I have been thinking about a project for a while now

[G+_Jason Perry]

I have been thinking about a project for a while now. Problem is today I think I blew the complexity out of the water.

 

I want to make a DIY version of a workstation on weels. My plan was to build a 2x2x3 box put it on wheels, put a post on the back of it to attach my monitor to and put my (or a) computer and UPS in the box. There is of course some additional addons for a keyboard and mouse.

 

Today I started thinking this wont really work the way I want it to. It will probably have to live tethered to a plug for power because of the inefficiencies of power supplies. If I really want this to work I am going to have to build an energy efficient PC, buy a crap ton of 18650s, and build a power circuit. Any thoughts on the feasibility of this project and if I should just stick to my previous plan?

[G+_Robert Short]

May want to research the portable workstations that they use at hospitals those are used with batteries primarily with everything you're talking about and then they just have to plug it in for power to recharge I check with my coworker later that works on site at a hospital to see if he can get the model or any information off of one of them next time he's over in the ER area

[G+_Matt Koglin]

Instead of a UPS, which are really intended for short-term power in situations where the electricity goes down, you might consider using a 12V deep cycle marine battery and inverter. Since you're running delicate equipment on it, spend the extra money for a "pure sine wave" inverter which outputs a much cleaner signal.

 

In my case, I have a photo booth that I wanted to be able to run off the grid. Loads include a small computer, photo printer, a couple of flashes, LED lighting and a T-Mobile Hot Spot. Let's assume that with everything running the average draw is about 250 watts.

 

At 120V (the output of the inverter), that's 2.08 amps (250W/120V). My deep cycle battery is rated at 85 amp hours, so I could theoretically run the photo booth for 40.8 hours on the battery. In practicality, there's overhead in the inverter and the actual battery capacity is lower than advertised. Plus, completely depleting a lead acid battery is not healthy for it. I'd count on a solid 20 hours of power from this setup if I needed to.

 

Downsides are the size and weight of the setup, but it sounds like you'd have plenty of room in your project box. Weight would be my biggest concern.

[G+_Jason Perry]

Hahaha, thanks Robert Short?, that's where I came up with the idea ours are Ergotron's. Maybe Ergotron's website will have more info. If your Co worker has any info on the inner workings I am interested.

 

I think if I go with my initial idea I am going to realize the steep limitations of a UPS, and if I go with my second, the circuit for the power supply will be a headache to build.

 

For the people out there who are going to say just get a laptop I am looking for a more robust solution.

[G+_Robert Short]

That's funny.

[G+_Jason Perry]

Matt Koglin?, you make a good point.

 

Does the booth have to go offline when you charge?

[G+_Matt Koglin]

Not necessarily. You can just attach a 12V battery charger to the rig. I recommend a slower charger, as it's better for the battery from my understanding, but it would depend on your needs. Keep us all updated on the status of your project!

[G+_Robert Short]

May want to check on the charging and power inverter design used for solar as the battery's would end up getting charged while still allowing power to the home/equipment like what the highway departments use. harbor freight has some cheaper models for prof of concepts I have used there parts to make sure thing work like i thought before buying quality part for a finished design or even improving their equipment to last.

[G+_Mark Quinn]

If you are going to use 18650 I would switch that to 26650 batteries due to the higher capacity and drain rate.

If looking at medical equipment power equipment I would look in the batteries they use to power portable xray machines. These batteries seem to last forever and and take a pounding.

[G+_Jason Perry]

Richard Craver?, that is exactly what I want to use. I seen a pfSense that uses either that or something like it.

[G+_Jason Perry]

Mark Quinn?, very good point. I was focused on the WoW, but there are all kinds of other pieces of equipment that are harder on batteries than computers.

 

Don't think too highly of the equipment though, the biotechnology department at any hospital has a big job to play with the endurance of equipment.

 

There is a possible KH episode I would like to see.

[G+_Jason Perry]

I did some research. The carts that gave me this idea have 2 33Ah 12V sealed lead acid batteries in them

[G+_Jason Marsh]

Matt Koglin Check your math. Drawing 2A at 120V from the inverter means the inverter will be drawing 20A from the battery. Inverters are a little lossy, so you'd be drawing more power (watts) from the battery than what the inverter is supplying to the loads. Not that you can't find videos on youtube of supposed self-running generator...

