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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Archive for the ‘12 volt’ Category


Solar for small cabin

Monday, June 22nd, 2009

Hi Jeff,

I recently purchased a small 600 square foot cabin that is wired for 12 volt dc. It has eight small florescent lights, a car radio and I also plug in a 19 inch 12 volt TV occasionally. In addition I purchased a used refrigerator Nova Kool model 3800 24volt DC for this cabin.

I am currently carrying two 6 volt golf cart batteries back and forth (for recharging) when I stay at the cabin on the weekends. I would like to make this process easier and am considering purchasing a Suntech 175W 24V Solar Panel, a charge controller, two more golf cart batteries and a power converter 24 volt DC to 12 volt DC. I plan to keep the lighting and power outlets at 12 volt DC and have 24 volt DC to power the fridge.

Am I on the right track? Do you know if Suntech solar panels are good quality or not? Can you recommend a charge controller and power converter for this application? Any other advice you might have for me?


Bob Kruckenberg


The solar module you are considering is a 24 volt module, and cannot be connected to a 12 volt battery system unless you purchase a $400+ MPPT solar charge controller that allows a higher voltage solar array to charge a lower voltage battery. If you use a standard charge controller, it will force the solar module to operate at half its normal voltage which cut its watts output in half.

Although I do not buy or install any solar hardware made in China for more reasons than I can discuss here, I will say that SunTech is one of the oldest and best respected solar manufacturers in China, but I was not pleased with workmanship on the few that I have purchased.

If you stay with a 24 volt battery to match the 24 volt solar module, you will need four (4) golf cart batteries, and I think you will find the lower cost voltage converters to be very light-duty for this application. We have had several fail when loaded near their advertised ratings.

Since this is a small cabin, I would keep the batteries and all wiring 12 volts DC as you can find almost anything in an RV or boating supply store that will operate on 12 volts DC. You cannot find much of anything to run directly from 24 volts DC unless you use the voltage converter, but then if it fails you lose everything.

Good Luck and buy a good LED flashlight!

Jeff Yago


Battery charging from a generator

Wednesday, June 17th, 2009


I have a 7500 Watt generator working fairly well except that the DC output to charge the 12 volt battery is ony 8 volts DC due to a problem I am unable to repair.

Will the 8 volt DC to the battery cause any harm to the 12 volt battery? I have been using a portable 12 volt charger to to keep the battery up to par.


Bob Libbon


You should never run a large generator like this just to use the battery charger circuit. Some generators offer this small DC charging power to trickle charge a battery while you are running the generator to power other loads, but you would use up a tank of gas just to charge a small battery like this.

You want to buy a high quality 120 VAC battery charger and plug it into the AC outlet of the generator. Select a charger that lets you select different amp charging rates to match the battery. You could easily power a large capacity charger with this size generator, so the charging process would be much faster and will save fuel.

One caution – cheap battery chargers will not work from most generators as they require the higher peak-to-peak voltage of a generator output, and if the generator voltage drops while under load the charger will stop charging. Be sure the charger specs indicate it can be powered from a generator.

If you have a half-full basketball with 30 PSI pressure inside, you will never add more air to fill it up if your air pump only goes to 20 PSI, even if you ran the pump all day. You cannot charge a 12 volt battery with 8 volts. Regardless of charger type – solar, generator, wind, grid, the charger voltage must be higher than the battery voltage. A 12 volt battery will require a charger that puts out 13 to 14 volts. At 12 volts the battery will be almost discharged.

Good luck,

Jeff Yago


Questions about small solar installation

Wednesday, April 29th, 2009

Hello Jeff,

Thanks for all the great information you provide BHM readers. I’m planning to install a small PV system using the instructions in your article in issue #116. This will be a very small system and used primarily for back-up during a black out. I have a Uni-Solar US-32 panel and Sunsaver 10 amp controller. I’m installing the panel on a carport roof, (I live in Massachusetts), running the wires to connect to one or two 12-volt deep-cycle marine batteries in my attached garage. I’ll be using the 2-pole fused disconnect and correct wire size for the panel and ground wires you recommend.

I have three questions.

1. What can I use as a bracket to mount the panel to the roof? I’ve seen small RV racks for sale and wondered if there is an alternative mounting bracket that can be purchased at a hardware store.

