Energy draw switch

8 Posts
Jun 7, 2011 07:52 pm
Energy draw switch

I own a small island in Canada that isn't connected to the grid. About 3 years ago we got our first renewable power, a simple 15 W panel and 4, 6v 450Ah deep cell batteries wired for 12v. (We only spend about a week every year at the island).
However, a friend of mine's company has 400 leftover deep cell 12v 100Ah batteries and is giving my friend as many as he wants for free to save money on disposal fees.
My friend told me I could have as many as I want from him, so I would like to add 12 to my bank of 4 for a total of a 16 battery, 2,100Ah 12v bank.
Having a much larger bank, I will be buying more solar panels and hopefully a wind turbine.

I'm looking for some sort of control box that will allow my house to draw power directly from the panels and wind turbine, but if the house overdraws it would then pair with the battery bank to supply the house with what it needs. In turn when the house is drawing less power or no power, the panels and wind turbine would charge the bank. This would be in effort to make the batteries have as long a life as possible.

2 questions.

1 does this box exist and what is it called?

2 would it be more efficient for me to just simply wire everything to the battery bank?
462 Posts
Jun 10, 2011 08:03 pm
Re: Energy draw switch

Steven, what you are looking for is a charge controller. You can find many here at Alt E. store. But first you have to determine how much power you plan on producing. eg. How many watts from all the panels you plan to buy. Right now you only have one 15 Watt, 12 volt panel so you only produce around one amp. Charge controllers go by amps so a small morningstar controller would work.
 It is usually not a good idea to mix batteries so you may need to have a couple set ups, one with the six volt batteries and one with how many of the new 12 v batteries you plan on purchasing.
 I would skip the turbine since you are only at the house one week a year. This is plenty of time to charge the batteries using your PV. Just do some math. Right now, that one 15 Watt panel would take around 1000 hrs of sun to charge the four 6 volt batteries to capacity at 12 volts. At 6 hrs of sun a day, that would be around 170 days.
 You can use the calculators here to determine how much power, or how many of a certain panel you need depending on how many of the new batteries you decide to use. Also figure out how much power you actually need or use each time you are on the island. Then you can figure how much power needs to be replaced.
8 Posts
Jun 10, 2011 11:21 pm
Re: Energy draw switch

Thanks for your reply. I am new to energy systems like this, but I'm learning.

The reason I wanted to add a turbine is because we have no way of warming the batteries over the winter and it is just too much for us to transport them every year. This means that the batteries are subject to -40 degrees F with several feet of snow and at most 2 hours of sunlight a day. 2 years ago I arrived to find all 4 batteries had frozen and blown there cases. We remove all loads from the batteries in the winter which means the batteries wernt charged fast enough to keep up with what they where losing to the cold.

Could you also point me in the right direction on how I could keep the 12 and 6 volt battery banks separated while both being connected to our 1200 W inverter?

And, as long as the 12v batteries are in series, and the 6v batteries are in series/parallel (making 12v)... is there really a problem with connecting them together?

Thanks in advance for replies!
99 Posts
Jun 11, 2011 05:44 am
Re: Energy draw switch

I would recommend wiring the batteries at 24V instead of 12V for a variety of reasons (you can Google for plenty of explanations about benefits/drawbacks of battery bank voltage).  You can do that by putting 2 12V batteries in series or 4 6V batteries in series, and paralleling them.  You will definitely want a charge controller to apply the appropriate charge to the batteries.

I don't think mixing different kinds of batteries in parallel at the same voltage is so terrible an idea as is commonly believed.  It may be that the weakest ones are cycled the most and need replacing before the other ones, but they'll be better off and longer lived than if used on their own without being paralleled with stronger batteries.

As far as managing how the loads draw power... just wire all of your loads to the batteries.  If your solar/wind are producing, the loads will essentially skip over the batteries as if they're just a wire, and draw from the output of your charge controller.  If your charge controller isn't putting out enough, the loads will draw down the batteries to make up the difference.  There isn't any special logical device required to do this, it's just how electricity behaves.

Regarding freezing protection for your batteries, I would recommend putting them in a very well insulated enclosure and installing a thermostat-controlled heat source inside such as heat tape (connected to a heat sink for safety) or a lightbulb.  My Pennsylvania winters don't get as cold as yours, but we do have long nights which reach below zero Fahrenheit. I have my batteries in a very well insulated shed and I have a 100W-eq compact fluorscent lightbulb which turns on when the temp gets below 34F.  Because it's well-insulated in there, this is sufficient to keep the temperature from getting much below freezing.  I think the actual draw of the lightbulb is around 25W, so even if it stays on 24 hours, it's only 600 watt-hours per day.  If you had only two hours of sunlight, two 150W solar panels tilted toward the southern horizon could supply that amount of power.  It seems counterintuitive to save your batteries by drawing them down with a load, but in this case, the load draws less than the cold would.

BTW, I also think a wind turbine is a good idea, and a 1kW model would provide plenty of power to keep your batteries warm if coupled with a small heat source as described above.  It shouldn't cost more than about $10k installed.  I own a Bergey XL.1, and it works great.
8 Posts
Jun 11, 2011 01:27 pm
Re: Energy draw switch

I have looked at the advantages of a 24v system, however, because the batteries are very close to each other and the inverter, and i don't run DC straight to the cabin, I don't think it would have much loss across wires, and I would rather deal with the small loss from the inverter, rather than buy a whole new one to support 24VDC. Maybe there is a much larger advantage that I'm not seeing?

