Larger image |
Same
as above
...
maybe this diagram uses unecessary extra relay to do same job as above
This
wiring diagram does NOT by-pass water heater safety features
Specifications
for DC water heater:
For this diagram and diagram above, the specs call for:
Two or three G9EB1 DC-DC relays with 24 VDC coil/ rated 30,000
operations at 240 Volt 25 Amp DC
One 250 Volt 25 amp circuit breaker to match maximum rating for relays
One NO-NO relay with 120 Volt AC coil
One power supply
One 120 volt photoeye
One stock electric water heater with ordinary upper and lower
thermostats and ordinary 240 volt elements
Resources
How to add thermostat to gas or electric
water heater
How to wire thermostats
Commercial 180 degree thermostats
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|
 |
Purpose
of this illustration is inspire experiment by folks
who can avoid killing themselves
and damaging property
This
wiring diagram does NOT by-pass water heater safety features
Ordinary
elements work fine with DC
Ordinary thermostats burn out with DC
This wiring violates water heater safety code and voids water
heater warranty.
This wiring by-passes ECO thermal reset button located on
upper thermostat,,, because Solid state relays fail closed and not
open.... so in event of run-away heating caused by failed relay... the
ECO will not turn off the solid state relay.
This wiring is not guaranteed to work... it should work... but solid
state relays are never completely OFF.
Solid state relays can get very hot, and require heat sink.
Water heater thermostats must be covered with insulation to correctly
read water temperature through tank wall. Exposure to room air can
cause thermostat to misread temperature.
Relay must be located outside of tank because of high heat.
Thermostats are mechanical bi-metal switches... thermostats will work
with power coming from 12 volt DC transformer
ECO protected thermostat located at top of tank can be substituted
in place of lower thermostat... giving two ECO protected-thermostats.
Thermostats can be wired many ways. Illustration shows typical
non-simultaneous, where either upper element is ON or lower element is
ON or both elements are OFF. Both elements never ON at same time with
this illustration.
Buy:
60 volt 25 amp DC-DC solid state relay
100 volt 25 amp DC-DC solid state Relay
200 volt 25 amp DC-DC solid state relay
Relay safety cover
Heat sink
Electromechanical DC-DC G9EB-1 relay
Resources
Solid state relay data sheetSolid state relay DC relay data sheet |
 |
Same as
above except timer is located before the transformer
Turn off transformer at night when no solar is available
This
wiring diagram does NOT by-pass water heater safety features
Buy
from my associate links
60 volt 25 amp DC-DC solid state relay
100 volt 25 amp DC-DC solid state Relay
200 volt 25 amp DC-DC solid state relay
Relay safety cover
Heat sink
Electromechanical DC-DC G9EB-1 relay
Amico 120 volt 7-day timer
Dust cover for Amico timers
Amico
timers
Resources
PV water heater discussion of elements/ link
PV water heater discussion of elements/ pdf
Read research .pdf paper
Electromechanical relay vrs solid state
relay/ pdf
How to wire water heater thermostats
How electric water heater works
CN101 Amico timer manual/pdf |
Larger image/ amico timer with
dust cover
Dust cover |
CN101A
timer
Amico
timers
12 / 24 volt DC timer/ 120volt ac
7 day 17 on-off settings
12-24
Volt DC programmable timer
Buy:
Amico 120 volt 7-day timer
12 Volt/ 16 amp/ DC timer
24 Volt/ 16 amp/ DC timer
Dust cover for Amico timers
Amico
timers
Transformer: 120-240 Volt to selectable DC
voltage
Resources
CN101A/ amico timer manual/ pdf with wiring
How to wire amico timer
Terminals |
|
When voltage drops, then
wattage of element drops.
Element voltage and
wattage printed on end of each element. Element rated for 240
volt
4500 watt will operate at 1/4th wattage at 120 volt.
At 480 volts, the wattage is multiplied by factor of 4.
Overvoltage above element rating will burn the element out.
4500 watt @ 240 Volt will heat about 21 gallons per hour
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|
DC-DC
Solid state relays
3-32 volt input > choose 60-220 volt DC output
No arc. Quiet operation.
