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

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Archive for the ‘Charging’ Category


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


Charging 6 volt batteries in a series

Monday, June 15th, 2009


I have a 36 volt (6 6-volt batteries) Cushman golf cart.

Can I bypass the old charger and use a 6-12 volt battery charger to charge these six 6 volt batteries wired in a series? If so where do I put on the + and – cables? One on the first battery and one on the last battery in the series?

Thank you for your time



I am not sure why you want to do this but I am going to assume the on-board 36 v charger is dead, and you have this other charger around but it is a 72 volt charger (6 x 12)??.

My first suggestion is call or stop by a used golf cart outlet.  There is usually at least one in all larger cities having several golf courses.  They have tons of these used chargers around and will either give you one or sell you one very cheap since many people are paying to have these old carts re-furbished for use in RV parks and they usually include a new charger with each cart sold.  Be sure to get the right model as many of todays golf carts use six (6) batteries @ 8 volts each which require a 48 volt charger.

If your charger is really a 72 volt charger designed to charge six (6) batteries of 12 volts each, then you cannot use it.  It is possible to use a 12 volt charger and connect to two batteries at a time in series which makes 12 volts.  You would connect to the positive and negative of each set of 2 batteries, then move to the next set of 2 until all 3 sets are charged, or you could use a 6 volt charger (some 12 volt chargers have a 6 volt switch) and charge them one at a time the same way, but do not connect a higher voltage charger to a lower voltage battery set.

Good luck,

Jeff Yago


When to recharge a deep cycle battery

Sunday, May 24th, 2009


Thanks for answering my question about the battery charge at craft shows. I plan to buy the volt meter you suggested.

Is it better to let the deep cycle battery run down before charging it, or is it ok to charge it every day when using it daily, regardless of how much has been used?


Sam Allen


Your question is actually more complex than you probably thought since there are several different charging issues involved. If you read the fine print on any new deep-discharge battery, it will give its warranted life in a fixed number of total discharges. In other words, a battery with a 6 year warranty may only last 2 years if deeply discharged more times in the shorter period than warranted. This means a battery that is discharged 25% every day then recharged will normally last much longer than the same battery that gets discharged 75% one day each week. However, on the other side of this debate, a deeply discharged battery can take a huge charging rate which charges much faster if using a generator or solar array without out-gassing which will increase the need to add more distilled water more often.

The other re-charging issue relates to a large battery capacity matched to a small solar array. Typically what happens is the first day the battery starts out at 100% full, then is discharged 20%. The next day the solar brings it back to 90%. Again, the next day the battery is discharged another 20% so it now is at 70%, and the days solar adds another 10% leaving it to start the next day at 80%. This cycle continues until the battery keeps cycling in the 30 to 50% charged state and never gets fully recharged. This type situation will damage the battery because when the lead plates are never brought back to 100%, the surface area will soon develop a layer of calcium or other minerals which become insulators between the acid and the lead which reduces the plate area exposed to the acid and this means battery capacity is reduced. In many cases, this damage cannot be reversed.

The real answer to your question is based on how the battery is being re-charged. If you have a quality 3-stage battery charger that will “back-off” the charge rate as the battery reaches full charge to avoid gassing, then you should get the best battery life by shallower daily discharge and re-charge cycling regardless of battery capacity.

Hope this helps,

Jeff Yago


Checking a deep cycle battery

Sunday, May 17th, 2009


I have a deep cycle battery which we use with an inverter at craft shows to power the credit card machine and sometimes lights or fans. After using it all day and before going to the next show, I would like to be able to check the battery level.

How can I check the battery level?

I plan to get a second battery as a backup since we do multiple day shows and can’t afford to lose function of the credit card machine, but it would be good to know how much drain has occurred after a day’s use.

Thanks for your help.

Sam Allen


Knowing how much amp-hour charge is remaining in any deep cycle battery has been a problem still waiting for a solution, as there is no perfect meter that can tell you this. The only way to know the exact charge level of a lead-acid battery is to insert a calibrated hydrometer with temperature correction into each cell. Obviously that’s not going to happen, so you could take a voltage reading with a digital volt meter.

The problem is the volt meter will not give a true voltage reading while the battery is under load, as it will read too low, but it will also read too high when there is no load and the battery is at rest or was just charged. Many companies make a battery amp-hour meter that keeps track of how may amp-hours you put into the battery when charging, then will subtract from this total during discharge, but this also has to keep correcting itself due to temperature changes and how the “rate” of discharge can affect this reading and these meters cost several hundred dollars.

You did not say what inverter you are using, but many will include a battery volt meter which will give you a rough idea of battery charge.

Here is my suggestion. Buy a volt-meter from Radio Shack for about $15 that provides a digital display. Set for the lowest DC voltage range it has that can easily read in the 8 to15 volt range, but not more than 50 volts.

Add a “small” load to the battery. Nothing large and do not connect the inverter. Maybe a small 12 DC light or small DC fan you indicated you had, just enough to pull off the surface charge but not enough to start drawing down the voltage.

Note the voltage reading and compare with the following:

20 to 30% charged – – – – 11.60 volts

30 to 50% charged – – – – 11.90 volts

50 to 60% charged – – – – 12.20 volts

60 to 70% charged – – – 12.45 volts

80 to 90% charged – – – – 12.50 volts

Over 90% charged – – – 12.66 volts

The above chart is just a starting point for you. Once you take a few voltage readings and then see how long your equipment will run, you will be able to customize this chart for your specific battery. Please also note this chart is based on your battery being at 77 degrees F. If the actual battery temperature is higher or lower, this voltages will shift some, but not major until it is over 90 degrees or below 50 degrees.

