# Electrical engineers/electronics experts, I need assistance
**URL:** https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896
**Category:** Factual Questions
**Created:** [January 11, 2013, 8:13pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896 "2013-01-11T20:13:04Z")
**Posts on this page:** 10
**Page:** 2
### Author:  [@dexter](https://boards.straightdope.com/u/dexter)
#### Post date: [January 11, 2013, 11:00pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/21 "2013-01-11T23:00:48Z")
> [@beowulff](#):
>
> Not Sealed Lead-Acid batteries..
> That’s what the “sealed” means.
> Unless they are seriously overcharged, they won’t vent.
Quite true, but a lot of deep cycle batteries aren’t sealed. If the OP uses a marine battery from wal-mart, it might be “old school”. 🙂
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [January 11, 2013, 11:10pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/22 "2013-01-11T23:10:05Z")
> [@dexter](#):
>
> Quite true, but a lot of deep cycle batteries aren’t sealed. If the OP uses a marine battery from wal-mart, it might be “old school”. 🙂
Well, there is **NO WAY** I’d use a non-sealed battery in this application!
This means: **NO CAR BATTERIES**.
It’s way too easy to splash Sulphuric acid out of a non-sealed battery, and the fumes from a charging battery are going to ruin any electronics in an enclosed box.
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### Author:  [@PatriotGrrrl](https://boards.straightdope.com/u/PatriotGrrrl)
#### Post date: [January 11, 2013, 11:19pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/23 "2013-01-11T23:19:46Z")
> [@Michael63129](#):
>
> I can easily make an efficient DC/DC converter to replace the AC/DC power supply (yeah, the warranty will be void, but so what?), removing the original power supply to make room for the new one (if not on a separate PCB, remove the parts and stick the new board on top of it). This would save a watt or two for the monitor power supply and considerably more for the DC/AC inverter otherwise needed (another solution would be to make a high voltage DC/DC converter to supply around 150 volts to the monitor, which don’t care if the input is AC or DC since they use what are basically DC/DC converters, plus a rectifier, which would be a bit less efficient but still more efficient than a 50/60 Hz inverter). I’m assuming that for the enclosure, you can just use a readily available electronics enclosure (I’d use a case from some other electronics myself, the only thing I’d have to buy is the battery).
>
> ETA: Just adding in a DC jack to bypass the AC/DC power supply wouldn’t work in most cases since monitors often have two or more power rails, such as 3.3/5 volts for logic (an amp or two, so a linear regulator to 12 volts would be inefficient) and 12-24 volts for the backlight.
That’s old school thinking. Many monitors nowadays use a laptop-like power supply brick and thus have a standard DC input. The one I’m using now is 12V 3A.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [January 11, 2013, 11:31pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/24 "2013-01-11T23:31:59Z")
> [@PatriotGrrrl](#):
>
> That’s old school thinking. Many monitors nowadays use a laptop-like power supply brick and thus have a standard DC input. The one I’m using now is 12V 3A.
Yes, I agree. He should get a 12V monitor, which is the same as a 120VDC monitor, except the AC converter is external and can be removed.
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### Author:  [@dexter](https://boards.straightdope.com/u/dexter)
#### Post date: [January 11, 2013, 11:36pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/25 "2013-01-11T23:36:37Z")
Dang. Beowulff, I know you are going to think I’m trying start something, but I’m not. I consider you a knowledgeable and very helpful poster. But I happened to have a used sealed lead acid battery sitting behind my computer desk, and we are supposed to fight ignorance, right?
I don’t know if it is AGM or not, but it does say it is sealed lead acid, and nonspillable. Along with warnings not to incinerate or short the leads, it warns not to charge in a gas tight container.
Now I know that the OP (sorry for the hijack, BTW) wasn’t likely to build a gas tight container, but better safe than sorry, right?
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [January 11, 2013, 11:39pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/26 "2013-01-11T23:39:59Z")
> [@dexter](#):
>
> Dang. Beowulff, I know you are going to think I’m trying start something, but I’m not. I consider you a knowledgeable and very helpful poster. But I happened to have a used sealed lead acid battery sitting behind my computer desk, and we are supposed to fight ignorance, right?
>
> I don’t know if it is AGM or not, but it does say it is sealed lead acid, and nonspillable. Along with warnings not to incinerate or short the leads, it warns not to charge in a gas tight container.
>
> Now I know that the OP (sorry for the hijack, BTW) wasn’t likely to build a gas tight container, but better safe than sorry, right?
That’s probably a reasonable precaution, in case of accidental overcharging. Still, I doubt whether any container that has holes for cables to exit can be considered “gas tight.” Out of an over-abundance of caution, he could drill a few holes at the top.
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### Author:  [@Michael63129](https://boards.straightdope.com/u/Michael63129)
#### Post date: [January 11, 2013, 11:42pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/27 "2013-01-11T23:42:53Z")
> [@PatriotGrrrl](#):
>
> That’s old school thinking. Many monitors nowadays use a laptop-like power supply brick and thus have a standard DC input. The one I’m using now is 12V 3A.
Some monitors may have an external power brick, but I still see many that don’t, including new ones.
ETA: Also, even if it does have a 12 volt input, you may not be able to just connect it to an unregulated battery and expect it to work, depending on the circuitry inside (there will be a regulator for the logic, but maybe not for the power stuff, since if the input is normally regulated, there is no need for regulation; battery voltage may range a couple volts higher/lower than 12 volts).
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [January 11, 2013, 11:47pm UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/28 "2013-01-11T23:47:35Z")
> [@PatriotGrrrl](#):
>
> Many monitors nowadays use a laptop-like power supply brick and thus have a standard DC input. The one I’m using now is 12V 3A.
I haven’t seen monitors with power bricks in a while. My 4 newest monitors (ASUS, Dell, HP and Samsung) all have built-in power supplies - i.e. AC power cord plugs directly into the monitor.
Anyway, if battery weight isn’t a major concern, I would use a 12V-\>120V inverter and accept the somewhat lower energy efficiency.
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### Author:  [@Khendrask](https://boards.straightdope.com/u/Khendrask)
#### Post date: [January 14, 2013, 11:00am UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/29 "2013-01-14T11:00:25Z")
/shrug… I’d go with a direct 12V (or 24V) solution. Direct from battery to the devices. You might need a regulator for the video receiver, or not, depending on what one you get.
I’m in a manufacturing plant, and our standard for the past 5 years or so is to run all 24VDC computers, monitors, switches, etc on 24VDC only.
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### Author:  [@Dog80](https://boards.straightdope.com/u/Dog80)
#### Post date: [January 14, 2013, 11:43am UTC](https://boards.straightdope.com/t/electrical-engineers-electronics-experts-i-need-assistance/646896/30 "2013-01-14T11:43:18Z")
The problem with some cheap inverters is that they draw a substantial current from the battery even when they are not powering anything on the AC side.
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