Re: Batteries in Parallel
 

Well if you're primarily trying to power laptops... why not just let the laptops run on their internal batteries for the 5 seconds it takes to change a battery?

Also, inverters don't much like computers, and vice-versa.

Inverters are a very dirty power source, and tend to make a square wave, as opposed to a the true sine wave coming from your local power utility. This wreaks havoc on the electronics of a computer's power supply.

Conversely, computers suck alot of power. I'd be surprised if that inverter didn't have trouble powering even 1 computer, including monitor... ESPECIALLY if you're using a CRT... those things are ridiculous amounts of power hungry. I've got a couple at home that cause the lighting in my house to surge when turned on.

Re: Batteries in Parallel
 

At full power and 90 % eff. that equates to almost 75 amps input. Remember that a computer produces a pretty steady load once it is on. If you choose the power saver options then hard drives will spin down and monitors will sleep when not in use. At 60 amps, our robot batteries will only stay above 10 volts for about 6-10 minutes.

V(f) is the forward voltage drop across the diode when it is conducting. The lower voltage drop is what you need and a forward drop of 0.3 volts is an indication that you are looking at a Schottky diode. Normal silicon diodes have a drop of 0.6 volts.

A switch is likely to give you enough interuption that a computer might get upset. You might be better off with a substantial UPS than an inverter.

Re: Batteries in Parallel
 

Just another $0.02... Last year on our way back from Atlanta, I brought 2 batteries on board the bus so I could connect my laptop to my (I think) 400W inverter. I only used one battery, and I used it for over an hour until I got tired and shut it down. I know someone else had their cell phone connected to it as well. Also, my laptop's power cord is rated at 70 watts, but I'm sure it pulls much less when the battery is not charging and I'm not running a graphic intensive game. I'd say a 600W inverter would be good for maybe 4 laptop for about 20 minutes, then the battery will go dead. This is just guesswork as I do not now the rating of your laptops. The video camera will last probably all day on one battery, and the inverter will probably pull more current to run itself than to run the camcorder. With 100% efficiency, you could probably run a camcorder for 2 days straight. I do agree with what someone said above... if you're going to be running laptops and a video camera, and all likely have a battery that can hold a charge for longer than a minute, why not just connect the inverter to a battery using alligator clips or make an adapter, and connect it to only one battery?

Re: Batteries in Parallel
 

The only laptops our school lets us borrow are the 7 year old ones with various broken parts. The ones we had for this year's regionals had zero battery life (really zero, not even 5 seconds).

The inverter is modified-sine-wave (square except for a zero period in between extrema), and the laptop power supplies are switching i believe. Not sure if switching power supplies handle the square waveform better or worse...


Thanks for the information- it didn't make sense that a diode could only handle .31v max! I am looking into getting that second diode mentioned (the one with the big terminals)

See above- and it's not just those electronics I want to run. I'm building this because I just got really tired of needing power where there were no outlets in sight. Anything's better than having to do all the data entry for scouting outside the arena.

Laptops and camera are just an example application- I can see this being used to run most anything-
- power drills if working outside
- printers on laptops
- a router (if theres no power at the location it needs to be to get signal everywhere)

I know it's not ideal for certain applications, but it's definitely universal.

Thank you for all your input, I think I have enough information now to continue work. If I remember, I'll post stuff when I'm done (pics, how long it lasts, ideal applications)

Re: Batteries in Parallel
 

In that case, you can't get much simpler than having one of the boat battery switches. I got one this summer for our t-shirt shooting robot for around $25... then I drilled some holes in it, put some JB Weld one it, and basically ruined its original purpose, then stuck it to our robot, attached a pneumatic piston to it, and have a very nice battery selector switch. If it can handle running 2 CIMs, 2 Compressors, a Van Door Motor, and 3 Neons, then I'm sure it can handle just 1 inverter. The one I bought was a Perko Dual Battery Switch (http://www.cabelas.com/prod-1/0001497012970a.shtml) that I bought from a local store. The one in the URL is exactly like it, but more expensive, so I'm sure you can find a cheaper one.

Re: Batteries in Parallel
 

Ladies and Gentlemen,
I know this thread has been idle for a while but I have received some guidance on parallel batteries from engineers at both MK and The Battery Council International. Both sources believe that batteries of the identical type with the same physical condition (age, identical charge/discharge cycles, identical charge condition, similar production runs and no physical damage) should be capable of being placed in parallel without protective diodes. However, both sources recommend diodes when any one or more of these conditions cannot be met. Further the Battery Council recommends using fuses (at the batteries) approriate to the wire size used to connect the batteries in parallel with or without diodes. Both sources also believe that as discussed in this and other threads, dissimilar batteries will cause current to flow from one battery to the other. Diodes protect against this flow. That is all for now. Have fun in Atlanta.