We are trying to fix a problem with a float switch that controls an automatic fill valve in a small (15' X 15") decoraive fountain.

The float switch is installed in the fountain inside of a still tube to prevent unnecessary switching.

The float switch controls two time delay relays and switches about 20mA at 24VAC.

The switch is a reed switch and is designed to handle .5 Amps at 120 Volts.

The problem is the switch starts sticking after a few days or within a week. We don't believe that it is a mechanical problem.

Everyone we talk to agrees that the switch and the design should work but yet we are still having problems.

HELP!

Does anyone have experience with fountain or similar controls? Has anyone came across this problem before?

Thanks
Brian

[This message has been edited by master66 (edited 09-22-2006).]

[This message has been edited by master66 (edited 09-22-2006).]

Again, contact the mfg. and get their fix, they pay their tech support folks to have the answers, it builds repeat business, for both of you.

Are the relays this switch controls inductive, producing a "spike" back to the reed switch when it opens, casuing arcing? Maybe you need an interposing relay driven by the reed switch, which then feeds your timedelay relays. An interposing relay has a small coil burden, and a diode and resistor to squelch the spike.

Just a guess, perhaps you have already looked at this.

Mike

I have installed float switches for similar applications. The float switches were stainless steel and were from Dultmeier Sales. I think the model # was 2A551. Going on 2 years now with no problems.

I should have mentioned in the original post that the relays that the switch is controlling is two solid state time delay relays from idec.

We have been in contact with idec and the switch manufacturer and they can't figure it out either. Idec says that thier relays would not cause a spike.

We would like to find a murcury tilt switch that would fit this application but have been unable to find one. We are also considering a probe type switch system.

The switch mfgr said that they ran into a similar problem a few years ago but couldn't remember what they did to solve it. The guy that dealt with the problem was not in today but will be back in on Monday. He thinks that they might have installed a varister across the switch or possibly a capacitor. We will be talking to him on Monday.

leespark,

what was your switch controlling? Was it the same as I have described?

Brian

[This message has been edited by master66 (edited 09-22-2006).]

[This message has been edited by master66 (edited 09-22-2006).]

For the life of me, I can't figure out why you have one float controlling two TDRs. You usually see 2, NC, open on high water float switches in series driving a control relay. A NO sealing contact of the relay would be paralleled with the lower setting float switch. You really think of the lower setting switch as closing on low water, instead of opening on high water. There are various switches that allow deadband adjustments with a single float but those are usually touchier to adjust. Is there more to this that you're not sharing? Do you just want to open the fill valve at x" and close it at x" + y" ???

I work with some used oil day tanks that have reed switches in a SS shaft. SS floats with magnets travel berween collars. I have seen them ordered and installed with the wrong contacts. Fortunately I was able to switch the contacts by moving the collars up or down a little. I have never had the units stick. They all pick cube relays @ 120 VAC.

The only pump controls I work with that use TDRs require pre-libe of bearings on long pump shafts. The floats and alternator trigger a >= 1 min pre-lube and then start the pump(s).

Are you using these delays for alarms or to detect if you haven't filled the tank within the allowed time?
Joe

If you have a pivoting float arm that works, you could epoxy onto it a mercury bulb switch taken from a mechanical HVAC thermostat, many of which have three contacts for SPDT uses.

FWIW... Much to my amazement, there are different internals used in float switches! Reed switches, sliding contacts, mercury vials... you name it.

The hardest thing to design into a float switch is a 'dead' zone between 'on' and 'off.'

I have had much, much better luck, and better reliability, with the ones using mercury vials.
What is interesting is that the vials have a partition inside, with the effect of making the cylinder act like an hourglass. The float has to move significantly from horizontal for the mercury to flow into the other half. This leads to a 'definite' switching action, rather than a 'maybe.'

If your local plumbing supply doesn't have them, e-mail me for a reccomendation.

My situation was in the bottom of an underground vault which houses several pumps for decorative ponds as well as an electric panel, timeclocks etc.

A sump pump was installed at the bottom of the vault. That particular float was installed to allow the pump to run even when a small amount of water entered it. We used a simple "RIB" relay to operate the pump. I know the pump operated quite frequently and as I said no problems to date.

The float switch is connected to two TDR's as such.

TDR#1 must be energized by the float switch for a preset time (5 min. solid) before the fill valve is turned on. This was done to prevent the valve going on and off when the water level was at the borderline.