 

With a pair of 12V, 110AH deep-cycle marine batteries, you've got roughly 2.4KWh of power on tap, but only if you want to ruin them by deep discharging them. Pulling them down to no further than 50% State of Charge means you'll get about 1.2KWh, which theoretically would run a 250W load for about 4 hours. However, the faster you discharge a battery, the less net power you'll get out of it, and the worse you'll wreak havoc on the battery. Fast and deep discharges are bad for storage batteries, and you'll be looking to replace them far sooner than you might expect. Only drawing the battery to 75% SoC will yield improved battery life in both run time AND wear rate.

 

My own setup was with a pair of the 12V 110AH deep-cycle batteries, and ran a 30W load (modem, router, small NAS) for about a day before reaching about 75% SoC.

 

Other battery types, such as Lithium, while more costly per watt and more demanding in terms of battery care and feeding, will tolerate discharge and charge cycles better than lead-acid (automotive/deep cycle).

[G+_Robert Short]

just thinking, (dangerous for me) about the power loss of a battery charger and inverter circuit and then the PC power supply, and all your trying to do.

 

What about creating a regulated power supply that converts 2 12volt batteries to the different lower voltages for the PC +12, -12, +5, -5, +3.3. doing something like that may reduce the power loss and heat and only require 1 24v battery charger.

 

this would allow higher 12v amp draw if needed for drives and accessories. Not sure the best circuit but thats what this group is great for . I do know the 5 and 3.3 volts would need to be clean and stable as they are logic voltages but the 12v while need to be clean it's the power for motors and higher current needs. I think the most noise will be while charging. but also can come from external accessories while in use.

 

just a brain storm thought haven't heard of this exept the older suitcase PC from the 90's .

 

[G+_Jason Perry]

Thanks Robert Short?, my current plan is to use a DC to DC supply. I seen one in a pfSense video and someone hear sent me a link. The only thing I haven't decided is what to do for a charge controller. Then again I haven't looked into it yet.

[G+_Jason Perry]

I am starting to think it s going to be easier to go from 120VAC to a DC voltage a solar charge controller can take in. Unless I am searching for the wrong thing, all the reasonable options are for solar charging.

[G+_Jason Marsh]

If sticking with SLA batteries, you can find a charger for mobility scooters in the voltage you need. I have one for 24V sets, and another for 48V sets. If you need faster charging a big, honkin' golf car charger can be had in 24, 36, or 48 volts.

 

I think the PicoPSU (or similar) is the most efficient way to power a PC from batteries. I've seen them set up for 12V and 24V, and I imagine you can get them in others.

 

As for how to set up your battery bank, go with a series circuit. By increasing voltage you will draw lower amps to gain the same watts, and you won't bump against a low-voltage shutdown as early. If allows smaller primary wiring, as well, due to the decreased current.

[G+_Jason Perry]

Jason Marsh?, if I use a charger can I run the computer at the same time, or is it an either or setup? The solar charge controllers I was looking at will charge your battery and run the computer. I would just need a AC to DC converter in front of it.

[G+_Robert Short]

just found this site for battery power power supplies. (http://www.powerstream.com/DC-PC-12V.htm) might save extra steps

powerstream.com - High reliability 12V Input PC ATX computer DC-DC Power Supplies, 12VDC Input, car computer power supply, 12 volt, 320W, 450W, 500W, 650W, 1000W, ATX DC-DC

[G+_Jason Marsh]

I haven't seen those before, but I have no reason to think they wouldn't work fine. Probably about the same as the Pico PSU or similar. If they have one with a range of input Voltage, say 10V to 50V, you could test different battery configurations to determine which works best for you. I still think you'd be served best by higher voltage//lower amperage, as you'd have lower resistance loss from primary (supply)wiring.

[G+_Matt Koglin]

Jason Marsh Thanks for the clarification, and you're correct. I was off by a factor of 10. I've only tested my setup and never relied on it - which is probably a good thing. Whoops! In any case, don't drain a lead acid battery!

 

I like Robert Short's idea of DC-DC if your setup allows.

[G+_Jason Marsh]

I used AnyVolt (micro???) converters to supply 5V, 9V, and 12V rails from my 24V storage setup, a pair of 50W PV panels, and a scooter battery charger for midnight top-ups if necessary, to keep my internet and NAS running (mostly) grid-independent.

 

As for PV, it would take a long time for the panels I got for my setup to pay for themselves in, but it wasn't a project to save anything. It was just a project for the sake of tinkering. It served it's purpose and I still have it all, but the batteries died after about three years and I've since moved everything back to AC wall warts.