Re: Battery Question II

On Fri, 03 Mar 2006 12:24:04 -0700, Gio <giomedici@xxxxxxxxxxx> wrote:


So is it OK to use the alternator as a bulk charger in camp, the only
drawback being somewhat lower battery life? Or is this an undesirable
strain on the alternator too?

The answer is, it depends. If your truck has only a light duty
car-type alternator then the alternator can easily be burned up. It
took me several alternators on my rig to get motivated enough to
install a heavy duty one. If you have a heavy duty, continuous duty
rated alternator then it can be used to charge the house battery with
no problems. If the wiring between the alternator is heavy enough
then the battery will charge at max amps (bulk charging) for awhile
but it won't fully charge. The problem is that the voltage setpoint
of the alternator is not high enough to finish the bulk charge or
perform the absorption stage.

I've been working with a group member via email on just this type of
problem. Here are some messages that I sent him, each separated by a
---------. This should answer all your questions. If not, ask away:

----------
....If not, is it [the current converter] something that I should upgrade?

Yes. I recommend the Progressive Dynamics Intellicharge converter
with the optional Charge Wizard. The Intellicharge without the Charge
wizard is a dumb charger. With the Charge Wizard it is an intelligent
multi-stage charger with a maintenance mode and periodic equalization
charge.

This model is available in versions up to 80 amps. I have a 60 amp
version in my rig and love it. Given the load you want to drive and
the necessary battery capacity, I recommend getting the 80 amp
version.

The smart charger cranks 80 amps (or whatever its rating) into the
battery anytime AC power is available until the battery is about
50-80% charged, depending on battery parameters. Then it tapers down
and finally switches to a float mode. Additionally, with the Charge
Wizard, the battery is periodically given an equalizing charge which
greatly increases its life.

If you have a typical Magnetek 6300 converter, you don't have to do
any mods. Just connect the Intellipower to the battery with short,
heavy cables and plug it in. The Magnetek charger will still be
connected but it won't be doing anything under normal conditions. If
the rig is to be parked with shore power applied for an extended
period, removing the fuse to the charging part of the Magnetek is a
good idea to prevent over-charging the batteries.

-----------------

The battery charger in the coach is a 55 amp Magnetek 7455. I also
have a Hughs auto transformer that we use when plugged in.

That's a dumb converter, although it is a switchmode version. It
can't do a smart charge and will not completely charge the batteries,
leading to premature failure. It is primarily designed to supply 13.8
volts to the house's 12 volt system.

I'm very interested in adding batteries under the dinette. Would I have to
build some kind of box under the seat?

I have mine in a pair of marine battery cases. Some sort of case is a
good idea to contain any acidic mist that emits from the battery. It
won't generate enough hydrogen to have to worry about venting the
space.

I bet the wires will be huge.

That depends on what load you're driving. If you want to use that
1500 watt inverter I mentioned above then #4 or #2 welding cable would
be appropriate. Heavier cable if the length is much over about 4 ft.
A major advantage of having the batteries under the dinette is that
you can also locate the inverter there. With a 1500 watt inverter you
can run your microwave oven, the coffee pot or anything else that
draws under 1500 watts.

Are all
your batteries on line all the time? How many batteries can a coach charger
charge?

Yes, I have all online at once. In the winter I use an electric
blanket that draws about as much power as your CPAP. With 3 group 29
batteries, I have no problem at all running all my loads. I like a
lot of light at night so there are usually several fixtures on
including a 55 watt reading light.

I'll typically use 150 amp-hours during a winter day. I can put that
back in with about 2.5 hours' running of the generator and the 60 amp
Intellipower.

Any charger can charge any amount of batteries as long as the voltage
matches. It's just a question of how long. A 1 amp charger could
charge a 400 amp-hour bank but it would take 400 hours.

If you install 3 group 29 batteries, you'll have 125*3 = 375
amp-hours. The 60 amp Intellipower would charge those from a 100% DOD
in 375/60 = 6.25 hours. In reality you won't go to 100% DOD so it
won't take that long.

OTOH, the smart charger starts backing down the current at about 80%
charge (multiple paralleled 12 volt batteries) so it'll actually take
a little longer than the straight calculation above would indicate.
For the 164 amp-hours that I computed your CPAP would use, one could
replenish it in 164/60 = 2.7 hours. Figure 3 hours. An 80 amp charger
would do it proportionally faster.