TDR#2 is a shut down timer. If the float switch is not satisfied within a preset time (about 1 hour) this timer shuts down the fountain completely. This was done to prevent over flow.

There is also an off delay timer that is controled by one of the on delay timers. This is connected so as to keep adding water for a preset time after the float switch is satisfied. (about 20 min)

The water level must be within about an inch and a half to two inch area for proper operation.

We redid all of the controls but redid them the same as the original design.

Brian

use a bindicator. they're non contact, can't plug, bind, or get you in the water. it's like a probe but doesn't require capacitance of the liquid for sensing.
http://www.bindicator.com/pdffiles/LAG180180.pdf

We will check into the Bindicator. But, we only have 2 feet of water and we don't really want to mount anything above the max water level where it would be seen.

How would we mount this in our application?

Brian

As i recall, the bindicator needs about 5" of pipe in the water to toggle the switch. You could hide the sensor head in some decorative piece setting in the fountain.

One of the other guys in our company asked about induced voltages on the float sensor wire.

The float sensor wire (#12 THHN) shares a conduit with some of the fountain lights. (2 circuits). In the pit where the controls are located, the sensor wires share a conduit with lighting circuits as well as pump circuits for about 12 feet of conduit.

There is an induced voltage on the sensor wires. About 20 Volts on each wire with the sensor disconnected. He thinks that the induced voltage being present in the sensor conductors along with the control voltage of 24 volts may be the cause of the sticking contacts. I'm not so sure. Welded contacts, I believe, are a result of excessive current not excessive voltage.

We may, however, test his theory by installing a sheilded cable for the sensor.

We cannot, without major alterations to the fountain, install a seprate conduit for the sensor.

What do you guys think?

Brian

Induced voltage may trip a solid state relay, but I'd doubt it would melt dry contacts...as you said, that's from too much current. Hwhy don't you just run the fountain with the lights off and try it, or is this unacceptable to the client?

Try contacting these guys with your problem, they sell controls as well, might have a solution or advice for you! http://www.fountainpeople.com/site_2/index_home.htm

Mike

The SSRs I am familiar with (Crydom and ISO22) exhibit about 1000 ohms of resistance. I don't think you will induce enough current to "trip" it with incidental proximity to other conductors.

UPDATE

On Friday 10/6, as per my fellow workers recomendation, I installed sheilded cable to the float sensor, Grounded the control transformer secondary(24VAC) and rewired the controls so that the float switch is switching the grounded conductor to the time delay relays. The fountain has been working fine since. 11 consecutive days is a record.

So, why did I have to do that. And, what fixed it. Grounding the transformer? The sheilded cable? Or, switching the grounded conductor? Tell me what & why???

Brian

*** UPDATE ***

The switch started sticking again the day after my last post. It is sticking on average every three days.

OK Master66, I haven't been thrilled with the control scheme as described. Please use a Fluke or equiv. with min/max record on AC amps , then AC mA. to make and break the circuit in place of the reed switch. Also check it on fast min/max record if you have that setting. Then also please tell us the actual measured value of your 24VAC control voltage. Also, if you can secure things, leave your Fluke on ACV min/max record across the 24VAC and walk away from it for a while. Check for higher voltage excursions. We can use the data gathered to determine if a current limiting resistor might be appropriate to protect the reed yet still provide enough to the coils.
Joe

Are you sure the contacts are actually sticking, i.e. do they stay stuck even when not powered? Reed switches are operated magnetically. Even though you are in a still tube, level fluctuations could be "chattering" the switch and causing the iron strip inside to magnetize semi-permanently. The fact that they felt it necessary to debounce the circuit with a 5 minute timer makes me think that this was a problem they were trying to solve. The problem with that solution is that it only solves the control issue, the reed switches themselves may still be operating too frequently. Here is a web site that describes how reed switches work. I have found that as reliable as they are, they cannot be used for high speed high switching count operations because of that magnetic memory issue. http://www.osdc.co.jp/english/products/products.html

Or is it just that the timers are not de-energizing when they should? I have definitely had 24V circuits get enough energy induced on them to keep solid state circuits energized, even if it wasn't enough to energize them in the first place, essentially a seal-in of the circuit. A small resistor across the terminals of the time coil should take care of that.

The simple test would be to see if everything goes back to normal as soon as you take power off the circuit. If it is an induced voltage issue that is keeping the Idec TDRs from dropping out, they should drop out again as soon as power is removed. If the reed switches are sticking closed, they would stay that way until the residual magnetism dissipates.