With regards to what I would get with a wind turbine, I am only at the cabin 1 week out of the year, and would prefer not to spend 10k on my system. There is regular thievery where my island is because everyone is gone for the winter, and i fear if i had a more expensive system, it would be gone when i arrived the next year.

I do like your idea of insulation and a heat source, I've actually thought of it in the past, though, I would have to find the most efficient low heat source possible, as i really only plan on ever having 180 watts worth of panels and less than 500 watts in wind power.

The only things that require power at our cabin is an on-demand DC water pump, 14 45Watt eq florescent bulbs, 3 cell phones and 2 laptops. (Both our fridge and stove run off propane)
In the future i would like to add a few more things like a ceiling fan, but don't really require anything else. The only reason I'm adding batteries is because there free.

Thanks again for the reply.
« Last Edit: Jun 11, 2011 01:28 pm by Steven Messer »
462 Posts
Jun 12, 2011 10:14 am
Re: Energy draw switch

Steve, if you keep the two battery banks separate, each with their own charge controller, there should be no problem wiring leads from each bank directly to the inverter. The main reason to keep them separate is so they charge correctly and to capacity. One bad battery can ruin the bank's ability to charge correctly. Also having two set ups adds redundancy to the mix. If one system fails, at least the other is still up and running. A good thing if you are only there one week a year to check on things.
  Building an insulated box as Thomas A. suggests is also a good idea. Just make sure it is vented to allow gases from the batteries to escape. Using a thermo-electric heater along with a cheap thermostat could work for you. You can buy a cheap thermo-electric cooler and rob the unit from it. Or use the cooler itself as the insulated box if it is big enough, or modify it.
 Just curious, where are the batteries located now? Just wondering why they are freezing.
8 Posts
Jun 12, 2011 10:38 am
Re: Energy draw switch

The Island is located along the boarder of Minnesota and Canada, on the Canadian side. I live in Wisconsin, so its too much of a hassle to haul the batteries too and from there every year.

My question with connecting both banks to the same leads of the inverter, isn't that the same as them being all connected together anyway? Since if one bank has less charge, the other bank would still be directly connected to it, and electricity would flow accordingly.
462 Posts
Jun 12, 2011 10:54 am
Re: Energy draw switch

...guess you misunderstood.Again, "if you keep the two battery banks separate, each with their own charge controller, there should be no problem wiring leads from each bank directly to the inverter"
 So Yes, you can hook up leads from both banks to the inverter. It is the charging situation that should be considered when mixing different types of batteries.
 Just think of a pool of water, if I have one hose dripping water into the pool and another with a steady stream, the flow coming out of the drain cannot determine, or doesn't matter or care which hose is flowing faster. But if I try to hook up the steady stream hose into the supply of the dripping hose, I will only get drips coming out of the drain.
 As far as location of the batteries, I meant the physical location of the batteries, eg outside shed or porch, not the geographical location.
« Last Edit: Jun 12, 2011 11:00 am by Tom Mayrand »
8 Posts
Jun 12, 2011 11:08 am
Re: Energy draw switch

There in the open on the floor of an un-insulated dock house built 30 years ago. The same shed where gas is kept. (I didn't design the system). However, this year I plan on building a separate, insulated, box on the outside wall of the shed.
99 Posts
Jun 12, 2011 02:58 pm
Re: Energy draw switch

Wow that sounds really unsafe.

I agree and should have mentioned the need for ventilation. But that doesn't mean it needs to be exposed to the elements.  Hydrogen is the lightest element, so as long as it has a path to escape at the top, you can keep the enclosure otherwise pretty tight.  I have a 1.5" PVC pipe from the top of my boxes leading out my shed roof.

Another consideration, if you're building your box on the outside of your shed, is to put it on the south side so that it can collect some solar heat during the day.  And if it gets snowed in, that's actually not a bad thing, because batteries are fine at 32F as long as they have a charge, and snow is a great insulator.

I disagree with Tom Mayrand about the need to keep the banks separate and I agree with your intuition.  If they are connected with sufficiently sized cables (triple aught for 24V), whichever bank needs more charge will get it, like two pools connected by a canal rather than a garden hose.  However, there are limitations based on system voltage.  At 12V, I'm not sure you could get cables thick enough to make it work.  You need to determine the maximum amps you expect (and I would leave room for system expansion later -- it usually happens) and calculate the size of cables you need.

Here's some more info on 12V vs 24V:
462 Posts
Jun 12, 2011 05:55 pm
Re: Energy draw switch

Thomas A. We are not sure what type of batteries Steven is using. If one is gel and another is sealed or lead acid, mixing the two types could create a problem. This is another reason why I suggested keeping the two separate. Remember, charge controllers usually have a switch for different types of batteries. Redundancy, as I mentioned is also a good consideration. Safety first. Especially if the owner is not around to check on things. An ounce of prevention is worth a ton of fire and a ruined vacation home......
8 Posts
Jun 12, 2011 06:01 pm
Re: Energy draw switch

The batteries that are up there are 6v 450Ah deep cell Maintenance flooded lead acid golf cart batteries. The new batteries are 12v 100Ah deep cell sealed Maintenance Free lead acid batteries made by CATerpillar.
I also have a pretty much unlimited amount of copper battery cable.

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