Good Luck,

Jeff Yago


Inverter not charging battery bank

Sunday, May 10th, 2009


I have a Xantrex 2000 Charger/Inverter and 6 -12 volt, 250 amp hour batteries. I charge my Batteries from my generator and I am not connected to the Grid.

While the Inverter is charging, the volts read between 14 to 15 volts but go back down to 12 when the charging is complete. The Inverter only charges the Batteries to 12 volts and the Inverter shuts down at 10 volts, this leaves me with only 2 working volts.

How do I figure out if my Inverter/Charger is too small for my Battery Bank? Could I be missing an adjustment on the configure mode of my Inverter?




As I see it, you have 2 possible reasons for this problem. You indicate the charging voltage is around 14 to 15 volts during charging which would seem to be good, but you did not say what the charging current was. For example, your inverter could be producing the right voltage output, but little or no current flow which would mean the batteries are getting little or no real charging amps going into them. My first check would be the generator and checking the amp loading of the charger.

Many low cost generators have a voltage regulator that drops the peak to peak voltage of the output waveform when more loads are added to the generator as their way of controlling overloading. Although this method of load control does not affect lights and motor driven tools, most battery chargers and inverters in charging mode will stop charging completely. These chargers are designed to use the full 169 peak to peak volts (120 VAC is the average of this voltage) of the generator. In other words, battery chargers only use the “peaks” of the voltage waveform and if these peaks are cut off or reduced, there is a major drop in charging amps output.

My second guess is the batteries. If these batteries are either old in age, or are newer, but have experienced many extreme total discharge cycles, or go long periods with only a partial re-charge, then what you describe is a classic indication of a failing battery bank. Assuming you do have a good charging process, when a battery is in the condition I just described, it will get what we call a “skim charge” and shuts down the battery charging because the battery voltage goes up real fast which tells the charger to stop charging. However, the aging battery plates usually have very little lead remaining in contact with the acid as most of the plate area is covered with calcium buildup and no longer in contact with the acid. This in effect is like making your batteries much smaller, which causes the battery voltage to rise very fast under the heavy charging, yet little real charging is taking place. As soon as the charging process stops, the battery voltage will drop almost down to a totally discharged level of around 12 volts since it was never really re-charged, and will quickly drop even lower when a load is connected, which also is what you have described.

I would not only suggest replacing these batteries, but I would switch to a deep discharge type of battery like a 6 volt golf car battery or larger L-16 battery. This will give you more amp-hours of capacity with fewer batteries wired in series. Its always better to have only 1 or 2 battery strings in parallel, as one string will always end up getting most of the charge and most of the discharge when you have 3 or more strings in series.

Good luck,

Jeff Yago


Hydro generator system

Friday, March 6th, 2009

Hi Jeff:

I purchased DC-512 four alternators over the Internet for a hydro project. I’m taking advantage of an existing irrigation system on a farm, which pumps a steady stream of water with great pressure at a very long distance. It’s like a fire hose in action.

This system is running continuously for 12 hours daily. I’ve designed a special, very light aluminum=blades arrangement and I have adapted it to the DC-512 via belt drive to disrupt the powerful irrigation water stream, moving this blade as when cleaning a painting roll with a pressure hose. This creates a speed in the DC-512 of 1150 RPM as measured with a tachometer. The voltage produced with no load, e.g., disconnected from the batteries, is approximately 25 volts, measured with a Flux digital meter.

The DC-512 were all connected in parallel to a single 12 volts Flex-Charger of 100 amps to charge a battery bank, 4 batteries connected in parallel. Three alternators DC-512 were disconnected from the charger to perform troubleshooting leaving just one connected in parallel. This is what happens; when I connect the positive cable to close the circuit, seems like a short circuit is created in the alternator, which slows down the speed to about 500 RPM stopping the blades and disrupting its function to load the battery bank. The charger light turns on indicating that is charging but, producing only 13 volts, which is not really enough voltage to charge the batteries. I have connected everything precisely as per alternator and charger instructions. Finally, I am tired of getting wet like crazy during test and troubleshooting process. I wonder if you can explain what is happening and how can I make this system work. Your help will be really appreciated.

Thank you in advance.

Carlos Echevarria


As it states on the web site, we can not answer specific design questions as we do not know all of the specifics of your installations, and this is a free site and we have limited time to spend on each email question. However, we can provide general answers that may be of some help.

First, I assume this pressure flow is due to gravity head and not from a pressure pump somewhere. Second, if I had this much “free” water flow I would purchase a quality hydro-generator that is designed to maximize the conversion of energy. Most likely a properly sized and designed unit could replace all four of your home-made units and without all the problems you are having.

If things work fine with all four alternators in the circuit and then when you cut out all but one and it does what you describe, it sounds like it is being over-loaded. This would drop the voltage while appearing to be under load. Also, your wiring switching to one alternator could be causing the remaining alternator to be sending power into the alternators not being used which would be a large current drain on the working unit.

Again, you have a great opportunity to power your home with this much hydro power if you bite the bullet and purchase the correct equipment.

Good luck!

Jeff Yago


Recharging batteries using a wood stove

Friday, February 20th, 2009


We live in a small cabin and rely on deep cycle batteries to power our lights. The wood stove is going pretty much 24/7.Is there any way to make a battery charger to sit on the wood stove and make enough energy to charge one battery at a time?




I have an electric fan device that sits on top of our wood stove and the unit generates electricity from the heat to run the small fan.  Unfortunately, you get only a very tiny amount of electricity from this solid state thermal energy conversion process, and all the electrical equipment must be able to withstand the high temperatures.   Yes, you could get enough electricity from wood stove to do this, but the cost and size of the equipment to do it would be un-realistic.   Your best bet is to spend your money on solar modules.

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



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