2. The wiring diagram in your article shows the load wires going to two 12 volt lights, hooked-up in parallel. I plan on wiring one light for the garage and continuing the wires about 30 feet to be run to the inside of the house. Those wires will be hooked up to a wall plate with a 12-volt cigarette plug receptacle mounted on the wall. I want to use the plug for a 12-volt TV or any other 12-volt appliance/charger that works using the auto style plug. What do you think of this arrangement and do you have any suggestions or recommendations.

3. Do I need to vent the batteries outside if they are in an un-insulated garage? I plan on putting the batteries in an insulated box for the winter and wondered if I can drill a hole into the top of the box and let the batteries vent into the garage.

Thanks for the help.

Ernie Smith


I can give you some general answers, but since we would not know everything about a specific installation, we cannot be too specific.

Although most solar dealers offer an “approved” angle “foot” to attach any solar module to a roof, I have taken 1-1/2 X 1-1/2 aluminum angle and installed the leg standing up to the side of the solar module and the flat leg bolted into the roof framing. Keep in mind that if you do not use the pre-drilled mounting holes on the back of the module you will void the warranty, so you might try a combination of two short lengths of angle back to back to make a “Z” shape. This will give you a way to utilize the bolt holes on the back of the module.

As long as your loads are 12 volt DC and wired in parallel, they do not all need to be at the same location. However, I would increase the wire size to the more distant load as there is 10 times the voltage drop at 12 volts DC that there is at 120 volts AC.

Finally, a few RV or golf cart batteries out in a garage will not give off enough gas to cause a problem due to the large space, but don’t locate them next to a gas fired hot water heater. Hydrogen gas is only explosive when highly concentrated like in a small sealed up closet or battery box. If you do place the batteries in an insulated box, you will need a vent at the top. For larger battery systems we use a 1-1/2″ PVC pipe vented outside, with screening to prevent insects from entering. The pipe needs to slope uphill since gas rises, but you will need something to keep out the rain.

Good luck,

Jeff Yago


Wiring batteries

Tuesday, April 28th, 2009

Hi Jeff,

I wanted to thank you ahead of time for you assistance.

We are going to have an off grid solar panel system. Is it possible to wire two 6- volt batteries together both parallel and series to get double the voltage and double the amperage? If not, what are your recommendations?

Thank you so much,

Jenelle Sherstad


You can wire two 6-volt batteries in series to make 12-volts. You can also wire two 6-volt batteries in parallel to double the amp-hours. But if you wire the same two 6-volt batteries both ways, you will get a lovely cloud of smoke from burning plastic insulation, lots of fire, and chunks of burning copper wire flying through the air. This is because you will be making a dead short from the positive to negative terminals on both batteries.

Either use four batteries, with each pair wired in series, and then the 2 pairs wired in parallel, or buy a really good fire extinguisher.

Good luck,

Jeff Yago


Charge Controllers for Battery Banks

Friday, April 3rd, 2009


I need to use 2 to 4 12VDC batteries in parallel to achieve the necessary amp-hours required for a project.

Will a Morningstar charge controller (Sun Light 10 or Sun Saver 10, for instance) reliably monitor the voltage and charging current of the battery bank as well as it does for a single battery?


Richard Heiser
Sacramento, CA


A solar charger is sized based on the following –

First, total short circuit amp rating of solar array X 125% .    Note- Under extreme cold and sunny days, its possible for a solar array to reach 156% of short circuit amp rating for short periods and this is used to size solar array wiring.  If your charge controller does not have this temporary surge capacity, you should use the larger multiplier .

This calculation will determine the “amp” rating of the charge controller.

Next, select voltage for charge controller.  This will be total voltage for battery bank.  For example, two batteries of 12 volts in series would require a 24 volt controller.  Four batteries of 12 volts in parallel would require a 12 volt controller.  Four batteries of 12 volts with 2 in series and 2 in parallel would require a 24 volt controller.

The controller doesn’t know or care how many batteries you have or how they are wired, as long as the controller design voltage matches the voltage of the battery bank.

Now that you know amp rating and voltage for controller, select a model with the options you need, like digital meter, low voltage dis-connect, and/or temperature sensor.

Good luck,

Jeff Yago


Battery and wiring questions

Saturday, February 21st, 2009


Would these batteries work as a battery bank — Caterpillar  175-4370-pho  Cat lists these as heavy duty, deep cycle, deep discharge they are 12 vdc.  I can get a good price on these from the cat dealer and they weigh 62#

On using a array of PV panels, for aesthetic reasons, would like to mount in back of house. This would mean a cable run of approximately 50 feet.

