sizing an inverter

[troypiggo]

I'm looking at inverters for when I only have 12V supply, but am a little bit electrically-challenged (or is it electronically-challenged?) and need some help. There are a few questions sprinkled through this post in italics that I need help with.

I already have a little Belkin 140W (300W peak) inverter and have been using that to date, but suspect I'm pushing its limits. Think it was designed for just notebooks mainly.

I'll be getting one from Jaycar. Notice there are 2 pages of them. Some are "pure sine wave" and some aren't. Important for the usage mentioned below? Massive price difference.

So what am I running through this inverter? This is a list of the things that I will probably run off it. Everything else I have already runs off 12V supply.

* Netbook - adapter says 240V 1.2A in, 19V 1.58A out. Which do you use for calculating the watts required? I assume it's the input, but that's 240x1.2=288W isn't it? Way more than the Belkin can take, but it does work fine. 19x1.58=30W may be closer to making sense? I know you can get DC/DC adapters, but I've looked in the past and the plug for this Aspire One doesn't appear to be one of the standard ones.

* MacBook Pro - may start using this more and the netbook less, so probably instead of the netbook. Adapter says 100-240V 1.5A in, 16.5-18.5V 4.6A out. I've had a bit of a look for 12V supplies for these, figuring they'd be readily available, but can't seem to find one. Similar question to above, what are the right watts?

* 2 powered USB hubs. No idea about their requirements, but figure pretty nominal?

* 40D with AC adapter - says 240V 45VA in, 7.8V 2A out. Isn't a VA the same as a W? Does that mean it uses 45W?

Should all of the above be used for the "normal" rating of the inverter as opposed to the surge/peak? How do you know what surge/peak power capability is required?

[DavidTrap]

Couple of things,

For Macs - there are no Apple 12V adaptors. There is a company in the US who will cut your power supply cable and put a plug in so you can swap between the AC adaptor and a DC-DC adaptor. Google is your friend.

The Mac adaptors are about 85W - if you do some image processing you may go close to drawing this current (do the fans on the Mac start running, if so you are working the processor hard and drawing lots of current)

Your netbook is putting out 38W, but the input is 240x1.2 = almost 300W. This would make it extremely inefficient. I would guess the netbook adaptor would consume 50-60W, allowing for 20% inefficiency of the adaptor.

My USB hub would consume ~20W max. You are right about the camera adaptor 45VA is the new terminology for 45W.

I would guess that a 300W Inverter would do the job for you (assuming you may want to run both laptops), but maybe 500W would be safer & allow for expansion.

Personally, I use a modified sine wave inverter without difficulty. Many will argue that computers need a Pure Sine Wave inverter - my sparkie mate told me that the power adaptors cope quite well with a modified sine wave inverter supplying their 240VAC.

Just my 2 cents worth,

David T

[beefking]

the output on the power pack for the netbook would be the power it requires - a 12Vdc/19Vdc conversion would result in a fewer losses than converting dc-ac-dc. If you intend to use the AC-DC converter you have, then you need to allow for the input power.

well, sort of and, no. The most watts it can draw will be 45W, but if you were to measure it, it may be less. It means that the current required is the same as a 45W load, even if the measured load in W is less.

yes, all the above ratings should be used to size the normal rating. Surge rating lets the user know how long the inverter can overload for before being damaged e.g. a 300W inverter might be rated at 350W for half an hour or 400W for 15 minutes. I think it's to do with the heat dissipation from the electronics.

Surge ratings may be important for a varying load, one with motor inrush or something that exceeds the normal rating. It would be safe to assume that the loads listed above would be pretty constant. Any inverter sized to cope with the constant load should be able to supply startup currents to your equipment for the short time they'd be present.


It might be worth tracking down a portable power meter (I think there are one's around called "kill-a-watt"s) and just checking how much your setup actually draws - the rated values may be quite conservative.

[troypiggo]

Thanks guys. Been thinking about this overnight some more. Wondering if those fairly high ratings on the notebook adapters are allowing for the case where it's charging the notebook battery as well as running the thing. So if the notebook is already fully charged, it will draw much less?

