FM80 AUX set points for AC Hot water Opportunity Load

pyintheye · March 2015

Hi to all

I am wanting to determine reasonable (STARTING) set points and the WHY of them to run a 240 volt 3000w H/W tank without frying any Equipment.
Hoping someone has a similar size system and is doing this already.

THX TT

BB. · March 2015

Assuming you have a 240 VAC inverter (or a 120 VAC heating element and 120 VAC inverter--just run longer for same amount of hot water):

3,000 Watts * 1/0.85 inverter eff * 3 hours per day * 1/48 volt battery bank * 2 days storage * 0.50 maximum discharge = 882 AH @ 48 volt battery bank

Rate of charge for system 5% to 13%, use 10% minimum for daily use:

882 AH * 58 volts charging * 1/0.77 panel+controller eff * 0.10 rate of charge = 6,644 Watt nominal array (based on battery bank size and 10% rate of charge)

Then how much sun... 3 hours a day minimum?

3,000 Watts * 3 hours per day * 1/0.52 system efficiency * 1/3.0 hours of sun per day minimum = 5,769 Watt solar array "break even" on 3 hours of noon-time equivalent sun per day

Depending on when you need the hot water (summer/winter) and your average outside air temperatures... When the outside air is over ~55F, you could look at using a Heat Pump type eater heater... They are around 2x as efficient as pure resistance heaters. However, they do output cold/dry air--May not be good in northern climate.

That is the basics using "nominal" numbers and guessing at hot water usage per day.

Obviously, if you want to only make hot water when the sun is up--You could downsize the battery bank and solar array. If you you use a genset during poor weather, that can down size the array too.

-Bill

waynefromnscanada · March 2015

BB. wrote: »

Depending on when you need the hot water (summer/winter) and your average outside air temperatures... When the outside air is over ~55F, you could look at using a Heat Pump type water heater... They are around 2x as efficient as pure resistance heaters. However, they do output cold/dry air--May not be good in northern climate. -Bill

Learned from a friend involved with retailing heat pump water heaters here in Nova Scotia, that these units tend to turn the area in which they're installed, into a refrigerator. They've had to install duct work to bring in outside air to feed the heat pump, then expel the cold air from the heat pump back outside. OK during Summer, not good at all during Winter. Pity.

pyintheye · March 2015

Thanks BB, Wayne.
So I'm thinking I have not asked the right question or have not been clear enough on my intent.
The 240V/3000W H/W Tank is set up as a recirculating preheat for the main propane H/W tank.
While I have been reading all the forum info on this topic for sometime now I still am in the dark as to how the AUX triggers, and in what order, relative to the AUX FLOAT screen and the AUX Low Battery Disconnect screen.
Since I have been spinning my wheels for 8 days with no Aux ON, I figured just follow the Manual on Aux SSR Diversion and see what happens.
I HAVE NO IDEA IF THE VALUES I PROGRAMMED THIS MORNING ARE EVEN CLOSE TO BEING RIGHT.

Absorb - 59.2V, Float - 52.8V, EQ - 62.0V These are Trojan Specs.
AUX mode - AUTO
HOLD - 15sec
DELAY - 5 sec
RELATIVE VOLTS - .2V, HYS - .3V
LOW BAT DISCONNECT - Time - .003, Dis V -53.0, Recon V - 56.0

The SSR is a Crouzet GN 84137020, Zero crossing, 50Amp

In the different discussions there is mention of PWM and setting the WIDTH, is this a Classic CC setting only, or is this in the FM80 somewhere?

Yesterday with pretty good sun, W/D on @ 41Amps, I activated the AUX manually to see how the Magnum Inverter was going to react to a near overload condition as the 3000W tank and laundry pair on should take it there. No shutdown, No Blue smoke but still over the 4400W rating for the inverter.
The AUX on screen was showing 100%. Is this Adjustable some how to lower the wattage going to the element and keep the Inverter in a safe working range.

Waiting for sun to see if it all works.
TT

BB. · March 2015

I don't know anything specific about the Outback system, but I wonder if you have a long enough time for the low voltage disconnect?

System goes to "float", then turn on water heater, if voltage below (whatever you like, but lets say 50.8 volts = ~12.7 volts or the point between charging/discharging) for >5 minutes, disconnect. This allows you to draw significant power from the battery bank without it dropping after a few seconds below 53 volts.

-Bill

pyintheye · March 2015

Well I waited all morning to see what would happen at the settings I put in.
The batteries charged all the way through the Absorb for the recommended 90 minutes. At that point the CC"s shut down and the voltage dropped fairly quickly to 55V. No current flow from either CC as the screens said CHARGED, stayed that way for 10+ minutes as the voltage slowly dropped from 55V to 52.8V. The CC screens went to FLOAT and a few minutes later the AUX did trigger with a load at around 73A. It took no time at all for the voltage to drop and trigger the BULK mode in both CC's. Soon as the FM80 showed BULK the AUX shut down.

I'm not understanding why the LBCO settings had no apparent influence in triggering the AUX load.
Please, what am I missing here?

TT

FM80 AUX set points for AC Hot water Opportunity Load

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