Search 
sitemap button
Search using google with ads

 Tweet button  
Convert AC water heater to DC using low voltage
Resource: Convert heater to high voltage DC
Use only 600 volt wire.
Lamp cord, extension cords are not rated 600 volt.
Use copper wire only. Aluminum wire is fire risk and should be avoided or installed by professional.

30 amp breaker use 10 gauge /
120-240 volt 30 amp outlet can be installed on 30 amp breaker only/ use 10 gauge wire ... cannot be connected to 15-20-40 amp breaker.

Orange/ #10 gauge wire, with ground ... 30 amp capacity. Safe maximum: 30 x 80% = 24 amps.
Buy:
10-2 gauge/ 30 amp
10-3/ 30 amp
Southwire electric tools
Yellow 12 gauge 20 amp
120 volt 20 amp outlet can be installed on 20 amp breaker, but not 15 amp breaker/ use 12 ga wire.
... cannot be connected to 30-40 amp breaker. 1

Yellow/ #12 gauge wire, with ground ... 20 amp capacity. Safe maximum 16 amps.
Buy:
12-2 gauge/ 20 amp
12-3/ 20 amp

NMB is house wiring
UF is underground
Rolls of stranded wire
HOOK UP Wires
50-60 amp breaker use 6 gauge /
240 volt 50 outlet can be installed on 50 amp breaker only
6-2 wire
Buy:
6-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
40-50 amp breaker use 8 gauge /
240 volt 40 amp outlet can be installed on 40 or 50 amp breaker only
6-2 wire
Buy:
8-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
multimeter
Multimeters
Voltage is tested across two separate wires. Ohms or resistance is tested across both ends of same wire. Amperage is tested along one or two points on same wire.
Buy:
Analog multimeter
Multimeters at Amazon
Klein multimeter
Electric testers at Amazon
Clampmeter for testing amp flow on line
Southwire armored cable cutter
Electrical tools must be insulated.
Always best to disconnect power, but insulation failure, lack of proper grounding, grounded neutral, lack of GFCI, out-of-code wiring, generator operating without transfer switch, and other problems still pose a risk to anyone working on electric power ... even when breaker is off.

Buy:
Electrician tools kits
KLEIN TOOLS
Tools kits
IRWIN tools
KNIPEX

Telephone cable knife
Low Voltage Mounting Bracket for Telephone

Protect wiring from damage
Use nipper instead of pliers or screwdriver for removing staples (and nails). Do not damage cable or wires inside cable.

-Code says: Cable SHALL BE secured without damage to the outer covering. NEC sec. 336-15
Buy
End cutting nippers at Amazon


Electrically insulated tools
When removing insulation from wire, do NOT score or put cuts on surface of copper wire. Doing so increases resistance and heat on wire and creates possible weak point.
Buy tools:
KLEIN TOOLS
Wire strippers at Amazon
Electric Wire Stripping Machine
Linesman pliers
Utility knife at Amazon

GFCI circuit breaker
A GFCI circuit breaker will protect all boxes on circuit.

Circuit must be grounded. Ground wire must be continuous and connected to each piece of equipment.

White wire on circuit breaker must be connected to Neutral busbar inside the breaker panel.

Buy
GFCI circuit breakers
Push down
single-pole breaker          double-pole breaker
1" and 2" wide Push down breaker

Buy single-pole:
Choose from 15 to 60 amp
Eaton CL series
Siemens 15-60 amp
Tandem breakers
Buy double-pole:
Choose from 15 to 125 amp
Choose from 15 amp to 200 amp
Eaton CL series circuit breaker
Siemens circuit breaker
Double pole GFCI
Photovoltaic water heater Question from Jerry:
I want to heat water with a solar panel kit from Amazon that shows 400 watt and 12 volt DC.
Will it work if I connect it to the hot water element?