For a 12vdc system what size cable should I expect to use?  Same question but for 24vdc? I have access to some free cable if right size. Also is it normally multi strand or single solid conductor.

Cable from battery to inverter, approximately  5 feet  run. Expected cable size?

In choosing a inverter, if I use a 12vdc supply source (pv)  would the inverter have to be  12vdc input or is there one that is selectable input voltage? I expect to increase the incoming voltage as I can afford 2 or 3 more panels.

This unit will not be grid tied. It will be used for my shop, Expected maximum power usage at any one time, 1000 watts, then would drop off. I can only operate one tool at a time.

Biggest load to be expected for short bursts (3-5 minutes) 115 vac wire feed (currently grid connected) other loads is just small hand tools, circular saw, drill, saber saw , one flourescent light etc.




The 12 volt Caterpiller battery you referenced weighs 62 pounds.  A 6-volt golf cart battery weighs 63 pounds.  Since you would need two 6-volt batteries to provide 12 volts, this means a 12 volt battery made from golf cart batteries would weigh 126 pounds, or double the weight of the 12 volt Caterpiller battery you referenced.  The heavy weight indicates more lead plates which provides more amp-hour charge capacity.  If your system will not cycle every day from full to low charge, then this battery might give you good life.  However, most starter batteries are designed to provide one heavy discharge during starting, then several hours of slow recharge.  Solar systems do not operate this way.

As noted in many past answers to email questions, we cannot provide specific design answers like what wire size to use as there are many variables we would not know about your specific application, and we do not have the time for this level of help.  Please check the most recent article I have in Backwoods Home Magazine that describes how to make an off-grid solar system for a remote cabin which will answer many of your other questions.

Good luck,

Jeff Yago


Charging a 6 volt battery with a 12 volt solar panel

Sunday, February 1st, 2009

Hi Jeff,

I recently built a small alt-e project with my daughter.  It’s a shelf with a 6v van and a couple of led lites for over her bed.  It’s powered by a 6v 36 amp-hour battery in an ammo can under her bed.  I have a 4.5w, 300mA Coleman solar panel intended for trickle charging 12v batteries.  It charges at about 17v.

Am I right in thinking that with a system this small and with a current that low that I can use this panel with this battery without frying wire or battery, or should I hold out to find a panel that charges at 8v.

Steve Sonntag MD


In an emergency you could temporarily re-charge a 6 volt DC deep discharge battery with a 12 volt solar array, but I would not make this a permanent connection for the following reasons.  This Wal-mart solar charger was designed to trickle-charge a large 12 volt battery, and does not have a built in solar charge controller, which is available as an option from the manufacturer.  Supplying a higher voltage to a wet cell deep discharge battery is typical for periodic equalize charging, but it sounds like you have a sealed deep cycle battery.  If that is the case, over-charging from a high charging voltage will dry out a sealed battery and these cannot be restored.

Also, without a solar charge controller between the battery and the solar module, you have nothing to prevent battery charge from discharging back through the solar module, although this small solar module may contain a blocking diode to protect from this.  You may be able to remove the backing from this solar module and “split” the string into two groups of 6 volts, since many solar modules are made up from separate strings of individual cells like Christmas string lights.  Find the wiring point between two equal sets of cells and cut this wire, then tie the positive side to the positive output wire, and tie the negative side of the cut to the negative output wire.  Now you will have a 6 volt nominal solar module.  Keep in mind that many commercial 12 volt and 24 volt modules have internal junction boxes set up to allow you to do this with these larger units.

If all else fails, buy a 12 volt battery, fan, and light.  They are probably easier to find than 6 volt units anyway.

Good luck,

Jeff Yago


Battery hookup

Wednesday, December 24th, 2008

I hope this is a easy question.

I have a motor home that has 3 deep cycle 12 volt batteries.

I want to keep them charged with solar as much as possible.

Will connecting 2 or more 45 watt separate systems charge them better than just one?

As they are all the same watt I am not sure adding 2 or more same watt systems will charge any more than 1.

Help Please.

Thank you

Att: Help Please:

I assume you mean connecting each battery to its own solar module and charger verses connecting one solar charging system to all three batteries. For good battery voltage balance, its better if you connect one solar charger to all batteries wired in parallel. I don’t know how you could do this separately unless each battery can be disconnected from the others, since normally they all are wired to the same 12 volt positive and negative mains. Assuming you could separate them from each other, as soon as you connected a battery that was at a higher charge than the others, current will flow from one to the other until they are equal in voltage.

Keep it simple,

Jeff Yago



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