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Old 06-26-2017, 01:27 PM   #1
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Controller for prioritizing power to various loads

Is anyone familiar with a controller that will send power to various loads depending on the priority that you program? For example, power from the solar panels will be dumped into the battery bank, but then when they go into float the power is then diverted into the electric water heater (via the inverter), without drawing down the house bank.
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Old 06-26-2017, 02:29 PM   #2
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I don't know of any device that will do what you want. It isn't simple. After the batteries reach float via solar charging you could produce AC power from an inverter to heat hot water, but unless you had a really big solar panel system, you would almost certainly be drawing down the batteries.

Best do it manually. I have a boating friend who does this. He replaced the 120V electric element in his water heater with a 240V one which drops the wattage from 1,500 to 375. He has 400 watts of panels, but even a 375 watt draw is more than his solar panel system normally can provide, so he has to watch it and turn the water heater off if it clouds up and make sure that there is enough sun to fully recharge his batteries after the water heats up.

The point is, he can only do it with reduced water heater wattage, full sun, large solar panel system and careful monitoring. Not something a controller can do easily automatically.

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Old 06-26-2017, 02:42 PM   #3
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Actually, RV's have had them for years now. They call it "power/load shedding".
Here's an example.
www.precisioncircuitsinc.com/wp-content/uploads/2014/08/PCSOwnersManual.pdf
and their website.
120V Energy Management | Precision Circuits Inc.
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Old 06-26-2017, 02:48 PM   #4
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Excess load dump.

I think the traditional Xantrex/Trace SCs have that feature.

Should be standard for hybrid controllers that work with both hydro or wind and solar.

Alternative would be a battery monitor that could flip a relay open once SoC reached a predetermined point.

Don't have to wait for 100%, very little amps are being accepted by a lead bank after 85-90%.

I've heard of people running ice makers, heating water, charging secondary batteries.

Curious what other ideas people may have.
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Old 06-27-2017, 06:31 AM   #5
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but then when they go into float the power is then diverted into the electric water heater (via the inverter), without drawing down the house bank."

No need to involve the inverter , the resistance element of a HW heater will still heat the water with lower voltage.
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Old 06-27-2017, 01:42 PM   #6
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A cheap way is to use a voltage sensitive battery combiner. I have one on my fridge and on a ventilator fan. Yandina was source for the fridge and Ebay for the fan. When I am away they only run when there is a charging source over 13 volts from solar.
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Old 06-27-2017, 02:21 PM   #7
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But the point is when you may or may not have enough solar, you don't want to connect the non-essential loads until you're sure the bank's going to get to full.

Can't base that on voltage, only SoC or declining amps.

What you're talking about is good for LCD preventing loads from pulling a bank down too far, but ideally has adjustable setpoints.
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Old 06-27-2017, 04:20 PM   #8
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Some wind generators have controllers that dump excess energy to resistive banks.
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Old 06-27-2017, 04:58 PM   #9
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I live in s florida. There's always enough solar...

seriously, I agree it's not ideal for someone who needs true load management. But it works well. I found that for my needs it was almost perfect-for $70 cost. I have an unattended boat on the hard while I'm working on it . the batteries stay fully charged and my drinks are always cold when I arrive. The turn on point for the fridge is 13.1 volts. Fridge is set to 40 degrees and I keep it full of drinks. 180 watt solar panel produces an excess of power for the fridge and fan. The fan only draws .3 amps and would shut off if battery voltage reached 12.1 volts. The only other load is a small automatic bilge pump which deals with rainwater from cabin leaks.

I went to this arrangement because the two 8d batteries are on their last legs and the fridge was draining them dead if allowed to run at night while I was away for weeks. I doubt these batteries have 25 amp hours between them. Putting the combiner in the battery circuit has functioned well for a year. This has allowed me to delay battery replacement until I'm ready to launch. And still have use of all onboard electric. When I'm aboard working I just switch the combiner to always on and drop the temp on the fridge to the safe point for whatever I need to store.
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Old 06-27-2017, 06:12 PM   #10
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Could also just use a timer so the fridge only runs between 10am and 5pm.

Neither solution really directly applicable to the OP goal, without other assumptions.
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Old 07-24-2017, 04:22 AM   #11
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I've been thinking about this, and a desire to stay away from anything microprocessor controlled. Seems like the simplest solution would be:
  • Connect the critical 230v loads (fridge, security) to a small dedicated inverter;
  • Run a second inverter for normal house loads (microwave, waterheater, etc., perhaps 2kW or larger);
  • When leaving the boat, disconnect the battery feed to the larger inverter, leaving only the solar panel feed into it;
  • The battery charger will remain connected to the panels as well;
  • Ensure that the water heater does not switch on until the battery bank enters float, thus in the morning and early afternoon all solar power is dedicated to charging;
  • This can be ensured either through a timer on the waterheater, or perhaps a relay that triggers from a signal from the charge controller.
Thoughts?
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Old 07-24-2017, 09:17 AM   #12
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Almost all such devices are microprocessor controlled.
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Old 07-24-2017, 10:47 AM   #13
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I looked at this for my home generator. They're called load-shedding devices. The idea is, you prioritize your loads and lower-priority loads are shed when higher-priority needs max out the generator capacity.

It would be a perfect solution for home or boat generators, but they seem to only make them for large industrial installations. A business opportunity perhaps?

On the other hand, it seems installers of generators make more money if they can sell you an oversized unit which can power all your circuits, at their maximum rating, simultaneously. Never heard of any boat or house that could actually USE all that power at once tho.
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Old 07-25-2017, 06:34 AM   #14
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"I looked at this for my home generator. They're called load-shedding devices. The idea is, you prioritize your loads and lower-priority loads are shed when higher-priority needs max out the generator capacity."

ANY relay 120v that can be set as a NO or NC (normally open or normally closed ) that is rated for the service can be used as a priority relay.

A unit like reefer will use a wire when operating to the relay , to open the HW heater power line.

A simple switch can disconnect the relay operating wire when plugged into the power pole.

Used to be in the high priced Grainger catalog for about $60.US
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Old 07-28-2017, 05:19 AM   #15
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Quote:
Originally Posted by makobuilders View Post
[*]This can be ensured either through a timer on the waterheater, or perhaps a relay that triggers from a signal from the charge controller.[/LIST]
I've been chatting with Cristec technical support, using an example charger model that I had owned previously. This is the reply that I received:

"We may have a solution that could comply:
* using the existing battery temperature output to get the float information
* this would imply to adapt our sofware
Please see attached drawing."
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Old 07-28-2017, 08:15 PM   #16
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the opto coupler is always on, so you have to ground the RE0 input to have the output transistor go off.

An actual 12v dc relay would be easier to control and be more versatile (one with normally open as well as normally closed output contacts).
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Old 07-28-2017, 11:00 PM   #17
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Hmmm

I'm all for technology but...

Why not just have a breaker panel and pay attention?

Another "kinda" solution would be to get a good inverter and put it in "power share" mode.

On my inverter if I say set the shore power at 5 amps, and run the mictowave at 1000 amps, the inverter supplies the load and charges back the batteries later
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