Buy:
12 volt 400 watt kit
Answer: Yes

... but how much hot water will you get with 400 watts and 12 volts? Let's calculate !!
1) Calculate using Basic formula for number of gallons of water heated Per Hour (for Electric heater) = (KW x 3413) divided by (temperature rise x 8.25 lbs per gallon of water)

2) If incoming water temperature is 65°F and you want to heat tank to 105° (typical shower temperature), or 40° rise in temperature.
400 watt or .4Kw x 3413 = 1365
40 degree temperature rise x 8.25 per lb of water = 330
So 1365 divided by 330 = 4.13 gallons per hour
If you get 6 hours of good sun = 24 gallons of 105° water 

3) If incoming water temperature is 50 degrees, and thermostat set to 110°  = 60 degree rise in temperature
400 watt or .4Kw x 3413 = 1365
60 degree temperature rise x 8.25 = 495
So 1365 divided by 495 = 2.75 gallons per hour.
If you get 6 hours of good solar = 16.5 gallons off 110° hot (indicating that a 12-20 gallon water heater is about correct)

Conclusion:
Calculations indicate that the solar panels will heat water for a shower and misc use.
Typical shower consumes 9 gallons 100°F hot, so a good day's solar harvest would probably give a couple quick showers if taken early in evening before tank cooled. For cooking etc you would have plenty of hot water.
Water is cooling as soon as it gets heated, so add insulation to the tank, and locate tank near the hot water usage points, then don't use any hot when you just need cold or new cold water is added inside tank, having a cooling affect on whole tank.
What is needed:
A 12-20 gallon water heater tank is probably best given the amount of hot water produced each day.
If the tank is too large, say 30-40 gallon, then it will be full of unheated water that will quickly cool the water that is heated.
Buy:
12 volt 400 watt kit
Rheem point of use
Dernord 12 volt element
Reliance water heater
Reliance 120 volt/ 1600 watt
6-10 gallon
Side connections/
6 year warranty
Buy:
Reliance water heaters
12 ga extension cords
12-2 Southwire cable
Resources
Reliance manual
State manual
American tiny titan water heater
American 120V/ 1500 watt
6-12 gal
Top connections/
6 year warranty
Buy:
American 12 gallon
12-2 Southwire cable
Resource:
American manual
State point of use water heater
Rheem
2-6-10-20 gallon
Side connections/
6 year warranty
Buy:
Rheem point of use
12-2 Southwire cable
Resource:
Rheem manual
single U elementWhat is needed:
You would have to convert elements on tank to same volts (12 volts in this example), and then match the wattage as close as possible.
This means you need tank with screw-in elements as shown above. Tank with bolt in elements or proprietary elements as found with Bosch will not work. Buy short element to fit tank diameter. Single U is probably easiest to work with.
If voltage from solar panels exceeds volt rating on element, then element will likely burn out.

Buy:

Dernord 12 volt element
DC elements
Single U 24 volt 600 watt element
Double U element
Question from Greg

I have 3 PV solar panels, and distance between Water Heater and Panels is 200 feet.

Setup
I have two 50 gallon water heaters in series. Incoming cold water goes into first heater. Then the hot water pipe from first heater feeds second heater ... and second heater feeds my house.

The first water heater was installed so I could take advantage of my 3 solar panels left over from my solar system on the roof.

Currently the first water heater is turned off.  Its wired for AC but not heating.  I'm letting the 2nd water heater do all of the heating for now.

What I want to do is use the 3 Panels to heat as much as possible in the first water heater, and let the second water heater finish the heating of the water.

Not sure the best way to utilize the panels.

My thought was to replace the bottom element on the first water heater with a DC element and let it go but not sure that's best and exactly how to do that and still meet safety, etc.
Alterations void product warranty
Response to Greg's question
It is unknown what your output will be for the solar panels. Is it low voltage or higher voltage? It depends on output of each panel ... plus if panels are wired in series or parallel.
So measurement is needed, and some planning.
Connect your panels at night so you don't get shocked ... solar panels don't have on-off switch.
I am going to refer you to my solar-safety webpage for more detail on safety.
Resources
Solar safety
Safe electric wiring

Wire the panels and Test volts
Wire your panels in series one night, then wire them in parallel next night ... check voltage output for each configuration.

Series means each panel end to end with positive from one panel to negative of next panel.
Just like batteries wired in series, amperage is equal to amp rating of any 1 of the 3 panels, and volts is three times the value of any single panel.

Parallel means all positives connected together and all negatives connected together.
Just like batteries wired in parallel, volts will be equal to the volt rating of any 1 of the 3 panels, and amperage is three times the value of any single panel.

