Load Diversion in a system with 2 Midnite Kid MPPTs...

Boatman · September 2016

Got a couple of questions about load diversion. I'm building a PV system for a cruising catamaran. The normal loads will be relatively light and all 12 volt – no inverter. Loads will be a small refrigerator, interior lighting, navigation and communication electronics, personal electronics charging, and infrequently an autopilot. Based on advice I received in reply to a previous post from some helpful folks here, I have assembled a system. It looks like this:

2 Panasonic 325 Watt, 96 cell panels, each controlled by a Midnite Kid charging 4 @ 31 series AGM batteries. My goal was to have both significant excess charging capacity and system redundancy in the event of a component failure. I decided to go with much more capacity than I will likely need. I hoped this would compensate for multiple cloudy days and allow me to use a 12 Volt water heater as a diversion load.

Heating water on a boat, if you don't have an inboard motor with a heat exchanger is a major PITA. My cruising catamaran has 2 outboards which cannot be used for that purpose. My boat has a propane stove, but there are no propane water heaters I have found that are ABYC certified. I confirmed this with several marine surveyors. Folks can run into problems if they ever have a propane related incident on their boat. Insurance companies usually will not cover damage caused by a non-ABYC certified device.

I'm trying to figure how to use the LOAD DIVERSION feature on the Kid to divert exell charge capacity to a water heater after the battery bank is at float. The instructions on the Kid say that for two controllers, they do not need to be sync'ed, and can both charge the bank of 4 batteries independently. However, the instructions also say that only the Master Kid can be used for load diversion, which implies that only excess charge from one panel can be diverted.

This doesn't make sense to me. If both can operate independently, can't both divert load to the same source?

Does anyone know how to do this?

I'd appreciate any guidance.

Thanks...Boatman.

BB. · September 2016

If you do not get an answer here, Midnite has their own forum where you should get an answer pretty quickly:

http://www.midniteforum.com/index.php

-Bill

Dave Angelini · September 2016

You do not have enough solar to even dream about heating water electrically, and certainly not reliably. Are there females?
It is so easy to heat water directly with the sun on a boat. Look into it! I have been there!

jonr · September 2016

Say you can get by on 5 gallons of water heated up by 40F. About 500 watt hours or both of your panels for one hour.

I used to light the water heater, shower and then turn off the gas valve (in the line before the heater). I'm sure it wasn't ABYC certified, but I also think that it was very unlikely to cause a problem (because it wasn't connected 99.9% of the time).

Boatman · September 2016

Dave: Not sure I understand why I can't even consider a 12V water heater. I have 2 @ 325 watt panels. The only significant load I have a 4 cu ft refrigerator with a danfoss compressor. All other loads are fractions of an amp other than the autopilot, which I seldom use. The 12 V water heater I'm looking at is 5 gal and only 300 watts (about 25 amps). My wife and I are experienced cruisers and know hoe to take quick showers with little water usage. We can get 2 showers out of 5 gals. It seems to me that with 650 watts on hand, I ought to have lots of spare charge capacity.

All: The original question was whether I could use the LOAD DIVERSION feature of BOTH Midnite Kids to divert all charge to a 12 V water heater once my battery bank was at float. I posted this question to Midnite tech support and got a confusing answer. Follow-up question has yet to be answered.

Thanks...Boatman

Dave Angelini · September 2016

You can do whatever you want. My input is if you ever have been cruising you would know that running electric refrigeration on a boat is tricky enough as you really can't carry enough square footage of solar to run all the things that are there. Then you add a huge load that is coming on at the same time the refrigeration needs to run. Go ahead and try it.

BTW you really do not have 650 watts to use from 650 watts of solar panels!

I just want to add that I have seen a few of these water heating schemes go bad because of the way they are wired. It is a very bad thing to have electrical problems and maybe a fire offgrid where my business and life is centered.
It is much worse for this to happen on a boat at sea!

A small 5 watt hot water pump circulating into a 12" square homemade solar hot water collector will easily get you 140F water in a 5 gallon tank in 3 hours of sun. To me it is a no brainer to stay away from electric hot water on a boat.

You are suppose to be making your life simple when you cruise, at least that was the way I learned.....

jonr · September 2016

3 hours of sun on 1 sq foot might yield ~450 btu. 5 gallons raised 40F (eg, 70F to 110F, well short of 140F) needs ~1700 btu (ie, not even close no matter what efficiency you pick). A 2'x2' panel would be better.

I don't know anything about the Kid or understand your battery wiring - maybe you could wire the load diversion output to a relay that would turn on the water heater (running from the batteries).

Dave Angelini · September 2016

I know it worked because I did it and did not use math! Have you Jon?
Ok I guess I did some math, but your math is leaving out variables. Two of them are the ambiant air and sea temperature.

Back then we did not have or know of a water heater that ran on 12vdc? Pretty rediculous even now....
They were diesil engine heated or direct solar.

Boatman · October 2016

Dave:

That's a really interesting idea. Hadn't thought of heating the water directly. Seems like it would be efficient but I'd have to pay close attention to insulating the lines that carry the circulating water.

Do you have any pictures of what you did?

Thanks for your help...Boatman.

