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

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Archive for the ‘Charger’ 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


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


Gel-Cell Battery Charger

Sunday, December 14th, 2008


Thank you for all of your help in the past. Is there a particular charger you would recommend for charging a small battery bank of 2 Gel-Cell batteries (183aHr, wired in parallel)? I would really need one that is capable of trickle charging over a couple months unattended, as well as the ability to set a dip switch or other selector to have it charge regular auto/ marine flooded lead acid batteries.

I almost purchased a Samlex SEC1215 but figured I should check w/ the expert first.


Matt Houghton


There may be a charger that does both, but it does not seem very energy efficient. Most battery-maintainer type “trickle chargers” are very small and use very little electricity. They are designed to just off-set the standby losses for a battery bank not being used, and they are designed to use only a tiny amount of purchased electricity.

There are larger battery chargers that have switches to select from heavy charging to lower charge rates, but most do not go as low as you are needing and even if they did, they most likely would require much power to run in this low charge mode since you are dealing with larger capacity electrical components not being used at their rated output. There is nothing wrong with having two chargers on the same battery bank. Keep the trickle charger on full time, and use a larger charger when you need a fast re-charge after a heavy deep discharge.

The following link is for the unit I have used on several projects with good results. Its not a high dollar model, but seems to do a good job at a fair price.

Good Luck,

Jeff Yago


Generator puzzle

Friday, November 28th, 2008

I have a Yamaha 1000 watt generator. If I plug in my battery charger or even if I use the generators battery charger mode, my deep cycle battery does not charge as full or as fast as it does if I use my household 110 outlet.

Why is this ? Both are 110 Volt sources.

Jim Mowatt

Actually they both are NOT 110 volts as you suggested. AC power is alternating current with the voltage going from a maximum negative value to a maximum positive value, which makes this reversing of polarity 60 times each second. If you could see this voltage it would form a perfect sinewave curve with half above a zero voltage and half below. When you connect a voltmeter it will read 110 to 120 volts depending on your utility supplier, but the meter is reading the “average” voltage since the meter cannot move fast enough to display what the actual voltage is for that fraction of a second. If you use a special root-mean-square (RMS) type voltmeter, it will actually read 169 volts, which is the voltage between the highest and lowest peak of the sinewave curve.

Now comes the rub. When you start plugging more appliances or lights into a wall outlet, this 169 peak volts remains solid and does not “lug down”. However, all lower cost and smaller generators will start lowering this 169 peak volts as you add more loads to the generator. This is how these generators handle heavy loads and avoid damage.

Unfortunately, almost all battery chargers are designed to utilize ONLY the top peak and bottom peak area of this voltage sinewave, which means any drop below the 169 RMS voltage will cause the charger to not function at all. There are battery chargers and inverters designed to operate from generator power without any problem, but if your charger does not specifically say so then it will not. There are also high end generators that do not have this voltage drop problem. For example, the Honda generators that have an “i” after the model number means the generator includes a built-in inverter circuit to maintain a perfect sinewave output and should power any battery charger or anything else as long as it does not exceed its load capacity.

Finally, regardless of the battery charger you have, I would not expect any 1000 watt generator to have enough capacity to charge a bank of deep cycle batteries. You will need to replace either, or both, the generator and charger, depending on their design.

Good luck,

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


Inverter and battery charger question

Thursday, August 28th, 2008

Hi Jeff,

Thanks for being such a great resource. I’ve had fun reading your archives. I have an inverter question and a battery charger question.

1) I’ve heard inverters are most efficient when operating near their max wattage, so I’m wondering if it’s better to run small stuff from a small inverter. I have a 350w inverter for lights and computer stuff, but I plan to buy a 1500w inverter that can run our well pump when the power is out (which is pretty often). Can I hook them both up to the same battery bank so I can plug in selectively to the one that is most efficient for the job, or should I just run everything off the 1500w inverter.

