Thread: New start
-
02-04-2018 #321
-
02-04-2018 #322
-
02-04-2018 #323
-
03-04-2018 #324
New day and new questions :D
I fused my 24v psu with a 2A fuse.
But now that I think about it.. must be wrong?
The psu is 24v / 2A but thats on the secondary side.
Input is 50w so fuse should be around 0.25A.. correct?
My toroid is 500VA so without inrushcurrent 2.2A fuse should be enough? I fused 2.3A but that kept blowing every 5-7times I powered up. Exchanged for a 3A and now it seems okey but is it still protected?
I'm wanting to exchange to MCB type of fuses. Now I have 5x20 glassfuses. Not really easy to find MCB with these kind of ratings :)
Skickat från min SM-G955F via Tapatalk
-
03-04-2018 #325
Re. 24V PSU - you're broadly correct - though personally I'd give it a little more headroom (rough rule-of-thumb is 125%) - probably 300mA, and with a power-supply then use an anti-surge or time-delay fuse.
For the toroidal transformer an anti-surge is a must, though I'd* even go as far as installing a NTC thermistor in series with the primary coil to limit the inrush current.
* wrong tense : I'm building up a PSU now for my next machine - NTC thermistors on order, SSRs on order - in the mistaken belief that zero-crossing would be a good thing - but a little googling reveals the role of the NTCs.
-
03-04-2018 #326
-
03-04-2018 #327
I have NTC on my transformer was a bitch to get the right one. I have no issues running it without NTC (Doesn't trip anything) but the real advantage for me is I can use a MCB type a if you use NTC for extra protection, remember I blew a transformer up already lol.
We're 99% certain we plugged the bridge rectifier in back to front during testing but you're not using one are you?
I have a 1kva transformer 45v output (70v when rectified)Last edited by Desertboy; 03-04-2018 at 08:40 AM.
http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm
If you didn't buy it from China the company you bought it from did ;)
-
03-04-2018 #328
Why wouldn't you just use ready made inrush current limiter?
I am using Block ESG3 limiter with my 625VA transformer..works great.
-
03-04-2018 #329
For the 24V supply, a couple amp fuse should be fine. Some of the better supplies have recommended input fuse ratings, and from memory they're typically in the 1-2A range.
The thing with switch mode supplies, is due to their inherent design/failure modes, the smallest possible fuse is unlikely to prevent damage to the supply. Any reasonable quality supply will have the output overload protected anyway, plus they also cause a surge on power up, so too small fuse is more likely to cause more problems than it will prevent. The fuse is only their to prevent fires should something short out internally, by which time the supply is dead anyway.
I wouldn't personally bother with any anti-surge on a toiroid that size, unless it's causing problems. Toiroids are however where correct size fusing is the difference between just blowing a fuse, or melting the toiroid should you overload it.
If I did want to add some anti-surge, I'd fit a NTC thermistor, and parallel it with a relay that bypasses the thermistor after a couple seconds. The problem with just a thermistor on it's own, is it relies on current passing through it to keep it warm and resistance low, so when everything is sitting idle, it can cause the voltage to drop.
The problem with thermistors on their own, is if you use too large a one, the voltage drop will be larger, and if you use too small a one, you risk burning it out under heavy load.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
-
03-04-2018 #330
Thread Information
Users Browsing this Thread
There are currently 5 users browsing this thread. (0 members and 5 guests)
Similar Threads
-
NEW MEMBER: We all need to start somewhere!
By Realtime in forum New Member IntroductionsReplies: 0Last Post: 16-05-2017, 08:43 PM -
NEW MEMBER: A new start for me.......
By Nthkentman in forum New Member IntroductionsReplies: 4Last Post: 23-08-2014, 10:50 AM -
Where to start?
By Inquisitor in forum Gantry/Router Machines & BuildingReplies: 7Last Post: 27-11-2012, 02:35 PM -
where to start
By martin54 in forum Gantry/Router Machines & BuildingReplies: 16Last Post: 22-09-2012, 11:29 AM -
is this 2.5d where do i start? help please if you can
By h4ppy-chris in forum General DiscussionReplies: 4Last Post: 29-03-2011, 12:21 PM
Bookmarks