Hot Tub Current Sensing Question?

Tue Feb 7 13:10:57 EST 2017

James,

I’m writing because I just heard from another vender with another current sensing product that you may think is better for my application on the hot tub. Here is their information:

http://www.crmagnetics.com/relays/cr7310 <http://www.crmagnetics.com/relays/cr7310>

and here is their data sheet:

Now there is a big difference in price of $23 vs. $136, the further the cheaper one is self powered while the expensive one will need a 24v power supply, but I only want to do this once… and correctly so I can have this added protection, so depending on what you think, in this case, price is not the object.  The assurance that I have another system in place that is consistent to warm me of hot tub problems is the objective.

Thanks,

George

> On Feb 4, 2017, at 4:00 PM, george handley <ghandley at kc.rr.com> wrote:
> 
> Dear James, and any other hot tun List owners,
> 
> Back in December you responded to my above question regarding the current sensor I found here:
> 
> http://www.digikey.com/product-detail/en/cr-magnetics-inc/CR9321-NPN/582-1021-ND/1045177 <http://www.digikey.com/product-detail/en/cr-magnetics-inc/CR9321-NPN/582-1021-ND/1045177>
> 
> Here is the URL to their data sheet on this product:
> 
> http://www.crmagnetics.com/Assets/ProductPDFs/CR9300%20Series.pdf <http://www.crmagnetics.com/Assets/ProductPDFs/CR9300%20Series.pdf>
> 
> and you asked some good questions which it appears I failed to ever answer due to other pressing matters. I hope I have now provided below the readings you requested.
> 
> You asked: 
> 
> "You should measure the idle current into the thing and make sure to get the proper sensor so that current will be off. That current might be nothing at all, but I’m not sure how you’re measuring or where exactly you’re planning to put the thing.”
> 
> First off, I measured the idle and running current at the GFI in my basement breaker box, but intend to install this current switch in the bowels of the hot tub itself.
> 
> The idle current reading without anything running was .05-.075 amps which I think is equal to 50-75 mA. The running amperage with everything running is 48A.
> 
> RE: "When the heater isn’t running does the circ pump still cycle though? “
> 
> Better still, the hot tub’s logic board is programmed by default to perform a daily “Clean-Up Blow-Out Cycle, in a controlled sequence, that will run all three pumps and air blower motor for two minutes everyday, 365 days a year.
> 
> My logic is to daily test the digital input reading* from the output of this relay. If the reading is anything but 0, then I believe I can be assured the hot tub itself is in working order for the previous 24 hours. Correct?
> 
> * I think this will be ideal with the new Weeder Relay board that not only has 8 opto-isolated output relays, but also two digital input channels. Correct?
> 
> Now here’s my question. From the .PDF spec sheet, am I interpreting correctly that this relay will not come on with anything less than 0.8 A? They use the term 0.8 AAC RMS max continuous,” and I’m not sure that is the same thing. I’m hoping it equally means 80 mA. Elsewhere it also states that the “Minimum holding current is 10 mA which concerns me.
> 
> Also, am I correct that each time the hot tub pulls more than 0.8A, XTension should see a “1” added to it’s register value? Again, my daily check of all critical sensors would expect that the unit designated for this relay to have a value of at least  “1” everyday. If it’s a 0, then I would know that something is wrong. 
> 
> With this information, have I found the correct current switch to do this job?
> 
> Thanks,
> 
> George
> 
> 
> 
>> On Dec 3, 2016, at 8:26 PM, James Sentman <james at sentman.com <mailto:james at sentman.com>> wrote:
>> 
>> 
>> Hello George,
>> 
>> Those are very good looking sensors. giving you just a transistor output for switching a digital input on and off above or below the setpoint. Easier than trying to measure an analog value that would tell you how much power it was using and having you try to figure it out. The only obvious problem I can see would be if the control circuitry of the tub uses enough current to turn on the sensor even in it’s not actually running the pump mode. You should measure the idle current into the thing and make sure to get the proper sensor so that current will be off. That current might be nothing at all, but I’m not sure how you’re measuring or where exactly you’re planning to put the thing.
>> 
>> When the heater isn’t running does the circ pump still cycle though? 
>> 
>> I am currently sitting at the third airport out of 4 that I’ll be travelling through today, my wife and I are escaping far far away to celebrate our 20th wedding anniversary. I will be online and since I”m not as into sitting on the beach as she is I will be checking email and responding, but things will be slower for the next week. Life returns to normal after next weekend when we have to spend another 13 hours on airplanes getting back home.
>> 
>>> On Dec 3, 2016, at 6:44 PM, George Handley <ghandley at kc.rr.com <mailto:ghandley at kc.rr.com>> wrote:
>>> 
>>> He has suggested this one below which is not exactly what I had in mind, but maybe will work:
>>> 
>>>> http://www.digikey.com/product-detail/en/cr-magnetics-inc/CR9321-NPN/582-1021-ND/1045177 <http://www.digikey.com/product-detail/en/cr-magnetics-inc/CR9321-NPN/582-1021-ND/1045177>
>>> My problem was that a hot tub sensor on the hot tub failed by itself killing the whole machine, and by the time I discovered it, the water was 52˚. 
>>> 
>>> My solution is to put 1 or 2 of these current donuts on the main line coming into the hot tub. Because the hot tub has a circulation pump that operates several times a day, I could test each morning the time delta of this (These) donut (s), and if it was less than 24 hours, I would then know that the circulation pump has been running, and that the hot tub is safe.
>>> 
>>> Does this scheme, with this sensor make sense to resolve this previously unknown problem and omission?
>>> 
>> 
>> Thanks,
>>  James
>> 
>> 
>> James Sentman                       http://www.PlanetaryGear.org <http://www.planetarygear.org/>		http://MacHomeAutomation.com <http://machomeautomation.com/>
>> 
>> 
>> 
> 
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