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Thick cables for UPS


gallderhen
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Hi again

 

So my brother wants to hook up his 24V 2000VA UPS to a pair of 12V 18Ah batteries, but the batteries dont fit in the UPS case. He's decided to put it next to the UPS in a plastic container, running the cables through the side of the UPS.

 

Now the Question: An electrical friend of mine can give me 3m of 15mm welding cabling and 16x6mm lugs with heatshrink to match. Will the cable work for connecting the batteries to the UPS if I connect the UPS cables to these welding cables using Brad Harrison 50amp plugs?

 

 

-G-

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2 hours ago, gallderhen said:

Question: An electrical friend of mine can give me 3m of 15mm welding cabling and 16x6mm lugs with heatshrink to match

 

2 hours ago, gallderhen said:

Brad Harrison 50amp plugs?

25mm would have been better. Please remember, at full load the current draw on the DC side would be appr 83 amps. Much higher than the 50 amp rating of the Brad Harrison plug. If you manage your loads, the 16 would be okay. 

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12 minutes ago, Jaco de Jongh said:

 

25mm would have been better. Please remember, at full load the current draw on the DC side would be appr 83 amps. Much higher than the 50 amp rating of the Brad Harrison plug. If you manage your loads, the 16 would be okay. 

18ah battery wont even come close to the 83 amps 

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3 hours ago, scrarfussi said:

18ah battery wont even come close to the 83 amps

May I ask why you say so? The Ups came out with 7ah batteries, and I suspect they were able to supply the rated power for a short time......

The cable size should never be determined by the Battery size, the correct way is to size it for the max load the inverter can draw from the battery. 

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42 minutes ago, Jaco de Jongh said:

May I ask why you say so? The Ups came out with 7ah batteries, and I suspect they were able to supply the rated power for a short time......

The cable size should never be determined by the Battery size, the correct way is to size it for the max load the inverter can draw from the battery. 

(I am assuming this is an RCT/Mecer 2000VA UPS or similar)

 

Well, those batteries that came with the UPS is pretty special - the Yuasa NPW45-12. It is capable of delivering 600W for 10 minutes. I don't think the replacement 18Ah would be able to do that, but they surely will be able to deliver 85A for short periods.

The inverter on the other hand will not be able to deliver close to 2000VA for an extended period. It will likely do up to 800W for a short period (actually 800W is the figure written on the PCB).

If you are using it to power a small load, keep in mind that it's self-consumption is about 25W.

Honestly I can not understand how these are sold so cheap. You can not buy the batteries in SA for the price of the UPS (specifically the NPW45-12 - even on Amazon), and then you also get a free transformer. If someone would just go to the trouble of designing a swap-out control board that turns it into a pure sine with proper charge capabilities, you would have a winner.

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On 2020/02/29 at 4:51 PM, P1000 said:

Yuasa

They've always made some nice stuff. I remember 20 years ago, in high school, I had a small Yuasa brick that powered my cassette player (through a LM317T linear regulator), cause we were not allowed to use the AC plugs in the hostel. To steal electricity for your radio was (om krag te tap) was something a few guys did, but a rechargeable battery (that could be recharged in the ironing room overnight) was a much safer option (for your backside).

Man... I know this is off topic... but I have to tell this story. So... edit... here goes. One weekend me and another guy called David got bored and we screwed open a few light switches, and noticed there's three red wires in there. So one of them clearly goes to the light, since that is attached to the OTHER side of the switch... but why is there two red wires on the supply side? A few minutes later we figured it out... it loops over to the next room... so what do we do? Of course, we move the wire over so that this switch turns off the lights in all the rooms downstream. And of course this is very funny.

A few hours later we modify another room, so now half the top floor has some electrical... uhm... quirks. But of course the people in the downstream rooms don't like it, and within the hour we're hauled down to the office of the "koshuisvader". That evening my parents got called AND I got the largest hiding of my school career. And then the funniest thing happened: We got sent back to FIX what we changed! No, they did not call an electrician. We were trusted sufficiently to undo our naughty rewiring.

🙂

Edited by plonkster
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7 hours ago, plonkster said:

Man... I know this is off topic... but I have to tell this story. So... edit... here goes. One weekend me and another guy called David got bored and we screwed open a few light switches, and noticed there's three red wires in there. So one of them clearly goes to the light, since that is attached to the OTHER side of the switch... but why is there two red wires on the supply side? A few minutes later we figured it out... it loops over to the next room... so what do we do? Of course, we move the wire over so that this switch turns off the lights in all the rooms downstream. And of course this is very funny.

Let me guess: That you didn't find the DB and isolate the supply first..

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38 minutes ago, Richard Mackay said:

Let me guess: That you didn't find the DB and isolate the supply first..

We did... we weren't quite THAT stupid 🙂

It's also interesting how this story grew "tails" as we say in Afrikaans. My sister tells everyone I got back at a Bully by rewiring his lights, so recently I unfortunately had to correct her and tell her there was no ultimate victory in the story... I was just a naughty kid! (I was 15 at the time).

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So the cables worked out very well. Hooked up everything last night to check that it all works.

Tomorrow I'll put the batteries in a ventilated plastic box next to the UPS. Wouldn't say its up to an electricians' standard, but not too bad 🙂

PS Gonna get some red and black tape or markings to mark the positive and negative (the shop only had the green welding wire)

 

d6787c8a-80d3-4b4e-9f9d-40090724af4a.jpg

Edited by gallderhen
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On 2020/03/06 at 9:29 PM, gallderhen said:

So the cables worked out very well. Hooked up everything last night to check that it all works.

Tomorrow I'll put the batteries in a ventilated plastic box next to the UPS. Wouldn't say its up to an electricians' standard, but not too bad 🙂

PS Gonna get some red and black tape or markings to mark the positive and negative (the shop only had the green welding wire)

 

d6787c8a-80d3-4b4e-9f9d-40090724af4a.jpg

Actually I think it is pretty good.  You clearly haven't seen most electrician's work.  You don't really need to worry too much about putting this in a container except to prevent people from messing with it.  These batteries you bought are pretty much sealed and being open you would be able to see if they start bulging, etc.  My only gripe would be to reduce that wire length between the two batteries with the fuses.

 

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