After connecting panels, you test for voltage across two different wires, the positive and the negative wires that will travel to the water heater.
This test will tell you where to start with element voltage.
Remember, the voltage rating of element must be equal to or greater than voltage from solar panels. Why? So the element does not burn out.
If element is rated 120 volt, and you are feeding 100 volt DC solar into it, then that's good because element is rated for more volts than the solar.
You need ordinary multimeter for the voltage test.
Buy:
Analog multimeter
Multimeters at Amazon
Klein multimeter
Electric testers at Amazon

Maybe use series configuration with higher voltage since the distance is 200 feet. Longer distances cause voltage drop, so a larger wire is needed to help prevent power loss due to distance.
Except 3 panels in series @ 31 volts each would be about 93 volt at maximum solar harvest. In that case, the installation would not be 'low' voltage, and would likely burn out (melt) the thermostat pretty quick.
Another option: You could put two panels in series, and then into parallel with the 3rd panel.
Buy:
1500 watt 120 volt element

Test amps
Electricity has two dynamics: Volt and amps .... and standard formula is volts x amps = watts (power)
Measuring amperage is different than measuring voltage. Amperage is the flow of electrons along one wire.
Amperage only flows when the circuit is completed to the element. If the wire is just sitting there and not connected to element, then there is voltage potential across the two wires coming from solar panels, but no amperage is flowing.
You need a clampmeter to test amperage.
Buy
Clampmeter for testing amp flow on line

Size of wire
Here's the problem. The amperage must be known before selecting correct wire size for the 200' distance ... Why? Each wire is rated by the amount of amperage it can carry.
... but amperage can only be checked on your solar panels installation when power is flowing through the water heater element.
This means you need to install the wire before you know what size wire ... or make a best guess ...

I am going to recommend a #10 wire for 200' distance and 3 solar panels (6 solar panels and 200' might use #8 wire).
It's true, the smaller #12 wire might do fine for 3 solar panels and 200', but #10 will cause less power loss over long distance.
Note that having a wire that is a bit oversized is not an issue, and tends to run cooler with less heat loss, thus allowing longer distance without voltage drop and power loss.

Type of wire
Use UF-B for direct burial underground without conduit. I recommend using conduit for best long term result (ordinary NM-B wire can be used inside 3/4" conduit and is easier to strip than UF-B underfoot cable).
Ground wire is required for ALL installations. Do not make splices underground. Use 1 continuous piece of wire. Use solid copper wire. Code requires use of standard 600 volt wire. It is against code to use extension cord for any type of permanent electric wiring.
Buy:
10-2 gauge/ 30 amp
10-3/ 30 amp
Southwire electric tools

How to connect to heater
Typically this kind of solar connection would be made at lower thermostat and element.
Open lower compartment on water heater. Disconnect the two wires from top of heater ... cap them off and push completely out of the way.
Connect the two wires coming from solar panels to the thermostat and element.
You can keep upper part of tank connected to 240 volt AC without a problem.
Thermostat and element nust be covered with insulation.
Buy:
1500 watt 120 volt element

Will the thermostat work with DC power?
It will work fine for low voltage installation because it doesn't have a lot of force (voltage) pushing the electrons (amperage).
If your amperage flowing from solar panels is getting pushed by a lot of volts, it will burn out the thermostat pretty quick.
Why? Because DC has a problem with 'arc extinction' that AC does not have.
DC current causes more spark (arc and heat) when it's switched off ... making DC problematic for AC-rated thermostats (and other AC rated electrical equipment). Resource: Arc extinction

Thermostats are mechanical bi-metal switches ... nothing complicated about them ... and they work with any voltage (up to 480 VAC) ... and they replace easy.

