Top Navigation  
U.S. Flag waving
Office Hours Momday - Friday  8 am - 5 pm Pacific 1-800-835-2418
Facebook   YouTube   Twitter
 Home Page
 Current Issue
 Article Index
 Author Index
 Previous Issues

 Kindle Subscriptions
 Kindle Publications
 Back Issues
 Discount Books
 All Specials
 Classified Ad

 Web Site Ads
 Magazine Ads

 BHM Forum
 Contact Us/
 Change of Address

Forum / Chat
 Forum/Chat Info
 Lost Password
 Write For BHM

Link to BHM

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

Wondering about a great new energy-saving device
you found on the Internet? Then CLICK HERE!

Sorry. Jeff no longer answers questions online.
This will remain as a searchable
resource for all BHM website visitors.

Archive for the ‘Charge Controller’ Category


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


Lithium-ion batteries for solar lighting

Wednesday, March 11th, 2009

Dear Jeff,

Thank you for writing such an informative article on outdoor solar powered lighting, I do however have a few questions which i would greatly appreciate answers to.

The first of which is to do with the type of battery used in such a system. Is it possible to use a lithium-ion power battery to charge a system similar to that you have described. If no, why not and if yes, what should I look out for.

My second question is to do with the charge controller, in figure 7 you have a picture of a Sunlight-10 charge controller (the one on the right).  Can this devise be used in conjunction with a lithium-ion battery or does this devise only work with more conventional lead acid batteries. If so can you recommend another type of charge controller with similar features to the Sunlight-10 that can be used with a lithium ion battery?

Thank very much for your time and I look forward to reading your response.

Kindest regards

Kane Miller


The main reason lithium-ion batteries are not used much for solar is they are not making them large enough yet and the cost of what they do have is so far out of sight that it does not make sense.  Any short-comings with AGM or Gel batteries are easily made up by their much lower cost.  Sharp is working on a 18 Kwh lithium-ion for solar home power but these are thousands of dollars right now.

I suggest that you don’t make this any harder than it has to be right now,

Good Luck,

Jeff Yago


Voltage regulator vs charge controller

Thursday, January 22nd, 2009

Hi Jeff,

I’m building a wind generator using an automotive alternator. The alternator has a voltage regulator in it. Do I still have to use a charge controller in my system? What, if anything, is the difference between a voltage regulator and a charge controller?



Automotive type voltage regulators are designed to regulate the battery charging current by varying the voltage to the coil winding of the alternator, with a limit of 14.5 volts. In other words, the voltage regulator in an alternator operates like a variable speed control with a constantly changing charging current based on battery voltage.

A solar/wind charge controller has three specific charging levels that change based on battery voltage and sometimes also based on time. To reduce charge time, the charge controller first goes into “bulk” charge mode which puts the maximum charging current into the battery bank. This usually lasts about 2 hours and can be programmed, unlike the alternator which has no programmable setpoints.

This really speeds up battery charging due to the high charging current. After about 2 hours, or when a programmed voltage setpoint is reached, the charge controller switches to “absorption” charging, which is a lower charging current which slowly tapers down as the battery nears the full charge setpoint which can be programmed based on the battery size and type.

Once this final setpoint voltage is reached, the charge controller switches to “float” mode which is a small constant charging current at a programmed level just to keep the battery at a full charge level and offsets any standby losses for a battery at rest. In addition, the temperature of any battery has a major impact on charging as the battery voltage which controls a chargers output is different at the different charge levels than a battery at standard temperature of 77 degrees.

Since an alternator has no temperature sensor, the alternator charging is base on the expected average temperatures a car or truck battery will be exposed to, and cannot maximize charging efficiency by adjusting the charging voltage based on battery temperature.

I think you will find the improved charging performance and shorter charging time makes a charge controller well worth the cost over any standard voltage regulator built into the back of an alternator.

Good Luck,

Jeff Yago


Adding wind power to solar system

Saturday, December 13th, 2008


Do you need any special equipment if you want to add a wind turbine to an existing photovoltaic system (other than the turbine and support system for it)?

Bill Hiltscher


Older model wind turbines required a charge controller to regulate the charging current going to the batteries and to provide a way to load up the turbine to reduce over-speed in high winds once the battery was charged and there was no load on the unit. The solar charge controller and wind charge controller can be used together and even charge at the same time as they do not allow for one charger “back-feeding” into the other one.

Some newer wind turbines include built-in electronics so you do not need a separate charge controller, and even newer models put out 120 VAC which can go straight back into the grid without charging any batteries.

Hope this helps,

Jeff Yago


Adding a secondary generator

Wednesday, November 26th, 2008


My question is about this article: Add solar power to your truck camper

The article is great for getting started with solar/battery systems. I never knew it was so simple.

My question is, how would one add a secondary generator for days when the batteries are dead at night? Basically, I want something that will combine the power of the solar, with the power supplied by the alternator in my car. That way each power source can charge the batteries.


Anthony Hildoer

Any boating supply store will have “dual” battery chargers, “dual” charge controllers, and “dual” voltage regulators. There are other solar suppliers you can check out, but for small 12 volt systems you can usually find these items at a local boating supply store. Almost all recreational boats have two identical batteries and a switch to allow changing from one to the other. This makes sure if you run down one battery while listening to radios or running lights while anchored out in the water, you will still have a fully charged battery to start the engine. The dual battery voltage regulators will charge the first battery then the second battery without connecting them to each other. That was the equipment used in the article.

