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Running off 24 volts


nirvana
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Can I run a 24v DC PSU direct off a pair of 12v deep cycle batteries wired to give 24v?

ie one of these to power a full blown PC.......I'll stick a fuse inline but apart from that is it safe?

Actually I could do with some sort of '24v wall sockets' to run other stuff too, any ideas?

130w08.jpg

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I'm a bit vague on the question. Certainly 2x12=24. Why would you want your PC to run on 24 V? Are you a trucker?

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34 minutes ago, MrPin said:

Why would you want your PC to run on 24 V? Are you a trucker?

 A PC motherboard runs at 12v, why would you want to run it off 240v? :P

I run my PC off a 20v laptop power supply....

i'm gonna buy some solar panels and use them to charge up some mofo batteries connected up in 24v........so I'm just really interested in the 'safety aspect' of taking power direct and should you use a 'voltage regulator' but I can't see the voltage needing much regulating like that stuff that comes out of 240v AC o.O

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It depends on the PSU.  I'd imagine it was designed to run from a switched-mode 240v power supply, thus fairly well regulated to 24v.

Standard 12V batteries would be about 12.6v, so 25v.  That'll almost certainly be no problem at all.

When charging  (ie, from your solar supply) 12V batteries receive between about 13.6v (slow/float charge) and 14.5v (a bit aggressive fast charge) -- so 27v to 29v.  Would this be an issue?  Probably not...  (I'd say any decently designed power supply would be happy with this supply voltage range, but I'd prefer to look at a manufacturer's tech docs before plugging into anything too expensive).

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12 minutes ago, dgul said:

It depends on the PSU

well it's not a PSU as such (i've always referred to it as a DC-DC converter board)

if you look at the pic up top it's running off a 'laptop PSU'

this is the spec https://www.winmate.com.tw/PowerUnit/PowerUnitSpec.asp?Prod=07_0006&Typeid=B0108070404

apparently you can stick 2 together and get up to 240watts....

so would you stick a fuse inline?

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50 minutes ago, 5min OCD speculator said:

well it's not a PSU as such (i've always referred to it as a DC-DC converter board)

if you look at the pic up top it's running off a 'laptop PSU'

this is the spec https://www.winmate.com.tw/PowerUnit/PowerUnitSpec.asp?Prod=07_0006&Typeid=B0108070404

apparently you can stick 2 together and get up to 240watts....

so would you stick a fuse inline?

Always use a fuse.

They claim load regulation for +/-10%, so 21v-27v or so is definitely in spec.  If you had a 'gentle' charge you'd not go beyond that -- so that would be fine.  It looks to be decently made, so 30v probably wouldn't kill it (although the load voltages might go out of range -- they don't say that they won't...)

re. connecting two together -- It is almost certainly using a switch mode approach and as a general rule you should never combine two (or more) SMPS together.  You can if you like and you might even get away with it for quite a while, but it isn't a simple case of 'twice the power' and there are certain 'gotchas' if you don't do it properly (whatever that means).  It is always better to just use a larger power supply if you need the additional power.

[and it is a PSU, just not a mains electricity one]

Edited by dgul
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21 minutes ago, dgul said:

It looks to be decently made, so 30v probably wouldn't kill it

Scenario: I have 2x 12v deep cycle 100aH batteries in series that are at 13.6v each fully charged but still connected to a 'quality' victron solar charge controller....

Something pulling power out them won't be able to exceed 27.2v right?

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1 hour ago, 5min OCD speculator said:

Scenario: I have 2x 12v deep cycle 100aH batteries in series that are at 13.6v each fully charged but still connected to a 'quality' victron solar charge controller....

Something pulling power out them won't be able to exceed 27.2v right?

They won't be 13.6v fully charged.  Well, maybe immediately after charging, but it'll fall very quickly (few minutes) to the normal 'full' voltage of 12.6-12.8v or so.

The charge controller will offer 'more volts' for charging (otherwise how would the 'electricity get into the battery'?).  So, if you've got the load connected 'in parallel' while charging then you'll see more volts across your load.  How much more depends on the charge controller design.  13.6 would be a fair minimum, I'd guess -- 13.6v is a float charge for lead-acid (and probably why you'll be reading 13.6v for 'fully charged').  I'd imagine it'll readily get to 14.1v, and could get to 14.4v depending on design (which itself will depend on how much power is available from the solar array).  Much more than that is unlikely.

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1 hour ago, 5min OCD speculator said:

Scenario: I have 2x 12v deep cycle 100aH batteries in series that are at 13.6v each fully charged but still connected to a 'quality' victron solar charge controller....

Something pulling power out them won't be able to exceed 27.2v right?

Definitely need a charge controller as panels alone will float to much higher voltages than their nominal. Besides a good MPPT charge will get the best power out of the panels.