Note: This design works but I cannot guarantee how much hot water it heats. Why?
Nobody has sent data on this project.
I have not done this project myself ... and there are no product manuals ... so I do not have real world information that tracks specific outcomes for series vs parallel, cold vs hot weather, high ambient temperatures vs cold, cloudy vs sunny regions, higher voltage vs lower, etc.
So the whole thing becomes an experiment requiring inventions and innovations by the installer.
HOWEVER ... I know this is a common installation for low voltage because people have emailed about having such an installation. So I know it works, but I do NOT know how much hot will be supplied on a daily basis or if there is a payback.
Install ECO protection?
thermostat terminal protectorReplace lower thermostat with upper thermostat... The ECO, or thermal reset button will cut power from solar panels if tank exceeds 170°F.
Yes this is good idea. Why?
The 240 volt on upper part of tank is controlled by upper thermostat with ECO, and it will cut power to 240 volt if top of tank reaches 170°, but will not cut power from solar panels, so panels are still adding heat to tank.
The tank has a TP valve that releases hot water if temperatures within top 6" of tank exceed 210°. The TP valve is designed to prevent steam explosion ....
You don't want water to get 170-210°F, especially if tank is older and might be weakened from rust etc. These temperatures can kill folks, causing severe burns plus destroy home, belonging etc.
Will your solar heated water cause tank to reach 170-210°? Without data from experimentation, I cannot say. But best judgment is that 3 solar panels cannot give that much heat (or even close) but it might be possible if more panels were added to the array.
Buy:
Therm-o-disc terminal protector
Camco 90-150 F thermostats
By-pass lower thermostat on 2-element tank?
This is one of the experiments I would try
Do not recommend by-passing thermostat with 1-element tank
Do not recommend by-passing thermostat with more than 3 solar panels

Since thermostats burn out with DC power, and that adds expense nobody needs, then a by-pass might be tried ... and it might work well.
Larger image
Use a temperature controller and DC relay to bypass thermostat
This plan is best if thermostats burn out frequently, and better than bypassing thermostat as shown above.
The PID or temperature controller is more accurate than mechanical thermostat, but heating water is dynamic, and the probe is reading temps off the steel tank ... and the probe and thermostat and element covered with insulation same as any electric water heater. Inkbird PID temperature controller .pdf
While the illustration shows thermostat probe at lower thermostat, it can be installed at top of tank on the upper thermostat if one chooses, and still control the solar power at lower element.

The Omron DC relay is made for switching high-amp DC and will function over 10,000s of operations, and reliably cut off solar power if temps exceed setting.
Omron relay spec sheet

The disadvantage of the temperature controller and relay are the cost of purchasing the relay and other parts as shown .... need for low voltage power supply (12-24 volt LED driver) ... needing enclosure for safe install of the power supply, relay and controller ... and lack of simplicity.

Buy:
Omron DC power relay
PID Temperature controllers
Digital temperature controller
12-24 volt DC IP67 LED driver
Bud industries hinged enclosure 6x8x4
Control high or low voltage DC using timer
-ST01 timer is battery-operated and rated for 120-240-277 volt AC or 12-24 volt AC or DC
-Omron DC relays have a AC or DC coil depending on model selected, with a maximum rating 200 amp DC depending on model selected.
-LED drivers produce 12-24 volt DC voltage, ordinary doorbell transformers produces 12-24 volt AC
Buy from my affiliate links:
Omron DC power relay
Intermatic ST01c timer/ 1 year warranty
Ei600/ 5-year warranty timer
CR2 replacement battery
Waterproof LED driver
Resources:
Omrom power relay spec sheet
ST01C manual
Sell sheet with model numbers


Recommendations for lower element DC install
review techluck
Larger image
Local code requires direct bond (ground wire) from solar panel frames and metal conduit to nearby ground rod using #6 copper wire. Ground rod must meet local specifications.

Solar panels should be bonded to nearby ground rod, and bonded to water heater tank, and water heater ground wire connected back to main breaker panel that is connected to proper outdoor ground rod.

Connecting ground wires to metal water pipes is no guarantee of ground, and can cause deteriorated water pipe.

In addition to information above, solar PV power is DC, with a positive leg and negative leg. The negative leg of solar power should also be grounded, and this is not covered here.

