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

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Archive for the ‘Batteries’ 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?

Thanks,

Bob Kruckenberg

Bob,

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

Jeff,

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.

Thanks.

Bob Libbon

Bob,

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

Jeff

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

Tom
Indianapolis

Tom,

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

Jeff,

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?

Thanks.

Sam Allen

Sam,

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

Jeff,

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

Sam,

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

Jeff,

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?

Thanks.

Mark

Mark,

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

 

Replacing one old battery in a string

Thursday, May 7th, 2009

Jeff

What’s the procedure for replacing a single “bad” battery in a bank of batteries with a few years on them?  Looks like a good opportunity to create a significant imbalance.

Dick

Dick,

If you install a “new” battery into a string of older batteries, you can be sure it will immediately “assume” the charging capacity of the rest of the string since they will determine the charging voltage and charging current.    In other words, after a few weeks of charge/discharge cycling it will act like its the same age as the other batteries.

I have replaced a bad battery in a string that was less than a year old with good results, but think it would be a waste of money to do this for an older battery bank, as its best to replace all at the same time.  A battery bank is just like a chain, its only as good as the weakest link.

Good luck,

Jeff Yago

 

Batteries making too much water

Wednesday, May 6th, 2009

Hi Jeff,

Great website!  Found it through Google search.  Since you have a lot of experience with solar battery applications, I wanted to share my battery experience to see if you have heard of this before:

My wet cell marine batteries I use for storing my solar energy are constantly making excess water in their cells, which forces me to drain out some electrolyte every month, otherwise the batteries will spill electrolyte onto my garage floor (definitely bad for the concrete).

Have you heard of this phenomenon before?

Thanks.

Benjamin Day
Alhambra, Calif.

Benjamin,

Assuming you are not trying to put one over on me, this is not physically possible.  Batteries do not “make water” during the charge/discharge process.  A liquid acid battery contains lead plates and a mixture of water and sulfuric acid. During charging, part of the water is converted back into acid and the mixture will gain in acid content, but not volume.  During discharge, the acid does get converted into water, but this is a conversion of one liquid to another and not an increase in liquid volume.  The specific gravity changes as this mixture becomes more acid  when fully charged,and more water when fully discharged, but the volume does not change and you are not creating a fountain of water out of thin air.

Here is what is actually happening and I have seen many clients make this mistake.  At some point they decide the water in the batteries appear low so they add more distilled water, but fill almost up to the caps.  Then a few hours or days later their batteries receive a heavy charging cycle.  During a heavy charge, the batteries can get very hot and the lead plates and acid-water mixture inside the batteries also get very hot and expand, forcing the over-filled liquid to bubble up and out the battery caps.  Then when the batteries finally cool, the liquid level is now low and they make the same mistake all over again and add more water.

An almost new battery bank of quality deep-cycle batteries in normal solar use will not need to add water or remove water for almost a year.  As batteries get older, they will need to add distilled water about every 3 or 4 months.  When they are near the end of their life, you may need to add distilled water once a month, which is a good indication that its time to replace.   But I will guarantee you that you have not discovered some device that makes water out of electricity.  You might want to see if a family member has been over-filling water when the batteries are cold, like the neighbor who adds a few gallons of gas to your brand new car when you start bragging about the great mileage, then when he stops playing his joke you take the car back to the dealer wanting to know why you are no longer getting 75 miles per gallon..

Good luck,

Jeff Yago

Thanks, Jeff for your very in depth reply!

I can guarantee you I am not joking. Reason I was concerned is I read about plates swelling up, and thought my plates might be trying to tell me something. I can’t physically see them as they are underneath a plastic diverter in the fill tube.

I seldom let my batteries charge very long on my solar controller’s equalization charge level of 14.1 V (when the bubbling of oxygen and hydrogen gas can be heard), as I use my stored electricity every night and bring my battery voltage down to about 12.1 V before disconnecting the load.

So this will remain my mystery – I’ll let you know if I suffer catastrophic battery failure in the future – then the world will know if this battery symptom is a sign of something worse to come!

Again, I really appreciate your reply!

Ben

Ben,

Yes, battery plates do swell up over time, but this would be years, not days, so any plate expansion causing water to flow up and out of the caps would take so long that you would never notice.  When we remove old batteries that have exceeded their intended life,  they usually look like someone connected a pressure hose to the vent cap, as the sides are all bulged out from this  calcium buildup and chemical corrosion on the plates.  I have seen golf cart batteries gain over an inch per side from this plate expansion, but like I said, it takes years for this to reach this extreme.

Good luck,

Jeff Yago

 
 


 
 

 
 
 
 
 
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