Rechargeable power supply from Stanford Research Systems - Page 1
Forum section: electronics / general

author: Pat Pending
author_rank: Regular Contributor
timestamp: April 20, 2012, 05:46:43 am
content: I was clearing out a hoard of trade related magazines that had piled up, when this ad from SRS (March 2011) caught my eye.Oddly enough, it's for an Ni-cad powered Isolated Voltage Source SIM928. Unlike Dave's PSU, this one is rated for a mere 10mA @ 20Vand appears tethered to a larger system rack.http://www.thinksrs.com/products/SIM928.htm...on that thought, is there an abbreviation for a battery powered PSU (BPPSU) or portable PSU (PPSU) anyway?If two legs were added to the portable PSU, you'd have yer'self a Star Wars GNK Power Droid.For inexplicable reasons, these made ...GONK...GONK sounds and that to me, sounds like the perfect device abbreviation.http://starwars.wikia.com/wiki/Power_droidhttp://starwars.wikia.com/wiki/GNK_power_droid

author: johnnyfp
author_rank: Frequent Contributor
timestamp: April 20, 2012, 09:36:52 am
content: $1200! For a nimh battery. Bit excessive really.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 20, 2012, 10:23:02 am
content: Quote from: johnnyfp on April 20, 2012, 09:36:52 amIt isn't for a nimh battery, it is for a low noise high resolution power supply with optically isolated controls and a pair of battery packs with a switching and charging circuit.The way this thing works is that there are two batteries. At any given time, one is charging and the other is powering the circuit. When one battery is drained, some relays flip and the live battery is switched in to power the circuit while the dead battery starts charging. The result is that you have a battery powered floating power supply that never runs out of juice. They also claim that they reduce the switching transients to nearly nothing, but I don't know how they do that.This is tied to the SRS 'SIM' rack, but that is good for its designed application. The purpose of this supply is to provide bias voltages for floating sensors or to power a small sensor preamp. In any case, the signal would then be sent to a non-floating amplifier built into the SIM rack.Sure, the parts cost is still only a small fraction of the sale price, but compared to paying someone to build an equivalent product the price is cheap, and I don't even know of any competitive product on the market.SRS makes great products, and they are really reasonably priced if you compare to people like agilent. They were really leaders in low noise digitally controlled electronics. Their instruments have good low noise analog design, and their digital components are very well isolated from the analog side. A technique they use in some of their preamps is actually to stop the clock on the microcontroller except when you press a button or send a serial command, to completely eliminate the possibility of digital noise creeping into your analog signal path.Their main drawback is that they rarely update their designs. A lot of their DSP instruments like their digital lock-in amplifier and spectrum analyzer are still using DSPs from the early 90s, and several of their instruments ship with floppy drives. This is good in terms of having a lot of confidence that the device you buy today will work as well as the device you bought 10 years ago, but definitely they also suffer limitations due to the products available at the time. A lot of their analog frontends use monolithic matched jfets that are easy to blow out and hard to replace.

author: EEVblog
author_rank: Unknown
timestamp: April 20, 2012, 12:29:31 pm
content: Quote from: ejeffrey on April 20, 2012, 10:23:02 amApart from the matched JFETS which I've encountered myself, SRS products generally are designed with really old school jelly bean parts. They just brute force it using lots of parts instead of going custom. And they provide very nice full schematics and service manuals.Dave.

author: Crumble
author_rank: Regular Contributor
timestamp: April 20, 2012, 01:36:23 pm
content: Quote from: johnnyfp on April 20, 2012, 09:36:52 amI must agree they are really expensive. It should be possible to build a high-quality similar unit for only a fraction of the cost. Even switching between two batteries can be done with a relay or so with a capacitor providing sufficient charge for the few milliseconds while switching.I might even start developing a similar unit myself. Hopefully I can obtain the type of connector like on those electric water boilers so you can place your power supply upon it when you don't use it and it will start charging automatically. Dave, your design might come in very handy indeed! Love it!

author: T4P
author_rank: Super Contributor
timestamp: April 20, 2012, 02:20:08 pm
content: Quote from: Crumble on April 20, 2012, 01:36:23 pmBut for the accuracies which complement some epic amount of design , planning and production , it certainly is cheap .Getting somebody to manufacture them will drive you crazy over the prices they easily quote .

author: Crumble
author_rank: Regular Contributor
timestamp: April 22, 2012, 08:59:58 pm
content: Quote from: Dave.S on April 20, 2012, 02:20:08 pmVery true. It is probably a rather ambitious plan.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: April 23, 2012, 05:34:12 am
content: SRS have a strong position in test equipment for anything to do with lasers, and it's for good reason. I found their products performed well and were very easy to use as well. The service is good as well - you can call and speak to an engineer very easily. The price of a product isn't just the parts.