 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : Anyone interested in a new MM+ backpack design?
  Page 3 of 3 |
|||||
| Author | Message | ||||
Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 5710 |
I've just found this: https://uk.farnell.com/murata-power-solutions/oki-78sr-5-1-5-w36-c/converter-dc-dc-1-o-p-7-5w-1-5a/dp/2102101?MER=bn_browse_1TP_MostPopular_3 A very neat little switching regulator module. 7-36VDC in / 5V 1.5A out without a heatsink and remarkably cheap. Pin compatible with 78xx series (and not all that much bigger). 3.3V version also available. "Gut feeling is that the SSRs won't even get warm to the touch." I've come across that too. Sometimes power handling can be very deceptive. If it was me doing this I'd certainly get one and try it on the different pumps. There's nothing like empirical evidence. :) Edited 2019-11-26 00:17 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
||||
| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
These guys have a HUGE range. Even 3-output such as 3v3 with +12v/-12v CUI at Digikey |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3505 |
Hi Tinine / Mixtel90 Just some advise when choosing a DC-DC convertor. Choose one that comes relatively close in power to what you need. Typically these convertors do pulsewidth modulation of the power switch. But they have a limited range over what they can vary the pulsewidth. So if you have a convertor running at half power, or full power it will run at it's designed frequency, modulating the powerfet pulse width. But if you are at low power loads, the pulsewidth becomes so narrow it goes out of control, and the switchers start skipping pulses (per design, this is not a fault). So in stead of 500kHz they could run at 50kHz. And that causes significantly higher ripple. I have such a switcher on my desk that has 19mV ripple at full load, and 200mV at 10% load. And it can only be cured by adding significant capacitance at the 5V output. This is why in your design a 0.5A switcher may perform better than a 1.5A switcher. That is also why I suggested to power the 3.3V for the microprocessor from a linear regulator from the 5V. The 3.3V uses not much current (50-100mA) and may be sensitive to noise (ADC channels, PLL's inside the micro). Regards, Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5710 |
In this instance I already have the 5v-3.3v linear reg on the 01 board, local to the micro. The 02 reg only converts 24v (plus or minus a bit) to 5v. That's what's feeding the 01 up the ribbon cable. I don't know what current I'm looking at yet as I've not built an 01 board. :D Most of the bits have arrived now. It's basically a MM+ 64 backpack with the 2.8" display. Not a lot more than that really. I suspect that the variation in backlight level would probably be the biggest load change on a switcher. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
||||
| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
This is good, timely information. I am using +/-12v from a switcher for my PWM-Opamp DAC. I suspect that I have ripple (didn't have my scope) but not sure if it's from the PWM or the switcher. The DAC output is +/-10v and feeds a high impedance input. I was going to start by substituting batteries for the +/-12v. Thanks, V Regards, Craig |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3505 |
The PWM ripple after the low pass filter you can easily simulate in spice or similar (I use Simetrix, the demo version is free). If you look at the Huntron Tracker schematics you can see a 3 stage low pass filter for use with a 100kHz PWM. Schematics Backpack Tracker Edited 2019-11-26 19:13 by Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
@Mixtel90 -- Sorry to hijack your thread. I was surprised by the specs and the price for the CPC1998. I like your idea of putting a red led in series with the gate to provide an indication of operation! In an attempt to isolate the micro board from 120 vac circuits I immediately visualized a tiny PCB with one CPC1998 enclosed in a galvanized electrical junction box mounted near each pump with a separate 120 vac feed in Greenfield armor feeding each junction box and pump and clamping or cementing the CPC1998 inside to the box interior. UL Junction Boxes These boxes would have a surface area of at least 40 sq in (260 sq cm ???) with the cover. I suspect that this surface area would be more than adequate to cool the junction. With 6 to 10 junction boxes separately mounted on each pump there would be no mutual heat concentration. @Tinine -- I particularly like the optically isolated input and zero crossing behavior which you reference. I have not been able to find a source for the Kunze KU 1-59 heat sink, the phase change interface material KU-ALC 5 and the transistor clip KU 4-499/1. I think you're right that they won't even get warm to the touch. @Volhout -- The ambient temperature down there in my cellar will vary from about 5°C to 38°C seasonally. Thanks for posting the graph from the Ixys spec sheet.  But now, back to the previously scheduled program. Switching regulators can definitely throw a monkey wrench into the works. A few decades ago I attempted to use a swicher to replace a linear regulator feeding an automated test setup for the B747 Delco INS computer. When it was lightly loaded the on duration became so short and the ripple voltage so high that the INS computer under test would reboot ... OOPS ... back to square one. Paul in NY |
||||
CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1985 |
the CPC1998 (with ZC det so no probs switching mains) is quite an expensive part in small quantities. I use Omron G3MB-202P a lot. It is an older part and will only switch 2A@240V but is available in large quantities, at a variety of LED voltages and you can snag them from fleabay for as cheap as 10off for £7.60. probably much cheaper if you hunt around. So depending on the spec, you are getting almost 10:1 price difference. I use tons of them for switching mains lights and have yet to find a dud. jus' sayin' Edited 2019-11-28 04:08 by CaptainBoing |
||||
| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
I love threads like this...exchanging real-world experiences/findings  |
||||
| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
Hi Andrew, thanks for looking but the G3MB series is obsolete and the newer G3MC price is up in the same region as the CPC1998. In this application the unit cost is not the controlling factor. Since the pumps and their wiring are not very accessible and reliability is paramount I think I will stick with the newer part with the higher current rating. The CPC1998 will be replacing much more expensive mechanical relays and will probably be very satisfactory if I can keep them cool. Paul in NY |
||||
| Page 3 of 3 |
|||||
 Print this page |