Turns power off by reducing voltage/ power is never completely stopped
Buy
from my associate links
60 volt 25 amp DC-DC solid state relay
100 volt 25 amp DC-DC solid state Relay
200 volt 25 amp DC-DC solid state relay
Relay safety cover
Heat sink
Resources
PV water heater discussion of elements/ link
PV water heater discussion of elements/ pdf |
 |
Use
Hour meter
240 volt hour meter connected to upper element.
12 VDC hour meter connected to lower thermostat
Requires one 240Volt hour meter and one 12-24 volt hour meter
Buy:
UWZ48E-240V AC hour meter
Intermatic
bezel to support UWZ hour meter
Intermatic
ac hour meters
240 volt hour meter
Intermatic GZ series 10-80 VDC hour meter
Intermatic
FWZ53-24U
12
volt DC hour meters
How
to read hour-meter results:
Wattage
of element must be determined
Use multimeter to check voltage of water heater
Look at label on side of tank for different wattages at different
voltages
Lower voltage means lower wattage than shows on element.
Confirm element wattage printed on end of each element
For example 4500 watt element and 240 volts
Hour meter reads 6 hours
4500 watts x 6 hours = 27,000 watt hours
27,0000 divided by 1000 = 27 kilowatt hours
With photovoltaic DC... the actual Kwh may not be calculable, and the
data less useful |
 |
Thermostats,
elements and wiring resources
Buy:
Camco
90F to 150F ordinary thermostats
Camco 120F to 180F thermostat (commercial
grade only)
Camco 180F lower thermostat
(commercial
grade only)
Therm-o-disc upper element plastic terminal
protector
Therm-o-disc lower element plastic terminal
protector
Resources
How to wire water heater thermostats:
How to wire off-peak water heater thermostats
How to wire two water heaters
How to replace thermostats
How to replace elements
How to test elements
How to select right wire and breaker
|
Ordinary
water heater elements will work with DC power
Quote: "Here is another way to look at it:
If
your element is designed for 240 volts AC, then applying 120 AC or DC
volts to it is unconditionally not a problem (unless it is not in
water, of course.)
At 240 volts, it will pull about 4.17amps.
Successfully applying 480 volts AC to it will destroy it.
This means you can
use AC-rated element
But
if you have a panel whose Vmp is 480 volts and whose output power is
1000 watts, its Imp will be 2.28 amps, and its Isc will not be much
higher, lets say 2.5 amps.
Now if you connect that panel to the
heating element, you will not be in any danger of burning out the
element, because it will be able to pull at most 2.5 amps from the
panel, and the panel voltage will be less than 240 volts at that time.
It
is a somewhat odd statement, but absolutely correct that if the panel
maximum output power does not exceed the power rating of the heating
element, then there is no combination of panel current and panel
voltage that can damage that element. However, different combinations
of panel specifications and heater specifications will determine
whether most of that potential maximum power actually ends up in the
heater or whether it is wasted because the panels are running far from
their MPP.
Just don't try it with batteries, generators, or
power supplies because, unlike solar panels, they can be damaged by
attempts to draw more than their rated power from them and they could
damage the heating element while trying!!!
|
Previous
emails contain the calculations of
what I expected to be the ideal number of series PV panels (Unisolar
64Watt) for the 4500W element in order to maximize yield aka (MPP)
maximum power point. That number of panels (and
thus PV
impedance) for this experiment equipment was calculated to be very
close to 3 panels in single series string (or 2 strings of 6
each). Other PV panel models have various Vmp and
Imp
specifications (and thus different impedance). Other water
heaters may have different heater element wattage (resistance) and thus
obtain different results.
Procedure: Array was put into various configurations and then the DC
amps and volts under element load were measured. |
Calculations:
Vm = Volts Measured
Am = Amps Measured
Wc = Watts Calculated = Vm * Am
Wpv = Watts PV name plate rating of the array
EF = Efficiency Percentage = Wc / Wpv
PV panels in single series string.
