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Heating water with excess power
#11
One of the down sides to doing it with ac elements is if the available solar is below the amount the hotwater heating element is using then the battery volts would drop out of float because power would be used from the battery and shutoff the aux signal to the relay till the battery raises back to float again. On a day there’s not much available pv due to clouds then the relay could be kicking on/off a lot.. doing it with dc elements would just divert the excess and the element would use only the amount of power diverted to it.
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#12
If you're going to use AC for heating, I think you need some sort of microcontroller with a logic that takes into account:
* battery SoC (Is it near full?). Can probably use one of the MX60 outputs
* real time power output of the GTIL2 (Is there enough excess capacity to power the heater?). Can be fetched from IotaWatt.

If using DC for heating, you only need the battery SoC, so could probably use just the MX60 output
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#13
It appears that the diversion of PV isn't allowed via the OB because PV is routed though the controller. my bad
"External DC sources (wind, hydroelectric) are directly connected to a battery bank" missed this part
later floyd
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#14
(08-31-2020, 02:25 AM)Korishan Wrote: I believe, not entirely sure, that once the charge controller (as the FM60 above) detects current loads on the primary output (aka to the battery), then it turns off the Aux port and allows all power to flow to the primary output.
If it doesn't detect it, then it probably monitors voltage very closely and when a heavy load happens on the inverter side, that causes the battery voltage to drop enough that the controller will switch over to primary feed and turn off the aux

I don’t think the aux is actually for diverting the current. The aux just sends a low voltage signal that can trigger a relay.
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#15
From the MX60 Manual:
https://www.altestore.com/store/media/pd..._rev_7.pdf Page 12 Wrote:AUXILIARY OUTPUT ( AUX + / AUX - )The Auxiliary output system uses the AUX + and AUX – terminals and is able to be programmed through the MATE to do a variety of tasks. The default use for these terminals is to drive one 12-volt fan for external cooling. The power available at these terminals is 12 VDC at 0.7 amps (8.4 watts) maximum.  These terminals should not be connected to any type of DC load which has a high inrush current requirement.  The FX includes internal electronic overcurrent protection for this 12 VDC output circuit which auto resets if it is short circuited.  No additional fuses are required.  Use the OutBack FX Turbo Kit or DC12-FAN for cooling.  For automatic or advanced generator start functions, the Auxiliary Output can drive a 12V automotive relay for the 2-wire starting circuitry of a generator.  OutBack Power Systems does not support 3-wire start generators, however, a 3-wire to 2-wire conversion kit is available from a different source.

and from the FM60 Manual:
http://www.outbackpower.com/downloads/do...manual.pdf Page 30 Wrote:The AUX (Auxiliary) is a secondary control circuit — essentially, a small power supply that provides a 12 Vdc output current (up to 200 milliamps / 2.4 watts) to an isolated load. It is either ON (Active High) with 12 Vdc available at the output or OFF (Active Low) with 0 Vdc at the output. It can also be set to AUTO, so that it activates when certain criteria are met. The AUX output can respond to specific criteria and control cooling fans, vent fans, load diversion, fault alarms, and automatic generator control. In some cases, such as the PV Trigger, Night Light, or Diversion:Relay applications, the polarity of the output can be reversed so that a lack of power activates the output. This function is controlled through the Aux Polarity screen in the ADVANCED MENU. (See page 56.) NOTE: Diversion:Relay and Diversion:Solid St can be used for AC coupling applications. The AUX output can also be controlled externally through the system display. See the literature for the system display (if used) for details.

So with both of these, you can use a relay to trigger other devices. This would work for dealing with diversion control. Considering that they are activated with "certain criteria", including diversion control, it should be easy to configure this option.
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#16
Simplest is to use my design with a controller that turns on a heating element powered by the battery when you deem the battery to be above 90% or whatever. Or when the solar voltage is above its maximum tracking point. Then you know you have excess power.
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#17
Using the graph I showed earlier (from daromers video), you could just as easily use a DC element instead of an AC element and power directly from the batteries instead of the inverter.

If you don't want to alter your existing water heater, you could do a pre-heater setup. This would use a second water heater tank that is plumbed "before" the existing system. This one would have the elements replaced to use DC elements. If it's not used, there'd be no difference between it being not used and be cold water, or it not being there at all, as cold water would enter your primary tank just as usual.
The pre-heater tank could be much smaller, too.
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#18
I like daromer's idea of using the array voltage & when this rises above max power point voltage, it means you have spare energy. As soon as the array voltage drops to MPPV again, it would cut off again.
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#19
Using a preheater tank. Let’s say main tank cooled to 100 degrees over the night. When a shower is started hotwater will come from preheater tank to main tank. The preheated water will begin to warm the main tank but that will take a while. The first couple people showering will have water that is only 100degrees or slightly warmer from the little bit of preheated water that has come into the bottom tank that mixing with the colder bottom water during the duration of the shower.