Tapered drill bit for any size hole in metal
Drill 3/4" Hole into water heater for 1/2" conduit connection from solar
Buy
 tapered drill/ step drill bit for any size hole
Step drill bits at Amazon
Neiko tapered drill bit 1/4"-1-3/8 holes
safety switch

3 pole safety switch
3 pole non-fused safety switch wiring
120-240 Volt 3-pole safety switch
House power and solar power must have safety shut off to protect anyone working on water heater. Use fusable or non-fused. Clearly label, and locate safety switch next to heater. Local codes vary, and generally require another cut off for solar located outside near the solar panels
Connect all household & solar ground wires together
Buy:

3 pole 60 amp non-fused safety switch
3 pole 100 amp non-fused safety switch
30 amp AC cartridge fuse
20 amp AC cartridge fuse
30 amp DPDT shut off switch
Resource:
How-to-wire-safety-switch.html

1500 watt element

Wiring diagram for element and thermostat
You can use ordinary AC element for solar DC.
Use new element/ lower part of tank
1500 watt 120 volt element:
Buy:
1500 watt 120 volt element
Resource:
Read about / choose water heater element + how to clean out tank and replace element
30 amp DC safety switch DC safety switch
Heavy Duty 250 V Dc Voltage; 30-60 Ampere
Use 10 gauge wire with 30 amp fuse
Use 6 gauge wire with 60 amp fuse
Buy:
Square D 30 amp DC/ outdoor/ fusable/ HU361RB
Square D 60 amp DC/ outdoor/ fusable H222AWK
100 amp non-fusable/ outdoor/ at Amazon
100 amp 3-pole non-fused safety switch

Resource:
DC safety switches
How to wire safety switch
Convert AC water heater to DC water heater
DC relays for solar power
surface mount fuseholder Surface mount ANL fuseholder
Buy:
e2 fuseholder with platinum plating
ANL fuses
     
Fuseholder                         Fuse
Photovoltaic fuseholder/ DC fuseholder/ 1000 volts DC/
DC fuse/ photovoltaic fuse: use 20-25 amp fast-acting for designs on this page
Not waterproof... mount inside Nema 3R enclosure
Mount on din rail/ change fuse with flick of finger
Install 25-30 amp fuses
Use 10 x 38 DC fuses

Buy:
Photovoltaic fuseholder / DC fuseholder/ ultrasafe/ at Amazon
Ultrasafe fuseholders at Amazon
600 volt DC fuses at Amazon
Mersen 600 volt DC fuse
waterproof DC fuse holder Waterproof Solar fuseholder/ 1000 VDC/ 2 amp to 30 amp
Buy
Solar fuseholder at Amazon
Fuse holder plus 20 amp DC fuse
Fuse holder plus 30 amp DC fuse
DC circuit breaker
DC circuit breaker
DC circuit breakers for Solar/ use 20-25 amp for designs on this page
Buy from my affiliate links:
DC circuit breakers
High voltage DC circuit breakers at Amazon

Combiner boxes at Amazon

Resource:
How to set up solar array
Water heater cover
Larger image
1) Make sure thermostats are covered with insulation, protector, and cover. See image
Without insulation, Thermostat exposed to room temperature will misread temperature and cause overheating.
2) Make sure thermostat sits flat against tank wall. Wiggle thermostat. Check that bracket is not rusted and loose.

Buy:
Upper element terminal protector
Lower element terminal protector

Resource
Troubleshoot electric water heater

Misc notes and such that generally apply to higher volt installations:
100 watt solar panel
Back view                      Front view
Example Renogy mono-crystalline panel
Using PV solar voltaic solar panels:

Parallel means both negative wires are connected together and both positive wires are connected together.
Series means negative wire on first solar panel is connected to positive wire of next panel... etc.

If panels are wired in series, the volts are higher, amperage is lower, and resistance is higher. Resource with calculation. This is good for harvesting maximum power in low solar conditions. Series = good for low solar conditions (after 3 pm on sunny day or overcast day).
If panels are wired in parallel, the volts are lower, amperage is higher, resistance is lower. This is good for harvesting maximum power in high solar conditions. Parallel = good for high solar conditions (mid-day sunny conditions)
How to optimize solar panel array

Buy from my affiliate links:
One 100 watt solar panel $149
One 250 watt panel $350
Two 150 watt panels $300
Buy solar panels
Mounting brackets

Solar panels are like flashlight batteries.
Total wattage or power stays the same no matter series or parallel.
If panels are wired in series, the amperages stays same and voltage increases.  
If panels are wired in parallel, the amperage increases, and voltage stays same.
So 2 Renogy 250 watt panels wired in series will produce 60.2 volts and 500 watts.
2 Renology 250 watt panels wired in parallel will produce 30.1 volts 16.4 amps and 500 watts