Still, sounds like I've been pushing the capability of the Belkin and risk it overheating or something. It has a fuse on the back of it, so hopefully that would protect equipment from damage, but still...

Looking at Jaycar inverters rated for 300W, there's one for $85 (http://jaycar.com.au/productView.asp?ID=MI5104&CATID=8&form=CAT&SUBCATID=680) and the closest one with pure sine wave is 380W and it's $270 (http://jaycar.com.au/productView.asp?ID=MI5162&CATID=8&form=CAT&SUBCATID=680)! Worth that much more, considering that DSLR AC adapter and the notebook adapters both may handle non-pure sine wave type input a little better from what I've read? (The USB hubs don't, though)

[Barrykgerdes]

Watts =Volts times Amps. This is the pure DC power
VA = Volts times Amps. An AC term meaning roughly the same. The Voltage is the RMS Volts times Amps but if the current and voltage are not in phase (power factor) the actual power will be less

I think this is right

Barry

[troypiggo]

Thanks for the clarification, Barry.

[mswhin63]

I would run laptop directly on batteries instead of an inverter, try:

http://jaycar.com.au/productView.asp?ID=MP3463

I use this a lot for more than just laptops.

[troypiggo]

Thanks Malcom. Couple of questions if you don't mind.

* It mentions 7 attachments incl Apple. Do you know if that would include my MacBook Pro? I'm new to all things Apple and not sure if their connectors are standard or different for each model.

* I see it has adjustable output voltages, but only mentions 3.5A out. As per my OP above, the MBPro adapter has "16.5-18.5V 4.6A out". I guess I could use 17V or 18V setting, but what about the 4.6A?

* How would you run several items off it at the same time? eg my powered USB hub etc. With the inverters I was linking above, I'd just use a power board type thing.

* When you say you run other things of it, not just notebook, what type of things do you run off it? How do you connect them if it's intended for laptops?

[mswhin63]

Blimey, your laptop draws lot of current so I suppose it is not going to work well, to higher risk of overheating. My and my wifes laptop only draw 3.3A.

The PSU(Power Supply Unit) primary design suggests a laptop but like any PSU it will work on anything else. I sell these as I have a whoesale account with Jaycars supplier for a number of Grey Nomad that need assistance with listening system while travelling.

It can be used for anything that has a DC power input as long as it can handle the current.

I think your only alternative is a DC-DC inverter. I am preparing my car with 80AH sealed LA batteries with a 750W inverter to supply other item. I would still use the laptop PSU to supply the laptop as the efficiency will be better.

[rally]

A DC to DC converter working at its normal ratings is usually about 85% efficient, I am guessing that a 240v Inverter is possibly similar or less and a 240v power supply unit is similar or maybe even worse.

That means you could potentially be wasting 15-25% of your batteries energy in all of these conversions - I dont know what their idel current draws are, but they could be a hidden killer !

If you are going out in the field there may be some benefit to having 240v for other devices, on the other hand there might be a benefit of not having 240v lying around on the wet ground ?
Only you know that.

I chose the DC/DC converter route and made up different leads with pkugs an sockets to suit so they couldnt get mixed up.

Check the voltage requirements of your USB hubs they are more usually 5v DC not 12v DC. (but 12v models do exist - just harder to find).
USB 2.0 Type A sockets are in theory rated to supply up to a maximum of 500mA (1/2 amp- 2.5watts) per socket, but a device has to announce itself as a high current device in order to be able to draw more than 100mA. So the required power for a USB 2.0 hub with say 7 ports can actually be quite high !
Of course if you know for sure that none of your devices draw this much power then you can cut down ?
If its a separately powered device then you are probably quite safe, but if the nly cord is the USB cord then it is also supplying power.

Assuming the Apple power jack is readily available and is just a simple 2 wire, it should be relatively easy to make up your own cable.