Right now I wait till battery is full and then I start the AC hot water heater and fully heat the tank. I do this when no other loads are on (actually like 300w are still on) so it’s all free water heating but the battery Are still drawn from when available pv power is lower than the 3000w ac element. The water in the tank is almost completely full of tap cold water each day once showers are done. Right now I only heat the entire tank once. I’d assume using the preheating tank would make the entire main tank as hot as the preheater tank temp settings but only once everyone has showered because it would take that much flow to put the preheated water into the main tank. Then the main tank would cool over the night, maybe to 100 degrees. And then the first couple showered will only be with close to 100 degree (or whatever the tank cooled to overnight) water.

The preheater tank would keep the main tank from running as much as it would if preheater tank wasn’t installed. But for the first couple people showering it would only be as hot as the water cooled to overnight. Unless I keep the main tanks power supply on all night to keep the tank up to temp at night but then I’d be using battery or grid power for that, which doesn’t work cause only excess pv should be used.


Without a preheater. Using a dc element in the bottom of my existing tank. If there wasn’t enough excess pv that day due to clouds or to many loads. Then the bottom element wouldn’t have heated the water. Then I’d need to turn on the hotwater heater to have hotwater and if the bottom element being dc means that I can’t fully heat the tank. I’d need to fully heat the tank because that’s just enough hotwater for the whole fam to shower. If I kept the ac power available to the top element- hotwater heater 24/7 then the tank would turn on at night when someone showered, which would drain the battery.
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#20
(08-31-2020, 06:53 PM)Cheap 4-life Wrote: Using a preheater tank. Let’s say main tank cooled to 100 degrees over the night. When a shower is started hotwater will come from preheater tank to main tank. The preheated water will begin to warm the main tank but that will take a while. The first couple people showering will have water that is only 100degrees or slightly warmer from the little bit of preheated water that has come into the bottom tank that mixing with the colder bottom water during the duration of the shower.

Not entirely so. The preheater tank regardless of temp wont change the temp of the main tank. The way cold water is introduced into the hot water tank is to make it not dilute the hot water as the cold water replaces what was used. As the cold water level rises on the bottom of the tank and passes the lower thermostat, it triggers that element to turn on (altho, it's not enough to heat the water on its own and will eventually be overloaded by cold water)
A preheater tank would basically be turning an 80gallon tank into 120 (if using a 40g preheater tank, for example) tank. It would extend the run time of hot water.

So yeah, what ever the main tank cooled down to overnight, that's what they'd get. You could put extra blanket material around the tank to extend temp longevity.

(08-31-2020, 06:53 PM)Cheap 4-life Wrote: Right now I wait till battery is full and then I start the AC hot water heater and fully heat the tank. I do this when no other loads are on (actually like 300w are still on) so it’s all free water heating but the battery Are still drawn from when available pv power is lower than the 3000w ac element. The water in the tank is almost completely full of tap cold water each day once showers are done. Right now I only heat the entire tank once.  I’d assume using the preheating tank would make the entire main tank as hot as the preheater tank temp settings but only once everyone has showered because it would take that much flow to put the preheated water into the main tank. Then the main tank would cool over the night, maybe to 100 degrees. And then the first couple showered will only be with close to 100 degree (or whatever the tank cooled to overnight) water.

Since you heat the water with solar/battery, why not switch over to using DC elements anyways. You'd save efficiency conversion. Save energy from being wasted by going through the inverter. Unless your water heater is a long run from the battery.

(08-31-2020, 06:53 PM)Cheap 4-life Wrote: Without a preheater. Using a dc element in the bottom of my existing tank. If there wasn’t enough excess pv that day due to clouds or to many loads. Then the bottom element wouldn’t have heated the water. Then I’d need to turn on the hotwater heater to have hotwater and if the bottom element being dc means that I can’t fully heat the tank. I’d need to fully heat the tank because that’s just enough hotwater for the whole fam to shower. If I kept the ac power available to the top element- hotwater heater 24/7 then the tank would turn on at night when someone showered, which would drain the battery.

What you could do is do some replumbing of the heating elements. Something I've thought of before, tho not sure if it'd really be to any advantage. You'd take the elements out, put a piece of piping with a T at the bottom, and put the element down there. Turning on the element would cause water convection and the whole tank would get hot as it circulated.

Kinda like this:
 

Would be interesting how well it'd work. I suppose it depends on the demand, too.
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