1 pv panel Vm=19.41 * Am=1.0, 19.41Wc /
64Wpv = 30.3% EF
2 pv panels Vm=34.75 * Am=2.5, 86.87Wc/
128Wpv = 67.8% EF
3 pv panels Vm=44.30 * Am=3.9, 172.77Wc / 192Wpv = 89.9% EF
4 pv panels Vm=49.03 * Am=3.6, 176.50Wc / 256Wpv = 69.9% EF
5 pv panels Vm=52.62 * Am=3.9, 205.21Wc / 320Wpv = 64.1% EF
6 pv panels Vm=53.97 * Am=4.1, 221.27Wc / 384Wpv = 57.6% EF |
6 pv panels (2 parallel
strings, 3 panels per string)
Vm=53.55 * Am=4.2, 224.91Wc / 384Wpv = 58.5% EF
Conclusion:
3 panels of US64 is the ideal number in single series string for 4500W
element as per calculations:
Its looking possible to calculate the appropriate number of panels in
series to match the resistance of heater element.
Paralleling ideal number in series does NOT double output. |
There are lots of
different types of PV systems. Type 2 and 3 are most common.
1) Off-Grid DC Loads.
Sun -> PV Array -> Charge controller -> Battery
Bank -> DC Loads
2) Off-Grid AC Loads (this is what my system is, Outback VFX).
Sun -> PV Array -> Charge controller -> Battery
Bank -> Inverter -> AC Loads
3) Grid Tie Battery-Less
Sun -> PV Array -> GridTie Inverter -> AC
Mains/Grid
4) Grid Tie with Battery Backup (example Outback GFX)
Sun -> PV Array -> Charge controller -> Battery
Bank -> Grid-Tie Inverter -> AC Mains/Grid and AC Loads
Techluck would also be a separate type in my opinion.
Type 5) Techluck, Battery-Less
Sun -> PV Array -> DC to AC Converter Box (non 60Hz)
-> Resistive Load
|
Adapter kit can be used or
better idea is to use PV combiner. But the combiner is more
money.
Our DC Water heater system is Type 6:
Type 6) Direct Power DC Loads, Battery-Less
Sun -> PV Array -> DC Relay -> Resistive Load
The main advantage to type 6 is:
No electronics to fail
No Heat sink to waste power
No Batteries
No Inverter
No Lightning protection needed
No Charge controller
This
eliminates much of the upfront equipment cost and also the maintenance
cost / time of that equipment. No moving parts for
PV or
electric water heater, they go well together |
|
Rules
of thumb
|
Here is the first rule of
thumb:
Match element load in Ohms to approximate 40% more than Vmp divided by
Imp.
( Vmp and Imp are found on the spec sheets of the solar
module) |
Simple
answer:
Start with 4500 Watt element. Why?
a) It comes with most heaters so you already have it
b) It has good power handling ability (at least 4500 watts!)
c)
Have the option to work down one step (5500W with lower ohms) or up a
few steps (3800, 3000W with higher ohms) in resistance IF NEED BE to
match your designed PV array impedance.
Element size
(resistance) needs to have an approximate match to the PV array
(Vmp/Imp) * 1.40 so there are a few ways to do this:
1) Jigger
the number of panels in the PV array. If you keep adding more
and
more individual panels per string you increase Vmp and therefore
increase PV impedance.
2) Jigger the configuration
(series/parallel) in the PV array. If the PV target
resistance is
too high make more strings with what you have. This will
increase
Imp and decrease the PV impedance.
Example: 12 panels can be put into 6 different configurations:
one string of 12 panels
two strings of 6 panels
3 strings of 4 panels
4 strings of 3 panels
6 strings of 2 panels
12 strings of 1 panel.
These different configuration give VERY different PV impedances.
3) Use a different element wattage (resistance). Make sure
that PV array wattage < element wattage.
4)
If you haven't purchased the panels yet and your design isn't working
out consider buying a different model of PV panel that has different
Vmp and Imp specifications.
|
I have
TWO favorites.
For
a small system for a user that does not require a lot of on demand
stand-by hot water the "Simultaneous DC water heater" will work well.
http://waterheatertimer.org/images/Thermo-o-disc-upper-thermostat-Non-simultaneous-DC-panels2.jpg
Its
the one with the Grid powered upper tank, PV powered lower
tank. The grid does not turn off the PV. Relays are
high
powered DC-DC
Advantages:
-Uses one tank
-Simple
Disadvantages:
-Limited grid-powered hot water on demand (upper part of tank)
-Somewhat limited pv-power storage capability (just lower part of tank)
-One relay only so some wasted power on cloudy days compared to two
element model.