If you are removing the PSU's then I recommend that you fuse all lines appropriately for their purpose, otherwise you are bypassing an important safety mechanism.
I recommend that you fuse all 12v lines anwyay inless they are already fused

Hope that helps

[blueskies123_89]

Hi, sorry to bump into the thread from the middle of no where, but I'm looking for an answer to the same problem. I'm thinking inverters from car batteries are the way to go, heres one for sale on ebay for $31...

http://cgi.ebay.com.au/Car-DC-12V-to-AC-220V-Inverter-Adapter-100W-w-USB-Port_W0QQitemZ150369830401QQcmdZVie wItemQQptZAU_Car_Parts_Accessories? hash=item2302bd8601&_trksid=p3286.c0.m14

It seems so much cheaper than than the Jaycar unit linked previously, has anyone had a go with one of these?

[mswhin63]

A 300W inverter is a little more than double the price plus 220V not Australian 240V. It will most likely work better designed for people that are world travellers.

I personally wouldn't trust this unit but it quite possible to work. I am almost reluctant to purchace stuff from EBay anyway.

[Barrykgerdes]

Something that appears to have not been mentioned. What sort of load at 240 volts do you have. A 12 volt battery (car type or in a car) will quickly become discharged with any serious type of load. Don't get caught with a flat car battery at a remote viewing site.

I looked at this sort of problem and bought a "quiet" 2 KVA generator $600. It operates at the end of a 50 metre cable with a cover over it and won't be heard past 30 metres. It runs everything all night on about 5 litres of petrol.

Barry

[cfranks]

I have a couple of '12v to multiple voltage' inverters from Jacar and drive all of my equipment from a 12v battery, 75AH just increased to 150AH. They provide 19V for my Aspire One and 16V for my Gemini. Straight 12V for most of the rest.
Since I have them available for my Radio Control hobby, I use a 2 cell LiPo battery (7.4v) for portable power to my 40D. Excellent batteries but you need a special charger otherwise they explode:eyepop:. Finally a 12V to 5V regulator for the USB and Serial Port Hubs. Big tangle of cables when connecting and disconnecting in the dark!!
Charles

[blueskies123_89]

Well, a laptop (specifically my laptop) needs 19V at 4.74A, equating to about 90W. Plus a few accessories I don't think it will ever get near 150W... So an inverter around that range should do it. Does anyone know how many Joules a car battery can hold? That should give a good indication of the expected hrs theses things can power...

[beefking]

car batteries are designed for multiple small discharges of short duration i.e. lots of discharging to 95% of capacity then recharging. They do not cope well with being regularly discharged to deep levels - that's why you usually need a new car battery after you've flattened it a few times by leaving the lights on.

if you get a battery closely sized to your load, make sure it's a deep cycle one, or the life time will be... lacking.

[Barrykgerdes]

If a car battery had any decent "jewels" they would not be a problem to discard!

Baz;);):thumbsup::rofl::rolleyes::s crewy:

[mswhin63]

I would suggest not to use the car batteries unless you have a dual system and they are Deep Discharge.

Yu wouldn't want to go to a dark sky only not be able to restart the car. Serious Grey Nomads have dual batteries for just the purpose.

I will configure my sealed lead acid in the back of the car so I can get access to them along with unloading. I also have a small solar panel that I will use for recharging possibly while I am driving to dark sites.

[troypiggo]

I have a 75Ah deep cycle marine battery. Wouldn't use my car battery. I'd rather get another. Or a gen has been suggested by others also. No idea how to size one of those to meet my requirements. Yet.

[mswhin63]

The best way to size is work out the current draw for the equipment then the time expected to use it for. eg: 5A over 10 hours = 50AH I would the select the 80AH battery or higher. Solar charging is good to top up the batteries if you stay over a couple of days.

Generaly lighting now-a-days can be so easily done with high intensity LED's which draw the same current as low power LED's but generally double the power due to higher forward voltages to give almost 10 times the brightness.

For others munts and other equipment need to be taken into consieration to find the right AH.

As far as the inverter add the max power consumption to give the minimum power inverter maybe add 100W or more.

As I am typing this message outside in the freezing lovely night sky I am using a 20AH battery with a 750W inverter. Works well.