Looking here it states that working voltage range for the PSU is18V to 28V, so assuming theVictron is programmable then setting the max charge voltage should do the trick.

Also in this data sheet states working current at stated voltages, so depending on how deep you want to discharge your batteries then that is a guide to fusing required.  Ideally you'd have a cutoff or alarm to prevent over-discharge of your batteries that is the only way to prevent damaging them by doing so. Unless of course the power supply has a cutoff, bit even then at 18V input you are already seriously over-discharging lead acid - ideally you don't want to be dropping them to less than about 11.5V  

18V~28V allowable, 8A~5A

https://silentpcreview.com/winmate-dd-24ax-dc-dc-module-for-silent-efficient-power/

 

 

Screen Shot 2021-01-12 at 15.29.24.png

Edited by onlyme
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4 hours ago, 5min OCD speculator said:

Can I run a 24v DC PSU direct off a pair of 12v deep cycle batteries wired to give 24v?

ie one of these to power a full blown PC.......I'll stick a fuse inline but apart from that is it safe?

Actually I could do with some sort of '24v wall sockets' to run other stuff too, any ideas?

 

Neutrik make some very nice high quality connectors - low and high voltage, plus high powered speaker connectors.  If you are going down the route of having multiple devices then you absolutely must have some form of discharge controller to prevent over discharging your battery bank.

Cheapo junk end but will probably work, better than nothing.

https://www.ebay.co.uk/itm/Battery-Anti-Over-Discharge-12V-24V-36V-48V-Low-Voltage-Alarm-Protection-Board/402641635330?hash=item5dbf4fc802:g:W2gAAOSwULpf~CPJ

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20 minutes ago, onlyme said:

If you are going down the route of having multiple devices then you absolutely must have some form of discharge controller to prevent over discharging your battery bank

yeah good point, how about I just have some bluetooth device connected across the battery bank monitoring voltage?

then if it drops below 11.5v say it sends an alarm to home assistant? ooh that sounds super duper techy! :Jumping:

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6 minutes ago, 5min OCD speculator said:

yeah good point, how about I just have some bluetooth device connected across the battery bank monitoring voltage?

then if it drops below 11.5v say it sends an alarm to home assistant? ooh that sounds super duper techy! :Jumping:

Better automatic, just in case you miss the message.The 240V inverter might have/will likely have an audible alarm for low input voltage as well. Doesn't mean you shouldn't be monitoring the voltage anyway - both battery bank and panel output as not much more effort. Redundancy is good.

 

One of the local scrappies I can get decent car batteries for a tenner a pop. I know they are not exactly deep cycle but 10 of those at £100 gives you a lot of redundancy and spare capacity regardless if some of them area bit duff - they do use a high current tester to check them out.  

Bimble solar do some pretty cheap used panels.

If you have the space consider going large and cheap.

 

Edited by onlyme
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2 hours ago, onlyme said:

If you have the space consider going large and cheap

Interesting you should say that, cheap is my middle name! :)

Been speaking to a geezer and he says just get big mofo batteries, 24v solar panels and charge the batteries direct. MPPT is not needed if you know you're not in danger of overcharging your batteries, hmmm

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Holy shit overlanders are go! This guy is cool and I need to start developing some Blynk stuff now methinks :Jumping:

 

 

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43 minutes ago, 5min OCD speculator said:

Interesting you should say that, cheap is my middle name! :)

Been speaking to a geezer and he says just get big mofo batteries, 24v solar panels and charge the batteries direct. MPPT is not needed if you know you're not in danger of overcharging your batteries, hmmm

Just check the max open circuit vintage for each of the panels in that cased be shore you don't have anything sensitive downstream that can be affected by over voltage.  I would still see if you can get a deal on a decent sized MPPT, Bimble do those as well S/H IIRC, it should improve the efficiency by a fair amount. 

I suppose you could have an over-voltage device that dumps power when voltage dries up to 28V, bit that could be a little specialist / pricey or need home brew.

BTW you need blocking diodes if connecting direct to prevent the solar panels draining the batteries at night, some panels come with them already most don't though as intended to work with charge controllers.

Edited by onlyme
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1 minute ago, onlyme said:

Bimble

I'm behind enemy lines ;) but it's fecking freezing.......some geezer is selling a flexy panel which I could chuck in the back of the car but the miserable froggy fecker won't send it.....

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50 minutes ago, 5min OCD speculator said:

Interesting you should say that, cheap is my middle name! :)

Been speaking to a geezer and he says just get big mofo batteries, 24v solar panels and charge the batteries direct. MPPT is not needed if you know you're not in danger of overcharging your batteries, hmmm

If the voltage from the panels is a good match for the battery voltage there is not much advantage to be had from MPPT. Although MPPT will give you greater flexibility on your panel choice, i.e. higher voltage panels are not an issue. Also gives the option to put panels in series for higher voltage (and less losses in the wiring) also check on the max voltage input for an MPPT controller. I have an EP Solar tracer one that form memory is good for up to 150v input.

