Date: Sun, 25 Jun 2006 15:25:42 -0700
Reply-To: Mike Elliott <j.michael.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike Elliott <j.michael.elliott@GMAIL.COM>
Subject: Re: Making an alternator a smarter charger? [LVC]
In-Reply-To: <000001c698a2$11087a50$6400a8c0@masterpc>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Dennis, I hadn't considered the effect of 14 - 14.8 absorption voltage
on the headlights and other driving devices in the Vanagon. That's a
darn good point. If a fellow had a second alternator for charging the
deep-cycle house battery, then a smart regulator like this might make
more sense. But with a single alternator and knowing that the lifetime
of an incandescent bulb is proportional to the 12th power of the voltage
overage or underage, I'll think I'll take a pass on this device.
Your point about spending that money on a second battery is a good one,
but when I'm climbing a 7% grade for several hours in 90F weather in a
1.9L WBX, every pound I carry adds to the engine load. This may be my
years of lightweight backpacking talking, but Group 31 and T-105
batteries weigh 65lbs . . .
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR
On 6/25/2006 2:55 PM Dennis Haynes wrote:
> I have stated many times in the past that the alternator is not the best
> method for charging a deep cycle battery. However, the situation is not
> that bad. Let me try to explain things a bit further.
>
> Most of the capacity of a battery is returned during the "Bulk" part of
> the cycle,(~80%). The current delivered is usually limited by the size
> of the charger. The charger should be selected to charge the battery at
> an 8-10 hour rate. Now, here is where it gets confusing. An alternator
> tries to deliver a fixed voltage, not a specific amount of current. This
> voltage is needed to feed all the other loads. If the wiring and
> controls are up to snuff, the alternator will probably bulk charge that
> group 31 battery at ~ 25-30 amp/Hours, (3-4 hour rate). Guess, what,
> that is to fast for long battery life. The cell voltage will rise
> quickly and meters will indicate the battery is at a higher state of
> charge ten it really is. Now the alternator can't be told to lower the
> current because than system voltage can drop and this will cause all
> sorts of problems with accessories and lights.
>
> Now using an alternator, we really go from bulk to float. If we float
> long enough, it is not an issue to skip absorption as long as we
> periodically equalize. 13.8 volts is basically the ultimate float
> voltage as it can be withstood almost indefinitely by a healthy battery
> as long as the electrolyte is regularly checked. Really smart chargers
> will drop the float down to ~13.2
>
> Now for that absorption stage, this is where that alternator controller
> shines, however, for automotive use it can have some problems. One
> thing, maintenance free starting batteries don't need or like 14.8
> charge cycles. Neither do all your lights unless you have voltage drop
> issues. Imagine 15 volts on your accessories. The alternator won't like
> that load for long also.
>
> For absorption and equalize charging, get a good charger and use it when
> shore power is available. The will keep the battery healthy and happy.
> If you're driving for extended periods, the float charge will work and
> the bulk porting will work the alternator enough. Make sure you have a
> good ground directly to the alternator.
>
> My motor home has a 2,500 watt inverter/100 amp charger with true 3
> stage operation. On occasion, we will start the generator to operate the
> roof AC's while driving. When that charger starts reaching 14.8 it does
> a number to all the indicator lights through out the coach. Same problem
> if I pull into a campground and plug in while still using everything.
> Fix is to change the profile to limit absorption to 14 volts if I am
> using stuff. Guess, what, that brings me almost back to basic float
> charging.
>
> OK, so what am I saying? That is a great device and it has its
> advantages. For Auto/RV use some of those advantages are limited. For
> your money, if the battery you have still does not do the job, this
> device at best will add ~10-15%, so use your money for more battery
> capacity or do with less power.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
> Of Michael Elliott
> Sent: Sunday, June 25, 2006 12:55 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Making an alternator a smarter charger? [LVC]
>
> Hi electrical and lead-acid wizards,
>
> I've installed a nice Group 31 flooded cell deep-cycle "house" battery
> under the bench seat in Mellow Yellow, along with all the requisite
> hefty 6-gauge wiring to reduce voltage loss, and a sturdy relay to
> disconnect the house from the engine battery when the engine is not
> running. I'd like the house battery to be fully-charged when I pull into
> camp, so I've been looking at charging algorithms for lead-acid
> batteries and it's clear that an engine alternator is not a very smart
> charger.
>
> There are three common stages to charging a lead-acid battery: Bulk,
> Absorption, and Float.
>
> http://www.rpc.com.au/products/batteries/car-deepcycle/carfaq9.htm has
> some nice charts that show the stages for several types of batteries.
>
> Roughly speaking (I think I have this part correct), after a battery has
> been discharged (in the case of the engine battery, this would be due to
> starting the engine, in the case of a house battery, this might be after
> a day or so of running lights and other loads) the first stage, Bulk,
> dumps current into the battery at a fairly high rate until the battery
> reaches about 14 to 14.8 volts (depending on battery type). The current
> is then tapered as needed to keep the battery from exceeding this
> voltage; this is the Absorption stage, and it is here where the battery
> is getting "topped off." It is also heating and releasing gas. After a
> period of time, an hour or two (according to battery design), the
> voltage is dropped to about to a float voltage of 13 to 13.8 volts
> (depending on battery type and temperature) to keep from overheating the
> battery and damaging it. This Float stage maintains the charge in the
> battery that was achieved during the Bulk and Absorption stages. There
> is also an optional Equalizing stage which is good for some battery
> types -- the battery is occasionally hit with higher voltage to mix
> things up and keep the battery happier longer.
>
> That's the (rough) idea. Near as I can tell, alternators are not real
> smart battery chargers. They are designed to put out the same voltage,
> all the time. They have a high current capacity, when running at higher
> rpms, so they do a good job with the Bulk portion of stuffing a charge
> into the engine battery when the engine is at high rpms (not at idle),
> but they don't have separate Absorption and Float charging stages. If
> you want to fully-charge your house battery by setting the alternator to
> 14 to 14.8 volts (using, maybe, one of those Barton Harness adjustable
> regulators that mount on the alternator [thanks Mark Drillock]), the
> battery will start to overheat after a few hours (depending on battery
> type) because it never drops into the lower voltage Float stage. To
> avoid that, the alternator can be set to output 13 to 13.8 volts, but
> then the battery never gets that Absorption stage that fully charged it.
>
> So I'm looking Ample Power's Next Step voltage regulator:
> http://www.amplepower.com/products/ns2/index.html
>
> It monitors the output voltage of the alternator, and adjusts that
> voltage according to how you set its Absorption Voltage, Absorption
> Time, and Float voltage trimpots. It also accepts a thermal sensor to
> monitor the temperature and modify charging voltages accordingly. It
> looks pretty cool to me -- does anyone have any experience with it, or
> with a similar device?
>
> --
> Mike "Rocket J Squirrel" Elliott
> 71 Type 2: the Wonderbus
> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
> 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
> KG6RCR
>
>
>
>
| 
