall power consumption of the machines.  They've added features that sync up internal timer events, so that rather than having them going off all the time, they all happen at the same time, meaning that the processor runs in short sprints rather than processing all the time.  That's just one feature that I know of, and it's not something that you would even notice or spend time thinking about.    The end result, is that my 2015 MacBook pro running through the inverter uses between 1.2 and 1.6 amp of 12V.  (Lets over egg that a big and call it 2A just to give a bit of overhead)

My Toucam Pro II doesn't work with Nebulosity on OSX, so in order to get that working, I've had to come up with another solution.  For this I need to fire up an instance of windows running though VMWare Fusion.  This is much more power hungry and it pushes the amps up to something between 4 and 5 amp. I'm not sure if there are any tricks that I can do with VMWare (that I've not already done) to lower the power consumption. It's on my todo list to figure that out.  Anyway, running the Tucam pro II via windows software works great, and it doesn't add any more power consumption over what's already being used by the laptop. So, that's 5Amp.

 

2. Telescope (Meade LX-90)

Normally, for most of a session the scope spends its time tracking rather than slewing.  When it's tracking I've measure that the scope is using something around 200mA.

When slewing in both axis at full speed, it can use 2A.  However be aware that it's not going to be doing this all night, so it's more logical to guess at maybe 300mA average use over a full battery charge.

 

3. Dew heaters.  (I have 2 of them)

On some nights I don't need these (0A)

Normally, I'll run these at something like 25% of their maximum.   This works out that between them, they are using about 200mA of current.

At full power, they are using about 1A in total, which is more than enough to keep my scope clear on the worse of nights.

 

4. Auto Guider

I use a SkyWatcher synguider as an auto guider, this is why I don't need the laptop all the time.   obviously, if I'm doing visual oberving, it's turned off.

Normally, I'll use it for DSLR photos.  The synguider pulls less than 100mA when it's running.

 

5. SkyFi

This is a nice to have, I don't need it if I'm looking at easy to find targets. (0A)

Normally I do turn it on and use it from my iPad to control the scope.  It's great to use SkySafari visually see where the scope if pointing.  It's also useful when trying to find objects to help me star hop into place when the scope doesn't point directly at the object. (100mA)

 

6. Light panel

I have an EL Panel that I use for taking flat frames.  I like that I don't have to wait for morning.  This is only used for short bursts, so I'm not going to count it in the figures.  Just pointing it out for completeness.

 

7. Hair dryer

This is for that rare occasion when my scope dews up.  It uses 1A when blowing only, and a whopping 16A when heating!   Again I'm going to exclude this from the figures as it's not something that I want to use, it's a just in case to save a session that would have had to end.  Besides, there's always the option of powering it from my car rather than the telescopes power supply.

 

So here's me totals.

 

Lowest power mode.

Laptop 0A

Lx-90 200mA

Dew heaters 0A

AutoGuider 0A

SynGuider  0A

SkyFi 0A

 

Total 200mA

 

Medium power mode

Laptop 2A

Lx-90 200mA

Dew Heaters 200mA

AutoGuider 100mA

SynGuider  100mA

SkyFi 100mA

 

Total 2.7A

 

High power mode

Laptop 5A

Lx-90 300mA

Dew Heaters 1A

AutoGuider 100mA

SynGuider  100mA

SkyFi 100mA

 

Total 6.5A

 

So rounding things up, it's 1A for minimum, 3A normal and 7A maximum.

 

Frankly, I think things will be just fine ;-)

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The next part of my plan to get mains power for my lappy, means cutting a hole to let the power lead out.   My initial thought was to cut a slot that would fit the low voltage part of the power brick out.   As I was installing the inverter today, I got to thinking about it's secondary use as a camping box.  With that in mind, I've changed my mind on the original plan.

 

My new plan is to cut a hole in the side of the box big enough to pass a uk mains plug though.  I'd like the hole to have a flap that I can lift to let the power cable out.  At this point, I'm stuck again as I have no idea whether such a device exists, or where to get one.  So it's hunting time.

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1 hour ago, Stub Mandrel said:

Sorry, I was worried you might have been planning to run the lappie all night!

You clearly have it sussed but these postings might help the less experienced.

I figured you knew the deal, the breakdown is for less experience people.  The number of people that I see who are thinking about running everything for the whole night off a smaller battery makes me laugh.  Especially when they find out that their session is cut short by running out of power - just as that really cold crisp clear night settles down.  So there they up under a perfect sky, with not power. :)

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Only issue with inverters are some laptops don't like the cheaper modified sine waves versions. Apple's laptop power brick makes some nasty noises and the final word on that was to use the pure sine wave output inverters.

 

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@NickK I get that there might be problems with some power bricks.  I can only go by what I've been able to test.  On that score the 85W power supply with a MagSafe2 connector seems to behave properly on my modified sine wave inverter from Ring.

I'm not saying anything other that it works with my one power brick.  It might be that I'm lucky with mine.  It might also be that my inverter is a better quality one.  I dunno.   It works so I'm happy.

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In theory most SMPSUs ('power bricks' without transformers) should work find even with a DC supply as they filter then rectify the AC input before doing anything with it. It seems that some have power factor correction circuitry and it may be this that causes issues with the Apple ones.

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