£59 inc VAT for a 250w panel if you are near enough to collect from these guys (note these are poly panels):

https://www.bimblesolar.com/solar/used-solar-panels/250w-bisol-used-solar-panel

If you can't collect the delivery cost may kill it as sometimes these places insist on pallet delivery.

 

Don't skimp on the wiring, keep it chunky. Fuse accordingly to protect the wiring. In past I've managed to pick some bagain reels of tr-rated wire in odd colours, buy a few packs of red and black shrink tube.

 

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1 minute ago, 5min OCD speculator said:

@invalidthanks for the info, bimble are too far away ;)

what do you think of these panels? https://www.leboncoin.fr/bricolage/1908067864.htm

where do you buy your wire from? I was told you keep the voltage up as much as poss to avoid having to use thick wire which is obviously not cheap....

Yeah, they look good. No experience with Benq but its a name I've heard of so a good start. Note being a more modern larger panel the VOC is quite high (relatively).

For wire (in the Uk) I've used Ebay or TLC. I've used single core in places where the cable doesn't need to flex:

https://www.tlc-direct.co.uk/Main_Index/Cable_Index/Singles_1/index.html

On one of my systems I used doubled up 10mm to go from the controllers to the batteries, the max that goes through them is around 70 amps (at 12v, how I regret not going 24v from day one...). They sometimes get a little bit warm where they go into the breakers. Note - most hager breakers are rated for DC less than 60v if you derate slightly. Beware cheap auto fuses from ebay, most are complete crap. Go for littl(sp?) fuses. Also, a lot of people think, for example a 20A fuse will blow at 20A - they don't.

 

A 24v system will be half the Amps of a 12v system for a given wattage. Low voltage DC stuff can pull lots of amps and wires and fuses can get rather warm. Good quality connections are important. Check any screw down terminals for tightness every once in a while. Every once in a while I run my hand over everything to check for anything that might be getting hot. In my early days I melted quite a few fuses and choc blocks.

Voltage drop calculator to give you and idea of what wire sizes you will need:

http://www.calculator.net/voltage-drop-calculator.html

 

This is just something I have done as a hobby for the last 15 years or so, I'm not an electrician and have made many mistakes along the way. Learn from my mistakes but usual caveats about its dangerous (mainly fire risk), only do what you are happy with etc.

 

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55 minutes ago, invalid said:

70 amps

wooo that's a lot of amps....I actually redid the leccy here myself and 'bodged' my way through with Hager breakers :)

So have you set up a 'DC fuseboard'? Can I get away with 16mm cable with 24v?

Thanks!

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3 hours ago, 5min OCD speculator said:

@invalidthanks for the info, bimble are too far away ;)

what do you think of these panels? https://www.leboncoin.fr/bricolage/1908067864.htm

where do you buy your wire from? I was told you keep the voltage up as much as poss to avoid having to use thick wire which is obviously not cheap....

Very high output panels, look pretty top notch. 200W more the norm.

Are you sure you want a DC circuit at all? If you do want considerable levels of power then as mentioned your cabling will become somewhat of a headache, what so you want to run?

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5 minutes ago, onlyme said:

Very high output panels, look pretty top notch. 200W more the norm.

Are you sure you want a DC circuit at all? If you do want considerable levels of power then as mentioned your cabling will become somewhat of a headache, what so you want to run?

Good point, might be easier/cheaper to grid tie it:

https://www.aliexpress.com/item/1005001424339166.html?spm=a2g0o.productlist.0.0.74e66052e4LgUF&algo_pvid=8b067195-418d-4e77-8e41-983244eb4cb8&algo_expid=8b067195-418d-4e77-8e41-983244eb4cb8-0&btsid=0b0a050b16104947773994464eccea&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

 

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2 hours ago, 5min OCD speculator said:

wooo that's a lot of amps....I actually redid the leccy here myself and 'bodged' my way through with Hager breakers :)

So have you set up a 'DC fuseboard'? Can I get away with 16mm cable with 24v?

Thanks!

70 amps at 12v is a lot of amps but not a lot of power!

As its a hobby system its something that has grown over time, if I started from scratch I would do it differently. 24v as a minimum for off grid with batteries.

And then the batteries and maintenance of is a whole new thread....

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4 minutes ago, invalid said:

70 amps at 12v is a lot of amps but not a lot of power!

As its a hobby system its something that has grown over time, if I started from scratch I would do it differently. 24v as a minimum for off grid with batteries.

And then the batteries and maintenance of is a whole new thread....

Check out these puppies, 2V 1000ah power station batteries.

https://www.bidspotter.co.uk/en-gb/auction-catalogues/eddisons/catalogue-id-eddiso10925/lot-a7085ba4-8a10-47b7-98a0-ac9900eb3440

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