On the other hand, if you wanted to also charge this battery from a separate energy source like a solar panel or small gas generator, just be sure to use the proper charge controller for each source which will allow charge to flow into the battery even if it is also being charged by other chargers at the same time. The charging current from the other charging sources will not “back up” into each other. As long as each charging source has its own charge controller, nothing will cause a problem with the other devices. However, if one of the charging sources has a much larger charge capacity or is set for a higher charging voltage than the others, it will take over all of the charging as the other charge controllers will “see” this higher voltage and assume the battery is fully charged and then stop their charging.

Good luck,

Jeff Yago


Build a charge controller

Saturday, October 4th, 2008

I have been looking into building my own wind generator from a treadmill motor and I have seen where others had built a homemade charge controller but they didn’t explain it in detail. Could you explain to me how to build a charge controller and wire everything up and maybe show some pics of this and I was wondering if a person could use an old car battery charger/jumper and convert it to a charge controller and if this will work how to do it




Sounds like you have lots of time on your hands, as a commercially made charge controller this small would most likely cost under $50. However, if you want to build your own, the link below will provide all kinds of free design information for this and other home-made solar power equipment.

Your biggest problem will be matching the RPM required by the generator to produce the right voltage and current, and the speed of the blades. You will also need to design some type of over-speed control or limiter since any wind turbine can over-speed and start slinging blades in all directions in a high wind if not protected.

Most charge controllers in cars are not designed for your needs since most control the output of a brush-less alternator which is AC, not a generator with brushes which is DC.

Here’s the the link:

Good luck,

Jeff Yago


Add solar module

Tuesday, August 5th, 2008

I have 2-80 watt & 2-120 watt modules 200 feet from C-40 controller. I am connecting them in series to get 86VDC to controller (max 125VDC). At the controller I want to add another module (175watt @ 43VOC). The system voltage is 24VDC.

What voltage can I expect at the controller?

Is this OK?




What can you expect from the controller – how about smoke?

The C-40 controller is not intended to be connected to a solar array that has a different voltage from the battery bank. The reason for the high 125 VDC nameplate limit on the input voltage for this controller is to protect the controller during no load and low temperature operation when any solar module will have an open circuit voltage that is much higher than its normal operating output voltage.

Think of it this way – this is a pulse-width design controller which means it is just acting as an on-off switch to turn on and off the flow of electricity from the solar array to the battery. Depending on how charged or dis-charged the battery is, the controller will cycle this switch to the “on” or “off” position for different lengths of time (pulse-width), but its just acting as a switch and does not “convert” the higher voltage from a solar array into a lower battery voltage. Putting this high voltage into the low voltage battery is not good and could either over-heat or dry out the battery bank.

You have two options:

1. Purchase a maximum Power Point Tracking (MPPT) solar charge controller which does adjust battery charging voltage and will allow connecting a higher voltage solar array to a lower voltage battery. It will check the voltage input of the mis-matched modules and adjust the output current and voltage to the correct levels.

2. Buy a second C-40 controller and put each solar module group on its on controller, connected to the same battery bank. They will work together.

Good luck, and buy a fire extinguisher.

Jeff Yago


Double duty for a Honda/Yamaha inverter generator

Wednesday, July 23rd, 2008


I have a remote cabin that I am currently running off of a Honda EU3000is generator. I am planning on adding a battery bank, inverter and solar panels at a later date as funds allow. In order to save money now, I was thinking that I could buy the battery bank and hook up the battery bank to the inverter on the EU3000. Why not use the EU3000 inverter for double duty? I could get 110V pure sine wave power off of the bank or the generator.

There would still be the issue on charging the battery bank (you would need to purchase an appropriate charger for the bank) – could you charge the batteries from the EU3000 and run the EU3000 to provide 110V power simultaneously. I would then add the proper pure sine wave inverter to handle the solar panels, charging the bank from the EU3000 and to provide 110V power.

Too complicated? Not any monetary savings? Crazy idea? How would you go about engineering the system so you didn’t hurt anyone or damage/destroy any electrical equipment?


Paul Chan


This is a standard layout for a generator based off-grid homes without solar. I would match this with a Xantrex 4024 or an Outback 3624 inverter if you plan to expand later, but these are a little large for your 3 kW generator, and you will need to adjust the battery charger setpoints or they will overload the generator. In addition, these inverters can be programmed to “assist” a generator which means during battery charging and also supplying other 120 volt loads from the generator, if the generator demand goes above setpoint, the inverter will first back off the charging to reduce the load.

If the load still is increasing (like starting a well pump for a few minutes) the inverter will take some battery power back and “assist” the generator to avoid over-loading. You can even program either of these inverters to start the generator when the battery charge level drops below a minimum setpoint.

For this type system, its best to operate your LARGEST loads while the generator is running and also charging the batteries, instead of first charging the batteries then stopping the generator and powering the same loads from the inverter. Since there is a loss of efficiency during the charging process and again during the inverter process, large loads are better operating only when the generator is running and supplying the power directly.

Since the solar array will have its own solar charge controller, this will be totally separate charging system, although it will be charging the same batteries so you can add the solar later. You can also add solar modules a few at a time since they are expensive, but get the charge controller that will be large enough from the start so you don’t have to keep upsizing.

Good Luck,

Jeff Yago



Copyright © 1998 - Present by Backwoods Home Magazine. All Rights Reserved.