Author Topic: power for a custombuilt hot tub  (Read 3503 times)

dannyreader

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power for a custombuilt hot tub
« on: December 04, 2014, 12:36:12 PM »
Hi,
I'm looking to use solar energy to power the pumps and other electrical items for a custom built hot tub project I am currently under way with.
I am looking to use a 12v water pump which will draw 4 amps, I hope to have this running continuously if possible. I will also run a 12v air-pump for the jets which draws 2amps, a 3kw water heater which I worked out to be around 13amps (will might be connected of a 3kw 12v  inverter). Then I will have some lighting running of the system but these are 12v led light strips which should only draw 5 amps max and maybe a converted car audio system(no sub). I estimate that I will use the tub for a couple of hours at a time tops, so with the total estimated amp usage of 30-35 amps per hour so when in use it will use about 70amps without the water pump.
for a battery bank I plan to use 6x 12v batteries with each having a capacity of 50ah or may go for 10 batteries at 33ah giving me around 300-330ah,
for solar panels I plan on getting 3x 100watts panels.
for controllers I haven't got an idea for which one to use, that will be suitable for the system.

I expect I will use the tub more in the summer but maybe twice a week on average,
I'm just uncertain if the method I've thought up to power the tub will be enough or if it is totally wrong as it my first solar project.
I say I have a good understanding of electronics and electrical installation as I'm a apprentice electrical engineer

SeanB

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Re: power for a custombuilt hot tub
« Reply #1 on: December 04, 2014, 12:56:00 PM »
The solar panels will not work at all, especially if you want to have heating, which would be better using either gas or a very large flat plate solar collector to do the water heating. A 3kW heater off an inverter will be drawing around 300A from the battery, more than the typical starter motor.

A 300W panel will deliver around 25A for charging for around 6 hours per day at best, slightly more with a MPPT controller, but you will then just barely be able to cover the pump running power. Running the pump during daytime for a limited time at around noon will at least give you the ability to have the battery charge without the pump load, and the pump will have to pass water through the plate solar collectors to heat the tank.. The air blower and lighting will not be able to operate full time, perhaps for a few hours a night till the battery is partly discharged. That might give a hour or two every night of use, or a little more on a weekend if you do not use it during the week so the battery is fully charged.

dannyreader

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Re: power for a custombuilt hot tub
« Reply #2 on: December 04, 2014, 03:22:45 PM »
Okay thanks I worked the heater out to run at 13 amps, and surely the solar panel would produce more than just 25amps over the 6 hours?

SeanB

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Re: power for a custombuilt hot tub
« Reply #3 on: December 04, 2014, 11:26:18 PM »
13A at 240V, while the panels will do 25A at 12V. 3000W versus 300W. 6 hours is about the time the panels will produce usable power, as they are not tracking, so will have less efficiency or no output outside of a window around noon when they should be facing the sun direct.