Boatman · October 2016

Found the Heliatos EZ-37 2' x 2' solar hot water panel on line for $137 with free shipping. It's very light - like 12 pounds. Sounds like a deal. I'm thinking I could use the 6 gal. hot water heater I planned to convert to 12V and use it as a hot water storage tank for a solar hot water circulating system. I'd just have to run a thermostat of some sort in the solar water panel to turn on the circulating pump when the water in the panel got hot.

Anyone have any experience with the Heliatos hot water panels? Quality? Durability?

Thanks...Boatman.

westbranch · October 2016

a couple of links, the Laing page has a nice pic of the hook up
https://www.ussolarpumps.com/product/d5-solar-hot-water-pump/

http://shop.solardirect.com/product_info.php?products_id=880

and there are 3 models of laing http://www.houseneeds.com/solar-heating-solar-fans-solar/solar-hydronic-heating/laing-pump-dc-solar-vario-strong

can be hooked direct tot a PV ~ 25 W max

Dave Angelini · October 2016

Boatman I do have some pix of what we did on Astraea but they are photos and movies that I did digitize but have not spent the time to make them easily acessable. circa 1992. stop by there 18 hours of video.....

We only cruised in warm or hot air/water so insulation was more to protect someone from being burned. We used an El Cid hot water pump that ran off a 10 watt small solar panel. It can run off 12vdc also just pick the right pump. Google them, they are in Jupiter Florida.
We used a 140F snapswitch (Solar hot water luanguage) which is a thermistor that when close to 140 opens up the power to the pump.

I built a small collector out of an old aluminum amplfier chassis and used 3/8" copper tubing (coiled with heat sinks from lots of transistors) and Lexan for the business end. Installed in a place close to the hot water tank as possible. 40 feet would be fine if you double the size of the collector. We both showered every other day and snorkeled the odd days.

Install a overpressure valve to protect the crew and you are done. It lasted the whole 10 years. We had a 7 gallon water heater failure about 1/2 thru and I believe that was caused by the diesil engine heating loop into the water heater. On the next heater I placed a valve to just turn it off for long motoring runs.

Either too much wind or not enough 80% of the time, carry lots of diesil... good luck!

The El Cid is an amazing pump. I first found them when trying to find a 10 watt phantom load on a Boat I was outfitting. It was being used as a refrigeration saltwater cooling loop. It had been disconnected (not really) and was just running dry 24/7 for 2 years. No seals or shafts just a very nice bullet proof pump.

Boatman · October 2016

Dave. Checked out the El SID pump. Looks like a great design - all stainless and teflon, about 0.9 amp draw, no seals or shafts. Looks like a great product. However it only has a head rating of a little over 2 feet. Since my panel will be on the cabin roof, it will have to be about 6.5' above the tank. Once the system is full of water and all air is purged, there technically will be no head, but I'm not clear how to get air out of the system and keep it out under normal operation. I've found some automatic air vents used in rooftop solar systems, but not sure how well they'd work in this application.

How did you overcome this issue in your system?

Thanks for your patience and guidance. You've already saved me lots of time and headaches.

Boatman.

Boatman · October 2016

Dave: You know, it just occurred to me that I could take the Force 10 water heater I had planned to use as an accumulator tank and use the heat exchanger coils in it to make a closed loop solar hot water heater using glycol in the panel. Then I would only have to purge the heating loop once and keep it closed.

Not sure if this approach would add another complication or make operation easier over the long run.

Would appreciate your thoughts or anyone who has tried this approach.

Thanks...Boatman

Dave Angelini · October 2016

The key to either of your questions is the use of valves rated for 250F water.
In the first, you need valves that is in a tee loop to vent the water out into a small water pail. One on each so you can drain the sysem.
In the second, you can use valves to select either the engine loop or the solar loop.

When we were out there was another boat that had an electronics background and he told me cruising has ruined you for corporate life. He said to get into Offgrid Solar, nobody knows what they are doing in that business... If you meet anyone who wants to go offgrid please send them my way. Good Luck

BTW the easy way to make solar hot water on a home type water heater is to buy one with what they call a hydronic loop. There are many who use a home water heater for radiant heating and domestic hot water and these are perfect. They are essentially the same as what you have on a typical marine water heater.

Boatman · October 2016

Dave:

With an open loop system that includes a traditional water heater as a storage tank, there already is a drain spigot on the bottom of the tank, which would be the lowest point in the system and work well as a drain to get the water out of the system prior to a freeze (can get pretty cold in Annapolis in the winters).

Actually, I was just thinking of going closed loop instead of open loop. I have twin engines on my cat, but they are outboards, not inboards. Since they are raw water cooled, there is no way for me to use a standard heat exchanger for water heating. What I was thinking is that instead of looping my heating water through a cabin top solar water heating panel, I could run glycol though the panel and through the heat exchanger coils in my Force 10 water heater and use the circulated coolant from the panel in place of typical engine coolant heated heat exchanger.

Just figured it would be easier to keep a closed loop system air-free than an open loop system like circulating potable water through the panel.

Once I get the boat set up and working, I'll turn my attention to my two houses...If I have the time and inclination. Now that I've retired, sailing and fishing often interrupt my projects.

Thanks...Boatman

Dave Angelini · October 2016

You must be closed loop back there. Good Luck!

Load Diversion in a system with 2 Midnite Kid MPPTs...

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