Re: House Batteries
- From: "Tony Brooks" <Tony@xxxxxxxxxxxxxxxxx>
- Date: Thu, 12 Nov 2009 10:35:35 -0000
"Tony of Judicious" <tony@xxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:hdgjag$sf$1@xxxxxxxxxxxxxxxxxxxx
Tony Brooks wrote:
SNIPPED
AGAIN
Do the charging regulators, such as the Adverc and Sterling (?), cycle the
alternator voltage to a higher value so as to get the battery near fully
charged?
Do they actually work?
My only experience goes back 20 years when I was doing some extended
cruising on a yacht fitted with an Adverc and it was a load of trouble.
I just knew someone would ask that and unfortunately there is no easy answer
so another long explanation I am afraid.
If you want a quick answer go to the last two paragraphs.
First we need to go back into history and look at alternator outputs. The
Lucas 10/11AC of the 60s had a regulated charging voltage of about 13.8
volts. The ACR follow on series used 14v to 14.2 volts and the later A127
comes with varying outputs from about 14.2 up to 15 volts depending upon the
regulator fitted. Other makes followed a similar development.
Wet, open cell, lead acid batteries start to gas (break down the electrolyte
into gas) at about 14.4 volts and it is "about" and not a definite number.
Sealed batteries must not be allowed to gas as doing so would deplete the
electrolyte with no means of topping up, whilst gel batteries and certain
makes of AGM should not be charged at more than 13.8 to 14.1 volts. This
means that using one of the "charge enhancers" on gel or certain AGM
batteries could end in tears.
When considering charging circuits 0.1 volt difference in charging voltage
makes a much more significant difference to the charging current so
minimising voltdrop on the charging circuit is important. Unfortunately the
diode charge splitters that appeared in the 1960s and continue in use today
will produce a voltdrop of up to 0.7 volt and with typical engine running
times this is guaranteed to ensure the batteries are never fully charged.
Then we have the problem of boat builders believing the current rating on
the cable drum and not doing voltdrop calculations for the length of run.
This leads to more voltdrop as do cheap ammeters (longer cable run), worn
out charge splitting switches & relays and joints in the charging circuit
etc.
Most alternators measure the charging voltage at their output terminal so
voltdrop on the circuit has a bad effect on battery charging. This is known
as machine sensing. Some alternators have an extra wire running to the
batteries and use this to measure the charging voltage at the batteries so
with a 0.5V voltdrop the alternator would see 13.5V at the battery and
increase the voltage at its terminal to 14.5V so the 0.5V lost in the
circuit is compensated for so delivering 14V at the batteries. This is known
as battery sensing.
Perhaps the most important thing the advanced controllers do is to convert
the alternator from machine sensing to battery sensing, but if your system
is in good order with properly specified cables and very few terminals you
should not need to do this. (There is an argument that certain alternators
would still benefit because they measure the voltage at a different point
inside the alternator but this will be a marginal difference in most cases).
Battery charging:
During the first charging phase the alternator's charging voltage will be
controlled by its internal design and in effect the higher the charging
current the lower the voltage the alternator can produce. They should never
be able to produce more current than they can handle so stories about
controllers burning out alternators either point to insufficient cooling
(tight, unvented engine boxes or rank poor design.). During this phase the
charging voltage may only be a bit above 13 volts and gradually rising as
the batteries charge. The voltage is below the regulated voltage and so
both the alternator's own regulator and any additional advanced regulator
just have to sit there unable to influence the charging voltage. This phase
will go one until the charging current has dropped significantly and
typically would be for well over an hour. This is known as the Bulk Phase
and nothing can increase the alternator's output.
Once the charging current has fallen enough the charging voltage will have
risen to the regulated voltage (about 14.4V on a modern alternator) and as
soon as this happens the alternator's regulator will start turning internal
electromagnets on and off very quickly which in turn controls the output
voltage to the regulator's setting. This is known as the Acceptance Phase
and an advanced regulator can now start to mess about with the charging
voltage. If you have voltdrop on the circuit or if you have an older, low
charging voltage alternator an advanced controller will improve the
charging. If you have a very low voltdrop and a 14.4V or above regulator an
advanced controller can make little difference.
During this phase the current flowing into the battery is proportional to
the charging voltage and inversely proportional to the battery voltage so on
the face of it boosting the charging voltage will produce a higher charging
current. Indeed that is exactly what you will see on an ammeter BUT once you
get above ABOUT 14.4 volts the battery will start to gas and some of the
charging current will be used to break down the electrolyte and heat the
battery. I have seen figures that suggest this is a large proportion of any
increase in charging current and the actual effectiveness of advanced
regulators (as opposed to their apparent effectiveness) is open to question
once we use a regulator set to 14.4 volts. This phase will go on for very
many hours. I have seen 16 or 20 hours mentioned for a typical boat battery
bank.
Eventually, after many hours of acceptance charging the battery will be
fully charged and the charging current will have naturally dropped to a very
low figure of perhaps 5 amps or less per bank. This is the Float Phase and
the idea is to prevent self discharging which can be up to 8% of battery
capacity per month.
Some advanced controllers add an extra phase known as Equalisation. This
would be inappropriate for any sealed battery. The controller elevates the
charging voltage to (say) 15 volts for a period. This should ideally be done
manually to prevent battery damage so the settings for an automatic
Equalisation charge will be very conservative. The idea is to re-mix the
acid in the cells and to make sure all the cells have the same amount of
charge, however on a typical boat system the value of this is questionable
but it has one benefit. The higher voltage will help to reconvert some of
the sulphate I mentioned in my last post.
Please note that there are so many variables concerning batteries all
figures can only be approximate.
To specifics. An Adverc cycles the charging voltage between 14.? and 14.5V
in 20 minute periods. This is either side of the gassing voltage and of
shorter duration than it takes for gassing to commence so it should be OK on
sealed batteries. I think they can also be set for specific battery types. I
have fitted an Adverc but am not convinced it makes much difference to the
overall charging. I have since fitted a 60W solar panel and that makes a
significant difference to battery life. (It's far easier to mount a large
panel on the roof of a tin slug than it is on a yacht but all that means is
the wind may be more suitable for you).
A well implemented and maintained charging system with the regulator set to
14.4 volts (or any lower figure specified by the battery manufacturer) is
unlikely to gain major benefits from an advanced controller. A poorly
implemented system with a lot of voltdrop or a system with less than 14.4
volts charging voltage will benefit but a few hours and perhaps £50 for
another alternator regulator (if available) and a few metres of thicker
cable will probably have very similar results.
--
Tony Brooks
www.TB-Training.co.uk
Electrical & Mechanical Training
for ordinary boaters.
.
- Follow-Ups:
- Re: House Batteries
- From: tony
- Re: House Batteries
- References:
- House Batteries
- From: Richard
- Re: House Batteries
- From: Tony Brooks
- Re: House Batteries
- From: Tony of Judicious
- House Batteries
- Prev by Date: Re: House Batteries
- Next by Date: Chirp, chirp
- Previous by thread: Re: House Batteries
- Next by thread: Re: House Batteries
- Index(es):
Relevant Pages
|
