[NSRCA-discussion] Electrics

Thu Apr 20 13:03:31 AKDT 2006

Bill,

  He is probably right about most people overcharging batteries.

  The big difference in charging, compared to NiCads, is that you do NOT charge by current, you charge by voltage.

  Nicads are traditionally charged by constant current, the voltage varies during the charge, and the voltage is used by peak chargers to determine when the charge is complete (negative voltage delta).

  Lead-Acid batteries should be charged using a constant-voltage method (and current limited, at least initially). However, as the charge level comes up, the current will drop, but the ability of the battery to accept a charge diminishes, and if the voltage is kept at a high level the electrolyte will boil and the level will drop, requiring frequent addition of distilled water. If the cell is sealed, excessive pressure could develop.

  If the float charge (more appropriate than calling it a "trickle" charge) is kept at 13.2v, then very little boiling and/or pressure will develop, and will require much less maintenance. However, 13.2v is not enough voltage to equalize the cells, and would take several days to charge a battery anyway.

  The best option is to use a multi-stage charger that automatically reduces the voltage over time. This is what the converter in my RV does, it starts at 14.4v for a couple of hours, drops to 13.6v for normal operation, then drops to 13.2v after that.

  One alternate option is to use a low-cost automotive type battery charger to perform the initial bulk charge (preferably one with an automatic cutoff), then switch to a "Battery Tender" type of charger, one that maintains a 13.2v level. The nice thing about a battery tender is that you can parallel multiple batteries to maintain them, once they have been normally charged.

  Bob R.

Bill Glaze <billglaze at triad.rr.com> wrote:
      Bob:
  Some time back I was reading a non-model airplane publication, (shame, shame!) and the subject was lead/acid auto type batteries.  The author stated that virtually everyone that trickle charges this type battery "overcharges" them; he stated that the continuous charge should be in the single digit milliampere range to prevent long-term damage.  (Presumably 9 mils or less.)
  Comments?  From anybody?

  Bill Glaze
    ----- Original Message ----- 
  From: Bob Richards 
  To: NSRCA Mailing List 
  Sent: Monday, April 17, 2006 3:37 PM
  Subject: Re: [NSRCA-discussion] Electrics

  Nat,

  For the gel cell you mentioned, the specs show a lower voltage recommended for continuous charging, somewhere around 13.3v. For a typical vented wet-cell battery, 13.6 would not damage it, but you would have to check/add water more often. The gel cell may build up too much pressure if left on charge at 13.6v for too long.

  I'm not sure about the Iota, but my PD9145 came with a "Charge Wizard" which makes it a multi-stage charger. I assume the Iota has something similar.

  You would probably be ok at 13.6v for several hours, but you would want to put it on a float charge after that. Something like a Battery Tender would do that.

  Bob R.

Nat Penton <natpenton at centurytel.net> wrote:
      Bob, Wayne
  My Iota shows an output of 13.6v. Is this too much for continous charging of the lead acid ? I did'nt buy the Iota attachment for auto charging the lead acid. Do I need it and what does it do.                Thanks      Nat
    ----- Original Message ----- 
  From: Wayne Galligan 
  To: NSRCA Mailing List 
  Sent: Monday, April 17, 2006 9:50 AM
  Subject: Re: [NSRCA-discussion] Electrics

  Bob,

  All good points.   We see many battery failures in the car business due some or all of what Bob stated.  Sulfating being the main culprit caused from low charge and overheating conditions.  Also the "NO Maintained" batteries will also get low on water causing failure of the battery.  If you find your battery low on fluid add only DISTILLED water.  Lead acid or gell cell batteries work best when kept at near or full charge. 
  I am adding a battery to my trailer and I am gong to use a solar powered device to keep it at full charge status.  See this link.  http://oil-tech.com/catalog/index.php?cPath=1_27_28&osCsid=942e0092cd33b4ed5abc90e57ca8eca7   It is called the SOLARGIZER.

  Wayne Galligan

    ----- Original Message ----- 
  From: Bob Richards 
  To: NSRCA Mailing List 
  Sent: Monday, April 17, 2006 6:19 AM
  Subject: Re: [NSRCA-discussion] Electrics

  Nat,

  I've learned a lot about the care and feeding of lead-acid batteries the last couple of years, from having to replace one in my camper a couple of years ago.

  First, don't discharge 100%. For the longest life, try not to discharge below 50% capacity. That means get a bigger battery, or more of them.

  A "marine" battery is not a true deep cycle battery. It is usually a compromise between a standard starting battery and a true deep-cycle battery. For best deep-cycle performance, get a pair of 6v golf-cart batteries. They are usually a little taller, have much thicker solid plates, and can be discharged many more times than marine batteries.

  Don't even try to use a conventional starting battery for deep-cycle applications. If you really want to use the battery in your car to charge from, install a deep-cycle battery, but go up about 25% or more in size. Deep cycle batteries can be used for starting, but for the same size they don't have as much cold-cranking amps, hence the larger size required. Conventional starting batteries have porous plates, the additional surface area helps to increase the cranking amps, but deep-cycle use will cause sulfation that clogs up the pores and quickly reduces the cranking amps.

  Sealed or gell cells are not good for deep cycle use, or so I have been told. They typically are used for standby power sources, due to their low maintainance. They can't be charged as quickly since pressure builds up and can't be vented.

  AGM (absorbed glass mat) batteries are good, but cost 2-3 times as much as similar sized vented wet cell batteries.

  The only way to truly determine the charge state of a lead acid battery is to measure the specific gravity using a hygrometer (sp). You can measure the *resting* voltage to determine the charge state, but the battery must remain disconnected from any load/charger for some time for this to be anywhere near accurate. Basically, 12v or less is discharged, 12.7 is fully charged.

  Always store a battery fully charged. When a lead-acid battery is discharged, sulfation will occur. Immediately charging the battery is supposed to help get rid of the sulfation, but the longer you wait, the harder it is for the sulfation to be reversed.

  The best chargers are ones that have 3 or 4 stages. You can start with a charge voltage of 14.4 volts, but after some time the voltage should be reduced to 13.6, and for float charge it should be reduced to 13.2, which can be left connected indefinitely. Some chargers have a cycle that sets the voltage to 14.4v for several minutes every few hours, which helps to stir the electrolyte (not needed in AGM batteries).

  You can charge to 80% capacity in about 4 hours with a good battery and charger. The last 10% of charge can take 24 hours or more.

  Some of the best chargers are actually converters made for RV use, and they also double as 12v power supplies. Iota and Progressive Dynamics are two good, popular brands. I installed a PD9145 in my RV.

  I hope this helps.

  Bob R.

Nat Penton <natpenton at centurytel.net> wrote:
          The only battery giving me a problem is the lead acid Marine 'deep discharge'  battery used for field charging of the lipos. It has lost about 70% of it's capacity in seven months.

  It provided six 12min flts when new and was purchased from Academy Surplus for $40. It has provided a total of maybe 80 flights ( 30 cycles ??? ). The problem is likely due to my maintenance ( lack thereof ). I left the battery in a partial discharge state sometmes for weeks. You can find maintenance needs on Google at agmbatteries, courtesy Earl Haury.

  West Mountain sells a gell cell, 54#, 84ah, rated for 500 cycles @ 100% discharge ( 20hr discharge rate ), $149 del. I will see how it performs under our conditions.
                                                        Nat
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