-Using NG or Propane to heat water on cloudy days not an option.
I like the option of adding timer so it just runs on PV during the day
|
For a
large system or one that has
space for two tanks the "Series wiring diagram" with TWO relays is my
favorite.
http://waterheatertimer.org/images/solar-insolation-adaptive-system-series-120V-upper2.jpg
There
needs to be some way to show that this electric water heater is fed
into a second NG, Propane or Grid Electric water heater.
Advantages:
-Solar adaptive to have high efficiency during sunny and cloudy weather.
-Two water heaters means lots of gas or grid powered stand-by hot water
in the times of bad solar.
-Separate water heaters means lots of PV hot water storage ability.
Disadvantages:
-Two tanks needed
-More complicated wiring
-Need to adjust photo eye so it switches system between high / low
properly.
Only
problem I see with the diagram is that both elements should be same
wattage/resistance. Don't need the wattage, Low watt, High
watt
labels. System can be designed with any number of different
elements according to PV size, etc, so doesn't need to be on the
diagram. |
There
needs to be some way to
show that this electric water heater is fed into a second NG, Propane
or Grid Electric water heater.
Ok will make drawing... page edit and
this illustration are next
Jan 2015 |
|
Omron relay discussion:
|
Our target for this water
heater is
250VDC
* 18 amps = 4500 watts. 250VDC/18amps = 13.8 ohms |
Conclusion:
Relays should last many years of daily use/ 5 to 10 years |
Lightweight DC-DC relay: in stock $129
http://www.onlinecomponents.com/keywordsearch.aspx?text=G9EB-1
Heavy-duty: 13 week delivery / in stock
$286
http://www.onlinecomponents.com/keywordsearch.aspx?text=g9ec-1
***************
$129 DC relay is cheaper than spending
$170 for 90 amp 3-pole AC contactor
And rated for DC so its way better.
^^^^^^^^^^^^^^^^^^^
The full-solar water heater has two
relays/
Can you give rough estimate what you
think lifespan of the relay will be?
.... spec sheet shows minimum 30,000
operations at 250 VDC at 25 amp?
So 30,000 operations at 250VDC * 25 amps = 6250
watts. 250VDC/25amps =
Impedance 10 ohms.
Starting to get in the ball park. 6250 watts of pv power is a
little high to be dissipated from the 4500 watt element.
Perhaps if we use the example of 250VDC
* 18 amps = 4500 watts. 250VDC/18amps = 13.8 ohms
would be a realistic large PV direct powered water heater example.
So I guessing we will get about 40,000 operations instead of only
30,000. Not a big increase but whatever.
.... can carry short term 40 amp for 10
minutes, 50 amp for 5 minutes
Yes. Probably the max rating on the lugs of the dc
relay. Not a big deal for our use.
.... our solar water heater might turn
on-off 30 times per day on a party-cloudy day.
I disagree and agree. The full model of our design uses two
relays One relay turns off the array when the
water
heater reaches max temp. On my solar powered water heater the
on/of relay#1 may only operate typically maybe twice in a day.
It comes up to temp on a sunny day. Turns off.
Maybe it bounces once more as water is used in the afternoon.
Lets assume 2 open operations per day. 40,000 / 2 /
365 = 54 years.
Relay#2
that controls the shift between high and low power may only change
state once or twice (sunny day: low sun->high sun->low
sun).
or
many many many times on a cloudy day when clouds pass
by.
This is where a delay timer comes in to prevent the flapping between
high and low sun states.
Lets be less than optimistic and assume the average is 20 times a
day. 5.4 years.
But! The longevity of the second relay is helped
out by one thing.
In our design the second relay that controls the high / low solar state
does an open operation when going from low solar state to high solar
state.
In the "low solar state" both upper and lower elements are in
series. When they are in series in high sun the yield is not
going to be very good because its not going to hit the power curve at
the right spot.... Thus we want to shift to "high solar state" with
only a single element in the circuit. But what is the current
and
voltage flowing through the circuit? Crappy! and because its
crappy its electron flow is easier to break. I would expect
maybe
a 2x longevity of the relay. Take the 5.4 years and
double
that to 11 years.