Be careful though if your inverter is too high for the power used it may not switch on. Some inverters require power draw to get them operating.

[mswhin63]

That is 5A at whatever battery voltage not mains (240V).

[Spanrz]

I just went through an experiment at Bathurst (Mt.Panorama) circuit this past week. I know this is a little off topic, but gives you an insight to what the result can be.

The Mrs and I went camping and I wanted to go all solar and battery powered. She was very dubious about it all, and I said "Don't worry about it".:screwy:
We had a Waeco 60lt fridge, a large HID-LED light (used in the mining industry for a headlight), a 300w inverter (12V) and a laptop.
I had 2 solar panels, both of the "Jackeroo" brand. One was just the panel and one was a panel with a battery pack (7ah).

Each panel gave me 13w at 0.75amp. The panel with the battery pack (i'll call this one a later model or 2 ver) had a switch that you could switch between 12v and 24v.
The older one went for $119 and is now sold out. The later one went for $140, but 1 week later, when I bought it went up to $199, I was &%%&^%.

Every thing I chose was 24v as much as possible, due to the fact that it draws roughly 1/2 the amps of 12v.
For 8 days of camping (in cool weather) I never ran out of battery power.
These solar panels did exactly what I wanted to do and more.
The fridge was set to -7c, and the laptop (using the 12v-240v inverter), the light and all the other stuff was sporadic use.

It is now my intention to run these panels, whilst using the scope.
It will be on 2 x 12v batteries (unsure of series or parallel yet). I do have a 240v power plug for the microstepping motor setup, but unsure how much power that will draw. I haven't done the sums yet. But the concept is to power the scope off 2 x 12v batteries. However the down side is carrying these 2 batteries in the car. For me it's no issue as I am used to moving large batteries around all day. The car handled 4 largish batteries (tractor) and all the camp gear, so it's all good.
The batteries I used were of a standard tractor/car battery design (not deep cycle), they were rated to about 100ah each.

As Malcom says, all lights should be of HID LED. The light I used draws 3 amps to get started and gets down to about 1 amp just to keep going.
It ran on 24v (2 x 100ah 12v batteries) for 4 days about 4-6 hours each day. Without a recharge, but I know it was getting low, might of got 1-2 extra nights of power but that would be it.

Even though I bought the panels for camping, I just solved how I will get power for the scope out in the bush. This is just magic. :)

Do your sums first, as power requirements judge what panels you use.

[MrB]

Nice one Brett.
I have a 65W solar panel to use when camping or when I eventually get back out to a deep sky site.

Please don't confuse HID and LED.
HIDs are Gas-discharge lamps, the most common consumer type used in car headlamps and torches etc is the Metal halide and Xenon short-arc lamp, basically a very small version of a camera flash tube that runs continuously.
Street lights (Mercury vapour, Sodium vapour and Metal halide) are also HID lamps.

[Spanrz]

Sorry Simon, I did get confused. I use HID's and LED's at work, should have put a "/" there.
The light I use, is an HID (gas arc) 24v 35W Nordic style light. Man that's got some power, but I might have to put a red film over for Scope stuff....Hehe.

I was going to opt for a solar system (not the planets one ;) ) around the 80w, but time and money got away from me, so 2 x 13w had to do.
I reckon that the solar with batteries is the way to go, for power supply in the bush :)

I just had a look at the power supply for my stepper motors, supplys 280w, and my inverter is 300w, I should just make it in suppling the scope with power (hopes).
I haven't done any conversions for power consumption just yet, but I might just run it for a bit to see if it works and how long it lasts on 2 batteries.
When I get the gearing system, in the next few weeks, it will come alive :D
Hoping by Christmas, I can have it going but the gears don't arrive till mid Nov.

[mswhin63]

The power supply would have a rating of 280W but the components would only use a portion of it. Depending on design it may only power 1/4 to 1/2 of the power supply rating.

Generally low cost devices use power supplies that run very close to their power rating whereas higher quality item run much less than there rated power. This is to conserve power supply heat.

The inverter should handle this quite well, I'd say.