Split pv energy with toggle switch

[Salvador]

Hi everyone, I just finished converting a small campervan and want to add a couple of extra perks here and there. Recently I stumbled upon 12vdc heating elements, and think this is the perfect solution to heat up my shower water (20 liter deposit). However, the element drains a lot of my battery energy (its rated for 300W and can be configured for 150w). So now I’m thinking of just having it wired straight to my 150w solar panel and having a manual toggle switch to divert the pv energy between my solar controler and the heating element (with a fuse in between).

I’m looking into DPDT toggle switches, but I can hardly find 12vdc (found one with expensive shipping rates) with high amperage tolerance (say 25A). So I started to question if these are uncommon for 12v systems.

There are however, many SPDT switches for12v systems. But making this connection means I need to split my positive pv energy using a Ymc4 connector. And this is where I’m not sure what happens to the pv energy going into my battery bank if I split the positive solar cable in two just before the toggle switch.

Would be apreciate of any advice regarding the two options. I want something simple as turning a switch on or off to divert the solar power. Not looking into automatic relays or diverters or anything of the sort.

Thank you in advance

 

[TheDroidsYouAreLookingFor]

Relays are some of your best options. They have been used for decades in vehicles and can be found inexpensivly. If you want to do something custom sometimes you have to build something custom. bonus is that you would still have nothing more than a switch on the dash or wherever showing inside.

 

[efficientPV]

(its rated for 300W and can be configured for 150w)

I assume this is a dual element wired in parallel. 150 is only one element. Putting both elements in series can get you down to 75W. Figuring for 150W, 1000WH/ 6gallon/60F, that will take 6 hours of really great sun.

 

[Salvador]

I assume this is a dual element wired in parallel. 150 is only one element. Putting both elements in series can get you down to 75W. Figuring for 150W, 1000WH/ 6gallon/60F, that will take 6 hours of really great sun.

Yes, its the dual element 12vdc. Using the brass plates in parallel gives an output of 300w, removing one of the brass plates it becomes 150w.

Where I live we get about 80% of clear days from June to October and median temperatures of about 27c. So sun power is more than enough. However 6 hours is way too much. I’d like to think I’d be able to warm the water temp enough within 1:30-2 hours.

When I connect the element (configured to 150w) to the 12v battery, it takes about 1-1:30 hours to heat around 3 galons (12 liter) to around 32c (90f)

But I don’t know how to calculate how long it would take when connected straight to the 150w solar panel. My solar panel puts out a Vmpp of 17.42v and Impp of 8.61amps.

Should I look into a stronger element ?

 

[mikefitz]

B
ut I don’t know how to calculate how long it would take when connected straight to the 150w solar panel. My solar panel puts out a Vmpp of 17.42v and Impp of 8.61amps.

 

[mikefitz]

Although it's a 150 panel it won't match the load of the heater and conecting directly will be very inefficient.
I suggest using a MPPT solar controller and using the battery as an 'energy ' store. The 150 watt panel wont be putting 150 watts into the battery, with losses and reduction of power due to temperature rises, 120 to 140 watts at best.
Using the 150 watt element, 10C rise in temperature of 10 litre of water will take around 0.8 hr.
For a 40C shower and starting water temperature of 20C with a10ltr store you are within the 2 hours.
Over the 2 hours the battery has lost 300 watt hours for heating but with a solar gain of say 240 watts hours over that time, it will need a further 30 minutes to fully restore battery lost energy.(The maths are simplified, for the example in practice it may take longer due efficiency of charging).
In summary use a MPPT controller to extract maximum power from the panel and use the battery as a buffer store for the energy needed.
Use automotive 12v relays to switch power to the heating elements.

Mike