On water heater, change lower element to 900-1200 watt DC, and disconnect wiring from top of heater.
Leave upper element in place and connected to 240 volt.
Upper element works in ordinary fashion when water heater is ON.
Lower element is ON when solar panels produce electricity.
Drawback of low voltage: long time to heat.
Other option: use same plan using smaller 20 gallon heater/ read: Under counter water heaters
Reliance water heater
Reliance/ 6-10 gallon/ Side connections/ 6 year warranty
Buy
Reliance water heaters
12-3 extension cords
12-3 Southwire cable>
Resources
Reliance manual
State manual

Example: If your panels produce 91 volts x 16 amps = 1456 watts (the 91 volts 16 amps will probably burn up the thermostat when direct connected to water heater so use high voltage plan).
If your 91 volts drops to 60 volts in the afternoon, then the wattage drops and element produces less heat

If you connect 1456 watt output to an element rated for 120 volt 900 watts, then element will probably burn up.
If you connect 1456 watt output to an element rated for 120 volt  2500 watts, then element will still produce 1456 watts heat.
If you connect 1456 watt output to an element rated for 24 volt 600 watts, then element will burn up.

If your solar panels generate 145 volts x 15 amp = ?
240 volt x 15 amps = ?
What happens when you connect 240 volt 15 amp electricity to 120 1500 watt element?
The element burns up.

Choose element rated for your output:
Ordinary elements work fine for AC or DC, but are not often available in low volt and watt ratings, so you need DC element.

Single U and double U DC elements, 24 volt 500-900 watts.
The single U has ordinary element style with 2 screws for connecting the wires. So your solar panels are connected directly to the element.
The double U element  has 4 screws for 4 wires and can accommodate two separate connections.... meaning you can have two separate sets of solar panels, and each set of solar panels can supply power to one of the U
3U elements are usually made for 3-phase boiler installations, have larger thread, and will not fit a residential tank.
Buy:
DC elements
Single U 24 volt 600 watt element
Double U element
single U element
double U element
Resources
Solar PV safety
How to set up array
How to replace water heater elements
Figure volts amps watts
All solar links
Convert AC water heater to DC water heater/ high voltage

What size water heater?
Typically in residential water heating, small water heaters (20 gallon) use 1000-1500 watt elements. Ordinary shower uses 10 gallons hot, ordinary bath uses 20 gallons hot.
You can set thermostat to higher temperature to get more miles out of a tank of hot.
http://waterheatertimer.org/Increase-amount-of-hot-water.html

Larger water heaters use elements with more wattage in order to heat the water....
A 500 watt element would struggle to heat a 40 gallon tank

5.866689  Kwh to raise 40 gallons of water 60°F (starting at 60- and ending at120°F)
Typical shower might be 104°F
1000 watts for 1 hour is 1 Kwh
Your 500 watt element produces 1 Kwh for each 2 hours operation
So you would need 5.867 x 2 hours or 11.73 hours to heat a tank ... and that is with ideal conditions, no consumption of hot during those hours, full sunshine, no cooling of tank etc etc ... except the tank would cool, and sun is not dependable each day.
.. or if you satisfied with less-than-thermostat-setting hot water, say 80°?
http://waterheatertimer.org/Kwh-temp.html
Din rail fuseholder
Install in-line fuseholder so circuit can be turned on.
Multiple fuses and breakers on same circuit are fine.
Buy:
Din rail fuseholder
10 x 38 mm fuse

Mersen DC fuseholder
Mersen DC fuseholders
Photovoltaic fuse
20 amp DC fuse

14 x 51mm fuseholder and fuse

Din rails

DC circuit breaker for solar panels








Buy
Tools
Milwaukee
DEWALT
Black and Decker
Stanley
SKIL
Makita
Porter-Cable
Bosch

Irwin Hand tools
Klein hand tools
Fluke electrical testing
Dremel hobby tools

Campbell Hausfeld air powered
Tekton automotive

Powerbuilt automotive
Saws and saw blades

Buy from my affiliate links every time/ thanks:
Amazon
''As an Amazon Associate I earn from qualifying purchases''
Enter Amazon from any link on my site, fill cart with any item ... purchases pay small commission

E-mail: geno03245w@gmail.com
My response might end up in spam folder, check email folders
Waterheatertimer on Twitter
Message thru facebook