Hot tub circuit board

[GbreadMan]

Hey all,

Repairing a hot tub PCB (Balboa 25501 off a Coleman hot tub), thought I'd share the progress. These boards fail frequently, especially the relays along the 240v heater circuit (I've gone through two already), and are $600 ($200 at the cheapest on eBay). It's my first major circuit board soldering project in a couple years, I built some home-made solar panels last year so got some practice with a new iron.

Most of the problem was centered on a relay failure, but the relay smoked before the fuse could blow, causing two large KME caps to get a tad too crispy. I replaced both with UCC caps, KY 25v 2200uf and an LXY 50v 1000uf. ESR says the old ones are OK but why chance it, this board is about a decade old. And caps with char marks on them is never a good omen.

I'm using a Weller WES51 analog 50 watt which has just barely enough heat to melt the negative side of the caps on the ground plane. I cut my teeth on a varistor that had taken a big hit, and then proceeded to the caps.

The caps were fairly easy to replace. I cleaned the holes using a large metal paper clip while melting the solder from the other side. Getting the relay out was a PITA but eventually got it out. Finding replacement American Zettler 18 volt DC relays for a decent price +S/H was impossible (AZ8-1CH-18DE); ended up purchasing 24 volts instead. Most hot tub retail sites want $30 per 18 volt relay, plus shipping (Zettler no longer produces 18v relays).

Didn't see many hot tub circuit board threads on here, so I thought I'd share. Will keep everyone updated if/when it's installed. Pics are 1) Board with new caps/red varistor, 2) old parts plus new relay, and 3) another pic of board (relay will be installed in the foreground of the varistor).

Dan

[japlytic]

Re: Hot tub circuit board

12V relays (of the size in the pictures) can be converted into 18V relays with a 6.2V 1W zener diode in series with the coil (cathode to 18V rail, anode to relay coil opposite switching transistor).

[GbreadMan]

Re: Hot tub circuit board

Thanks for the tip, that will help a lot. I am learning as I go. I bought a 4-pack of the zettler 24v relays because I am working on other 24v projects where they might be useful. They cost about $9 each after shipping from Radwell Int'l. They were shipped very quickly (arrived 24 hrs later) and it was generally a good experience, albeit a higher price than I expected. I guess I'll get a couple 12v, too.

It's a shame digikey or Mouser doesn't have these smaller Zettler relays. I can get the larger T90 relays (ones with yellow coils in the pic) for $3 each from digikey. Most online Zettler distributors either want $20+ each after S/H for the smaller relays, or 1000 units for $3 each. Some places like onlinecomponents.com don't even give you the S/H charge until after you give them the credit card and place the order; they can charge whatever they want (onlinecomponents is rated one star on some review sites).

Anyway, the replacement caps are pretty tall and the lead space is a tad narrow, but luckily everything aligns and the location in the hot tub is pretty spacious (albeit in close proximity to lots of highly chlorinated/brominated water).

Thanks,
Dan

[kaboom]

Re: Hot tub circuit board

A high-resistance connection (bad contact or solder) on the relay will not blow a fuse!

It will make an awful lot of heat, while causing the current to go down.

And if the fuse is for the control power, it's nowhere near or relevant to the heater circuit.

The ckt bkr takes care of heater and motor OCP and shorts. And, hopefully, it's on a GFCI. The motors probably have their own running-overload protection OLs inside.

[bluto]

Re: Hot tub circuit board

Good luck on the repair. I guess since we are talking hot tubs now, I can share my only tidbit of repair knowledge there. On my tub, the LED light developed issues when the tub was still very new. This doo-dad takes the place of a regular 12v light bulb on the side of the tub. It has 9 LEDs (3x red, green, blue) and makes various color patterns by way of small on-board micro. Anyways, the issue was that the blue channel stopped working suddenly. I finally figured out that the LEDs for each channel were wired in series. And one of the blue LEDs failed causing the other two to go dark. Replacing the one bad LED brought it back to life. Looking back, it is weird because it has to have been the first time I have ever seen an LED go bad. Especially since it was young and being 'used as directed'.

[Longbow]

Re: Hot tub circuit board

Interesting problem. You say that many of these boards fail and it would be helpful to you to get a handle on exactly what is failing and in what order. Obviously if the caps are filters on the 18 volt line, your relays will not have the proper pull-in voltage. The relays may spark due to lack of contact force and if so, the contacts wear out quickly. Sparking translates into hot relay contacts and melted solder pads on the board.

Changing relay coil voltage is not a simple swap. Whatever the coil voltage, the relay contacts must be rated for sufficient current and voltage interrupt (opening and closing of the contacts). An equivalent 12 volt relay will certainly require more coil current to achieve the same results. I would look into the possibility of increasing the coil control voltage up to 24, which is more common, and better suited to high current applications.

Remember to use a thin film of dialectric grease or contact spray on the high current connections to the board. Let us know what you find.