Now it doesn't look so bad does it?
.... will the solar water heater exceed
250 VDC at 25 amp?
No
thats 6250 watts. I don't think someone should build an array
that big and try to dissipate the power into a 4500 watt element.
.... how often will the solar water heater run at
30 amp instead 26 amp
I don't think the amps will go that high. 18 amps for a 4500
watts of PV array would be more typical.
****************************
If the relays burn out once per year, then the cost of heating water is
$260 per year.... 65% cost of using ordinary 240 volt electric
If we use the heavy duty DC-DC relay, the cost to replace relays could
be $600 per year.... 150% cost of using 240 volt electric
I dont
think they will burn out nearly that fast. I would
still
get the biggest relay I could afford because a relay is cheap compared
to PV panels. 4500 watts of PV is $4500 give or
take.
Will the solar water heater fill tank
with hot water if constrained by 25 amp 240 volt breaker?
I
would derate the breaker by 0.80 because the load is considered
continuous. So 25amps will handle a 20
amps load.
I
would also size the breaker up by a factor of 50% to handle the edge of
cloud effect. Then once the calculations are done take the
next
highest breaker size (round up).
Some
of my panels put out 8 amps. I have 15 amp breakers on those
strings. The wire is 12awg so everything is well
protected
by the 15amp breakers.
Do you think the breaker will
sufficiently protect the DC-DC relay from overclocking?
What do you mean by overclocking?
Running more amps than rating on DC
relay
I'm trying to recommend a circuit
breaker, based on what is available.
I see 150 volt 20 amp ....
https://www.amazon.com/dp/B004EQK8SA/?tag=waterheaterti-20
If we recommend 150 volt 20 amp
breaker....
Will this heat enough hot water?
Depends on use and size of PV array. Amps depend on
Ohms of heating element.
Maximum size system would be about 4500 watts PV
4500 watts of PV on a sunny day will give about 4500 * 5 rule o thumb =
22.5KWh.
Thats a lot of hot water. Like 150 gallons or
so .... ON A SUNNY DAY.
What size tank do you estimate?
Depends on use and size of PV array. Bigger =
better as long as the tank is cheap.
Storage is not wasted energy.
Even if I had a small 1500 watt array I would still buy the biggest
tank I could afford.
If we have 150 volt DC @ 20 amp max///
How many 250 watt solar panels do you
think?
Still 2 strings with 7 panels each
Oh
I see what you are saying. Using a 4500 watt array with 4500
watt
heater elements (12.8ohms) we will be higher than 150 volt rating on
breaker.
Assuming 4500 watts PV with 4500 watt element.
12.8ohms * 1.4 = 18ohms target PV impedance
285VDC/15.8A = 18ohms impedance
285VDC * 15.8A = 4512 Watts PV
15.8A * 1.25 for continuous. 20 amp breaker is ok but .....
We need a breaker that can handle 285VDC. Hmm Maybe
*gasp* fuses would be ok.
Damn. I thought we had all the parts figured out :)
Are
you trying to present and example to people? What is the size
of
the array you are targeting. Certainly not one size fits
all. I recommend we figure out parts for a large 4500 watt
system
and if user doesn't want something that big they just down scale the
size of the array. Everything else will still
work.
Otherwise you will have to spec out small (1500) medium (3000) large
(4500W) sized systems. |
In
our design the second relay that controls the high / low solar state
does an open operation when going from high solar state to low solar
state.
In the "high solar state" only the lower element is in
series. The upper element is bypassed by the upper
relay. When we want to shift to "low solar state"
we open
the upper DC relay to put the upper relay in series. We only
do
this when the solar is low. Maybe 300 mW/m2 or
less. This results in less current to break and
less wear
and tear on the DC relay. I would expect maybe 3x the
longevity
of the upper relay or more. Take the 5.4 years and
triple
that to 15 years.
Yes good point.
I will add that detail.
My estimate is still $4-5000 to build... and $260-$215 per year
operation, repair and depreciation |
Resource:
Following link has detailed information about DC
http://waterheatertimer.org/pdf/DC-circuit-breakers-read.pdf |
