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Author Topic: Can two 36v power supplies be used in series to get 72v?  (Read 28330 times)

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Offline simpson36

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #60 on: May 04, 2009, 06:31:10 AM »
Jeff:

I'll pass along what info I have collected on this issue that may be helpfull to you.

The 36V 8.8A PS sells for $60 on Keling. The equivalent Mean Well is $140 from electronics suppliers.

The transitors that cooked are FUJI  2SC3320  sell for under $5 each - cannot find specs

Replacement per NTE cross ref is  NTE2311      sell for over $16 each from the same supplier.

The significant spec on the NTE2311 is 15 amp. (data sheet avail from NTE if you need more specs)

With a $22 delta in just that one component of a $60 product, it is easy to speculate how Keling keeps the cost down.

These are the pair of high speed switching transistors on the back edge of the board, heat sinked to the case.

Question: Which transistors are in the Mean Well?


I am replacing the rectifier, voltage regulator and silicon diode with equivalent parts . .  just 'cause.

Hope this info is useful.


NoSmoking:

Schematic?









Offline simpson36

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #61 on: May 04, 2009, 06:40:14 AM »
While I have the guru's attention, here is another power supply question:

My new 72V unregulated dual rectifier 20A toriodal tranformer power supply is claimed to have significant overload capability, but it does not seem to perform that way.

I have 3 steppers limited by their Gecko drives at @3A each and a servo at 7A continuous that can pull as much as 40A, but the Gecko drive limits it to 20A max.

If the servo starts too quickly the stepper will stall and vice versa, so I'm not getting the overload capacity I thought I would have.

Which component do I upgrade to increase the overload capacity?


Offline Jeff_Birt

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #62 on: May 04, 2009, 12:31:15 PM »
Speaking frankly, and not to knock anyone, I think the Keling power supplies are MeanWell knock offs. I have tried and tried to get data sheets for the power supplies from them to no avail. I don't think you would have fried a true MeanWell supply that way.

Unregulated supplies are just that, unregulated. The more current they supply the lower the output voltage is. When your servo starts and hogs a bunch of current the voltage is going to drop way down. To prevent sags all you can do is use a bigger supply, add more filter capacitors or not drive the servo as hard.
Happy machining , Jeff Birt
 

Offline simpson36

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #63 on: May 05, 2009, 04:21:20 AM »
Well. my replacements for the rest of the chips in the 36v supply will arrive today. If that fixes it, fine , otherwise, it goes in the trash.

The annoying thin about the Keling is that they make this claim:

A:  Stepper Motor Driver Power Supply Specifications:

1: High Efficiency, Low Temperature, Small Size.
2: Over Load and Short Circuit Protection.
3: Over Voltage Protection.
4: Input: 120VAC or 220V


I was abusing it, no doubt about that, but I expected the worst to happen would be a trip or blown fuse.

If one was to buy the $60 Keling unit and immediately install a pair of transistors @ $32 and the other chips at about $9, you now have a $101 power supply and you are out the time to swap chips and have obviously voided any warranty. I think I would sooner shop around for the best price on a Mean Well or equiv.




I understand that unregulated means the voltage drops, but it seems incredible to me that a 20A power supply (that claims huge overload capacity) can start with 72V and drop so far with a max draw of 29A that it cannot keep a 4V stepper going.

The PS has dual rectifiers. Does that mean 10A per rectifier, or will either supply the total 20A? Can the rectifier limit current?
 

40A max draw on this NEMA34 servo seems like a formidable hit.  Imagining 3 or 4 of these pulling juice at the same time is kinda scary  :o
Re: Can two 36v power supplies be used in series to get 72v?
« Reply #64 on: May 05, 2009, 10:26:26 AM »
There is a couple of things you can check if you suspect voltage collapse, if the load is sustained long enough to obtain a reading, first check the AC in to the bridge to see how far it drops, if at all, if the voltage drops substantially, then the transformer characteristics cannot sustain the load and apart from changing the transformer there is not much you can do, if the AC remains fairly constant, then it would be the DC ripple is increasing due to the load.
An increase in capacitance may help, but as you increase the Capacitance the VA requirement of the Toroid goes up, so if you were to have sustained high load, you may see transformer heating.
I will forward the circuit via mail.
N. 

Offline Jeff_Birt

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #65 on: May 06, 2009, 01:11:17 PM »
I have been using the MeanWell S-320-48 for smaller machine but I was testing a MeanWell SP-320-48 yesterday as it has a universal input, and power factor correction and is CE approved. It was solid as a rock. One hour at 80-85% load and the built in fan kept the case cool. I could not overload it with the types of steppers I would use on such a system so I directly shorted the output. The supply shut right off and started again when the short was removed (just like the data sheet says).

A good quality switching supply with proper overload protection is hard to kill.
Happy machining , Jeff Birt
 

Offline simpson36

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #66 on: May 06, 2009, 01:40:56 PM »
Just to finish up this story, I received the rest of the replacement chips yesterday and installed them in the fried 36V Keling Switching PS

No joy.

So, I sniffed around the area with an ohm meter where the power transisitors left their scorch marks and I found there was a resistor and a diode that got cooked along with the switching transistors. 
Replaced those and Viola! Up and running again.

Theoretically I have replaced the weak links with better quality componenets and now have a reliable PS.


I don't have the courage, frankly, to short the output as a final test  :-\


NoSmoking; got the schematic, thanks.

Offline simpson36

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Re: Can two 36v power supplies be used in series to get 72v?
« Reply #67 on: May 09, 2009, 07:28:55 AM »
Another update:

My repaired switching power supply put out two amps for a few minutes and the more fireworks. It is now in the trash and I just kept the nice aluminum case to put Geckos or a speed controller in someday perhaps.


Anyway, I found what will hopefully be a permanent solution to the delema. I found a fellow who will make up an unregulated power supply for me that can be switched back and forth from 38V to 76V. You have to contact him and ask for what you want as his listed PS do not automatically have this feature. He did not charge extra to custom build a PS the way I need it. Hopefully this will be the end of the drama.


http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370197063676&ssPageName=ADME:X:AAQ:US:1123





Re: Can two 36v power supplies be used in series to get 72v?
« Reply #68 on: June 09, 2009, 01:57:23 PM »
I have been buying my Toroidal's from him for some time, apparently he builds these transformers also.
They are easy to tack on an auxiliary winding if you find you need it, 5v,12, 24v etc.
Nosmo