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Topic: Hot Tub (Read 4242 times) previous topic - next topic

Slausonm

OK,  I purchased a used hot tub a few years ago and spent about $150 dollars replacing the mechanical relays with new. Last year during a storm, I had the tub plugged in. We had a power surge that destroyed  some lights, but I thought everything else had escaped injury until I tried the tub. The contacts in one of the relays must be welded closed because the tub circulating pump won't turn off.

So here are my thoughts.  Replace the circuit board and relays with an Arduino controlled relay board. The tub currently has a float switch that turns the heater off when the circulating pump is not flowing water through it. This is a 110V switch but I could use the same rewired switch for logic to the board. Or is this a safety issue that should still turn off main voltage? It also has a circuit that turns the heater off when the air pump is on high. The temperature is controlled by the heating unit which has it's own thermostatic switch for turning off the heater when temperature is reached. It would be nice to add temperature feedback and control through the Arduino, but for now I would be happy to have the Arduino control Water Pump High and low speed,Air pump high and low as well as heater on/off.  If I remember correctly the  heater is 220, air pump 110, pump motor 110V.  Can someone recommend a suitable (inexpensive) relay board that I could use to try this? I know I am playing with water and electricity  It is all on a GFI circuit.

daveg360

Think you're going to need to provide so more details regarding the current requirements of the various bits.  SSRs seem to lend themselves well to your setup.  Be wary of removing any safety interlocks as the manufacturer probably didn't put them in just for fun.

P.S I suspect you could be stone dead before your GFI kicks in.  My electronics lab back in college was protected.  We were warned in no uncertain terms that it wouldn't stop us being killed though.  I suspect you'd just be a better looking corpse.

MarkT

Yes, GFI only protects against shorts to ground, no guarantee it would notice a fatal current to the human body (a few mA).  However live voltage shorting to ground will trip the GFI and prevent the ground being at a lethal voltage for long enough to cause damage.  So it protects against some faults - not every possible fault.  You do need to ensure that all grounds are protected (such as the low voltage circuitry you are anticipating) by bonding them all together - thus should live hit the Arduino it will flow through the GFI and trip it.   Consult a local qualified electrician too ;)

Water appliances usually have proper grounding, double-insulation in the various motors etc, and a GFI...  Since it was damaged by the storm you might want to get the grounding re-tested in case its been damaged.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

retrolefty

#3
Mar 07, 2011, 12:42 am Last Edit: Mar 07, 2011, 09:49 am by retrolefty Reason: 1
Quote
Yes, GFI only protects against shorts to ground, no guarantee it would notice a fatal current to the human body (a few mA).


I don't think your read on GFI protection is accurate. Standard circuit breakers are designed to protect against shorts to ground or current draw in excess of the circuit breaker's current rating only. GFI breakers or outlets, on the other hand, are designed to protect against shock hazard to people. A GFI can detect an imbalance of current flow between hot and neutral conductors with the assumption the the imbalance represents flow from hot to ground, perhaps through a person, and can trip on an imbalance of just a milliamp. They are indeed designed to prevent fatal shock hazards to people and that is why they are a code requirements for bathrooms, kitchens and even house exterior mounted outlets, depending on local building codes.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html


Slausonm

Since I don't intend to change how the exsisting wiring is grounded to the GFCI circuit I won't be affecting the safety of the original design.  All of the wiring for the main voltage will remain essentially un changed, it will just be triggered by digital relays rather than the relays that are in the unit now. My options are to buy replacement relays as I did before (which worked fine until the storm) or to add different relays and controls using the Arduino as a feedback system to control the original but very simple functions and possibly add some functionality like temperature monitoring and control later. Possibly even add a wireless remote control to the arduino to activate the tub remotely. 

I know current ratings would be helpful, but I don't have them right now. So any thoughts on the original question about relay boards...without this info?

Thanks, Matt

daveg360

Honestly you're going to need to supply more details.  Relays start at a few dollars for something that can handle an amp.  I suspect you need to be able to handle up to 60A which makes it a much more difficult task.  As I suggested previously - take a look at solid state relays.

Retrolefty - I know what you're saying.  However, seatbelts, airbags and crumple zones will probably allow you to walk away from a 20mph crash into the side of your house.  I still wouldn't advocate that you use the side wall of you house to stop you when you get home from work.

retrolefty

Quote
I still wouldn't advocate that you use the side wall of you house to stop you when you get home from work.


Just explaining the difference between a circuit breaker and a GFI module. Did I state something unsafe or recommend  not using one where required?


daveg360

I think most folks on here could think of a way of killing yourself without ever tripping the RCD (GFI).  A good pair of wellies(gumboots) and two arms would do the job nicely and not beyond the realms of possibility with a backyard hot tub.

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