2) My battery bank will have more solar power eventually, but for now when it needs a quick boost I’ll need to charge it up with the 10amp car-battery charger. Will this hurt the charge controller, inverter and DC circuits attached? Or can I just slap the car charger on the battery bank as it sits.

Thanks a bunch,

Steve Sonntag MD

Not sure why you want to charge the batteries with a 10-amp car battery charger as this will take forever. The the battery charger built into most inverters is much faster and will do a better job of providing the proper charge without battery damage.

The answer related to using two inverters will depend on their quality and size. Yes, some people use dual inverters, with a small inverter taking care of a group of smaller loads that run more often, and a larger inverter for the larger loads with less run time. However, I have used some “cheap” small inverters that consumed more battery power just sitting there with no loads turned on, then some of the larger inverters that have a low energy “idle” feature. If you are planning to purchase a new inverter and can select one with a very low idle or standby energy usage, you may be better off to just use it for all loads and get rid of the smaller model.

If you are planning to purchase a larger inverter that is a modified sine-wave model, these do great on larger loads like well pumps, furnace fans, power tools, but have problems with some electronics, computer printers, and light dimmers. In this case, you can buy a small “pure sine-wave” inverter to handle your sensitive electronics, and use the modified sine-wave inverter for your well pump. Also remember that most existing well pumps are 240 VAC and most inverters are 120 VAC, so you may need a transformer or will need to replace your well pump with a 120 VAC model, and most likely if you do this you may discover the wire run to the well was sized for a 240 VAC pump and will be under-sized with double the voltage drop when using a 120VAC pump.

Yes, you can wire each inverter to the same battery bank, just make sure each one has its own dis-connect switch and circuit breaker or fuse, and make sure these are rated for DC service. AC fuses and AC circuit breakers cannot be used safely on DC circuits -trust me on that one. However, the SquareD “QO” line (not Homeline) circuit breakers are dual rated for up to 24 volts DC and can be used if that is all you can find.

Yes, you can attach a battery charger to a battery bank while a solar charge controller is also charging and connected. The solar charge controller “looks” at the battery voltage to decide when to put more charge into the battery bank. If the battery voltage is high during charging by another charger, it just decides the battery is full and shuts off. If you have other DC lights or DC appliances connected to the same battery bank, remember these can be damaged if you set your charger voltage higher than the voltage rating for these devices. This is a real concern during battery equalizing charging as this requires a much higher charge voltage than normal charging.

Hope this helps,

Jeff Yago


48 volt battery bank and a 12 volt charger

Saturday, July 19th, 2008

Hi Jeff,

Great read and your knowledge seems to be tempered with a fair degree of wisdom.

Now for the unwise question. What would happen if I connected a 12 volt charger to one battery in the middle of my 48 volt battery bank? Would the input equalize over the whole bank or would I be damaging the charger and/or the batteries.

Currently the batteries are connected to an UPS.


Kindest regards

Brendan Kehoe


First, it would depend if the individual batteries are 6-volt or 12-volt that make up the 48-volt battery bank.

Assuming they are 12-volt and you connected a 12-volt charger to just one battery, the current would flow just through the one battery as this is the only complete circuit. The balance of the battery bank does not complete a circuit that would “circle back” around to the charger unless you connected the positive and negative leads together and that would be a very very bad thing – melted cables and possible battery explosion!

However, I don’t know why you would want to charge just one battery. Lets assume you charged this single battery to a state of charge higher than the other batteries in the battery bank. As soon as you connected the battery bank to a load, this would immediately “draw-down” the higher charged battery because all the cells will try to reach the same voltage level.

This is what happens when you equalize a battery bank. Any already fully charged cells will “boil” off gasses until the lower charged cells reach the same level of charge. I see no reason to do this unless your 48-volt battery bank is not being charged and you only have a 12-volt battery charged and are trying to charge each battery separately.

Its not good to have any battery in a string that is charged much higher than the others.

Hope this helps,

Jeff Yago



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