Paul, got some links for those?

On Nov 13, 2013, at 1:29 PM, Paul Miller wrote:

Colyn and others: why aren't we using a simple off-the-shelf motor controllers like those used in power chairs, golf carts, forklifts and other safety-minded devices?   They handle hundreds of amps, reversible, employ logic to prevent accidental reversal, work with voltages 12-48, programmable, log diagnostics and come already packaged in a heatsink and there are no contactors to worry about.  I see them selling for a few hundred dollars.   What bugs me about Adam's incident is that he had a switch in the down position and the pump ran in the UP direction.   We certainly have cheap access to the technology to prevent that from happening to someone else.   The scooter and forklift people can't afford to have someone go backwards when they press forward on the lever and this appears to be a mature area of motor control these days but we don't employ it.  Such a device would dump all the relays as I understand it.  On the Curtis models I reviewed,  external contactors like the one that failed on Adam's plane are still optional but the controller current is reduced to Zero before the Contactor engages or disengages.   I'm not seeing any downside and since the Oildyne pump is not a high amperage device (compared to a forklift) I believe a solid state controller can be directly connected to the Parker pump without the relays (solenoids).

What am I missing?

Paul

Legacy

On 13 November 2013 09:43, Colyn Case <colyncase@earthlink.net> wrote:

A lot of contactors are not really up to it.  Some things to look at in the specs:
- for Adam's application, life expectancy vs. break current.   See "resistive load performance" on the attached ev100 data-sheet or "estimated make/break power switching ratings" on the attached ev200 data-sheet.
- max break current.   If you have a short somewhere you will have large current.  Odyssey batteries can develop over 1000 amps for example.  You would like to be able to interrupt that current by de-energizing the contactor (e.g. turning off a master switch or pump switch)   Max break would be about the current associated with 5 cycles in the above charts.   You may have anl's everywhere designed to handle a dead short from anything to anything within one  bus.   However, there's no anl appropriate for a starter so you are really counting on the contactor to open that circuit if you need to.  Same issue with Adam trying to get his pump to stop.

Other things that might be of interest:
- hold current.  how much it takes to keep the contacts closed once they are closed.   Nice if this is low if you have an alternator failure and are trying to stretch battery life.
- physical integrity.  I think standard issue contactors are made from low grade plastic and stamped sheet metal.   It was when mine fell apart because of abuse during installation that I got interested in higher quality parts.
- I think there is a discussion on the archive about use of transorb's to minimize damage of the controlling switches due to field collapse in the contactor coil.

I think if you can even find the related specs on standard issue contactors, you'll find them less than satisfying.  (Marv - below attachments should be ~500KB together)



On Nov 13, 2013, at 9:04 AM, Adam Molny wrote:

Paul -
The gear relays are activated by applying a small current to the relay coil
terminals. That pulls the main contacts closed against a strong spring. When
you remove power the spring pulls the main contacts apart. There is a known
failure mode where the main contacts weld themselves together. When that
happens the relay will remain in the "on" state regardless of what the
pressure switches are doing.

-Adam
-----Original Message-----
From: Paul Miller [mailto:pjdmiller@gmail.com]

Adam, I don't understand how this happens unless the pressure switches on
the pump aren't shutting down.

Paul


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