Diverter on JD H260 - switch problems

[KY Gun Geek]

Working through installing a diverter to work a grapple lid on a JD 5093e with an H260 loader. I have 2 issues that I don't think are related - slow bucket curl, and switch destruction. I have posted 2 threads to keep from confusing things.

Here's a link to the bucket curl thread:
http://www.tractorbynet.com/forums/hydraulics/375267-diverter-jd-h260-slow-curl.html#post4687660


I am on my 3rd switch and it has failed, too. They seem to fail after 20 - 25 presses. Valve is spec'd to draw 3A, I have measured it at about 2.6. There is a 5A fuse in line that has never blown. First and 2nd switches were rated at 3A, then 5A. Current one is at 8A. They are screw terminal, so no soldering (i.e. heating the contacts). Failure modes have been the same - switch becomes unreliable, then stops working all together. The valve has an LED that lights when voltage is applied with correct polarity - new switch starts working great, light is clear and bright, then doesn't come on everytime button pushed and LED flickers, then stops working. If I remove the switch and short the wire, valve works great. Coil does not feel hot - not holding switch down for extended period.

Here's my last switch:
Dorman Products - 84822

Any ideas? Are we dealing with "flyback" - a reverse voltage spike generated with the coil field collapses - see below. This valve is pretty common (bought from Surplus, link below) - see lots of folks here using it, anyone else have a problem? I haven't seen a mention of the LED here. Is this a new mod that might be causing a problem? Seems like the mod shouldn't make the spike worse, the LED would just be in reverse polarity and not do anything.

Called Surplus and they said if I sent valve back they would test it on the bench. They also said that given that I see a 2.6A draw, they probably would as well and call it good.

I guess I could test theory by taking switch out and shorting the wires. If there is a spark when I move the wires apart, then flyback is prolly the issue.

If you are interested, a little googling turns up this:
"Since an inductor (the relay coil) cannot change it's current instantly, the flyback diode provides a path for the current when the coil is switched off. Otherwise, a voltage spike will occur causing arcing on switch contacts or possibly destroying switching transistors.Feb 18, 2014"

If you just really have to study up:
Flyback diode - Wikipedia


Spec info just in case...
TractorData.com John Deere 593E tractor information

12/24 VOLT DC 13.2 GPM SAE 8 SOLENOID OPERATED DOUBLE SELECTOR VALVE

 

[BukitCase]

Don't need to follow your links, you're on the right track. Having spent the last 35 years of my working life doing industrial instrumentation/control, I've seen less than 1 amp inductive loads (mostly solenoid valves, just smaller ones than the diverters) take out 10 amp rated switch contacts in a few days til a clamping diode was added. Most of the time I got away with 1000 PRV rated 2.5 amp diodes; in this case, you'd probably want a diode rated at least the amperage of the coil, might wanna look for a 1000 volt @ 5 amps.

If you can't find one that high a rating that's still axial leads, it'd be worth trying a 2.5 amp rated but be sure you stay at LEAST 1000 volt rating (NOT a typo - but by now, you already KNOW that :=)...Steve

 

[KY Gun Geek]

I may be mired in group-think, but I haven't seen any mention of this being issue on this board, and there's lots of these valves discussed. Surplus didn't seem to know anything about it.

I'm also a little suspicious of the LED (and resistor) pinned across the terminals. Surplus doesn't show it in this instruction sheet (below). In fact, it could be pretty easy to get the polarity backwards and the LED wouldn't work - there's no note of it at all. Seems like a "quickie". I suppose for a short time the LED would prevent the flyback, but would prolly burn up quick.

Time to diode shop. I have have diodes used for just this purpose in electric golf carts (cuz I have golf carts). Those things are current and torque monsters, and they have a relay that will light you up if you don't have a diode on it.

http://www.surpluscenter.com/_MoreSpecs/i9-8602.pdf

 

[KY Gun Geek]

Well, I couldn't find it via search, but quite by accident, I found this. Looks like it has been discussed. In this case it was only a suggestion. Will read more and see how it turned out.

Seems like surplus should be aware and or make a note on the data sheet.

http://www.tractorbynet.com/forums/...pple-hydraulic-setup-1026r-2.html#post2874456

 

[BukitCase]

Pretty sure I've mentioned the need for the diode in a thread or two, but don't remember which ones - but you're right - I doubt the LED/resistor is for anything more than an indicator of which button's pushed (or not) - and I bet golf cart relays really WOULD light you up with no diode, since they're usually at least 24 volts DC to start with - that should give one heck of an inductive kick - If you think about it, a car ignition's just based on turning OFF a coil, and even the older style with the right coils can put out over 50,000 volts (of course, I'm ignoring the fact that they're doing a lot of it because of the coil being an autotransformer)... Steve

 

[tre873]

You could always use the switch to control a relay. The coil side of the relay would pull way less than 1 amp through the switch. Most modern relays have a diode across the coil to prevent the voltage spike from damaging the switch.

 

[BukitCase]

You could do that, but you'd STILL need a diode clamp on the relay's CONTACTS or you'd just MOVE the problem to relay contacts instead of switch contacts - still, that might be preferable if the switch is more expensive or harder to get at than a plug-in relay... Steve

 

[tre873]

You could do that, but you'd STILL need a diode clamp on the relay's CONTACTS or you'd just MOVE the problem to relay contacts instead of switch contacts - still, that might be preferable if the switch is more expensive or harder to get at than a plug-in relay... Steve

I would have to disagree. Relays are designed to handle large current loads without causing pitting on the contacts. You can get 12 volt relays that can handle 20 amps without causing pitting on the contacts. You can go even higher if you spend a little more. You should be able to get a relay and connector at most parts stores for less than $20.

 

[BukitCase]

It's not the main current that's the problem with ANY mechanical contacts when switching an inductive load - it's the KILOVOLT or more of back emf that ARCS across the contacts every time they OPEN. For an extreme example, google "arc flash" ... Steve

 

[tre873]

I'm well aware of the voltage spike that occurs when a magnetic field collapses. The relay contacts aren't near as susceptible to detoriation as the switch contacts are. If the OP uses an automotive grade relay, he won't have anymore problems. Think about the number of cycles a typical automotive relay endures during the lifetime of the vehicle. Automotive relays have a suppression diode across the coil side only. You won't need a suppression diode on the load side. Think about how long a set of points would last on a gas engine. Points opened and closed 100's of times a minute and would still last 5-10 years under normal use.