I'll have to measure the battery tray and the area under the dinette. Then
find a route for the wires. Hmmm, at bit bigger than speaker wires....<VBG>
BTW are 6 volt golf cart batteries deep cycle by design?

yes. but they're not rated for a high discharge rate. I have a 72
volt bank of GC batteries in my electric car. It draws over 400 amps
at full throttle from a start. The pack voltage drops to around 50 at
that load and I'm severely shortening their lives. I went that route
strictly because of money - that many golf cart batteries were cheaper
than any other way of getting 220 amp-hours at 72 volts. I can
replace the GC battery pack a couple of times for the price of
batteries rated at 400+ amp discharge rate.

Would I want to just upgrade the 12 v batteries in the original tray and
then add two 6v under the dinette. Please explain all this for me...

In theory that would work but in practice, the battery characteristics
are enough different that it would probably not be very satisfactory.
I'd much rather go with 3 or 4 Group 29s.

My batteries need replacing (about 4 years old) and I think I'm going
to add a 4th battery. I'd like to be able to do a whole weekend
without recharging. I think I can do it with 4.

Lastly, I urge you in the strongest terms possible to get a Link-10.
This is the ONLY way you can know what your battery's state of charge
is and how much energy you have left. This knowledge is doubly
important since you're relying on the pack for health-related power.

Here's a pretty decent place to buy one:

http://www.evparts.com/shopping/product_details.php?id=&product_id=1048

You might find one a little cheaper if you look but he usually has
them in stock for quick shipment.

--------------------------

If you have the generator to run it, I'd go ahead and get the 80 amp
version of the Intellicharge, considering your application.
80*14.7volts = 1176 watts,figure 1250 for efficiency losses. Those
little 1kw ChiCom generators won't quite run an 80. Of course, if you
have an Onan or something, no problem. Otherwise you'd need an EU2000
or something similar.

Here's something else you can do to charge your house batteries at max
amperage while the vehicle's engine is running. Get another Sam's
Club 1500 watt inverter and hook it directly to your vehicle's
alternator. Run a 120vac cord back to the Intellipower, through a
DPDT transfer switch or relay(to select shore power or engine power)
if you like. When you're underway, the inverter will power the
charger. The charger will do a full power, full speed intelligent
charge using the alternator power as the source.

This might sound inefficient and I suppose to some extent it is. But
it neatly solves all the problems of trying to rapidly charge house
batteries from the engine alternator - trying to get enough voltage to
do the job without burning out lights, minimizing the voltage drop
through the wiring between the alternator and the house batteries,
smart multi-stage charging, etc.

This is the config I have on my rig, only with an older 1kw inverter
and a 60 amp Intellipower. It works GREAT. My old rig (small
motorhome) had a car type alternator that I had to upgrade to handle
the high load but once that was done, I see a solid 60 amps going to
the house batteries anytime the engine is running.

This is especially good if you have a truck and trailer because you
only have to run light gauge 120vac wiring between the truck and
trailer. You can put an ordinary outdoor 120vac outlet at your
truck's electrical hookup point and an ordinary extension cord on the
trailer. And, of course, you have a nice inverter in the truck for
powering other things when you're not camping.

Ideally you'll connect the inverter's 12 volt feed through a relay
that is operated by oil pressure or alternator output. That way the
inverter won't draw power when the engine is off and it won't be
connected until the engine is up to speed and hopefully the alternator
has stabilized.

--------------------------------

Ok John,
I'm ready to buy the PD. 60 amps and 80 amps are blowing my mind though. Wow, is that a lot of current or what?
Just be patient with me here. It's not the 30 bucks. It's another 20 amps of current running around. <VBG> So, if I get the 80 amp PD, it will charge my batteries at 80 amps and if I get the 60 amp PD, it charges at 60 amps?

Yes.

Oh BTW I have a onan 5kw genset. Now, if I'm plugged into ground power, are the batteries charging at 60 or 80 amps too?

Yes.

Now here's my brain fart qquestion... If I do the engine alternator thing with the ac cord.... how much current is flowing through that cord???

Remember the 10:1 ratio between 12 and 120 volts we discussed for the
inverter? It works the other way too. For 80 amps at 12 volts into
the inverter, that would be about 8 amps through the 120 volt cord. A
16 gauge cord would handle that just fine.

Anyway, will that be in addition to the charging of the house batteries that MH engine alernator is automatically doing now?

With the inverter/converter method I described, I'd isolate the house
batteries from the vehicle charging system. Let the Intellipower
handle the whole job. You'll get much faster charging and longer
battery life that way. An added advantage is that your batteries will
be charged intelligently and at the maximum rate literally any time
there is power available - engine power, shore power, generator power.

BTW my current converter/charger 7455 is 55amps.

The problem is that the 7455 can't deliver much of that current to the
batteries. Here's the deal. During the first phase, called the bulk
phase, the charger operates in constant current mode. The battery's
voltage starts at below 12 volts and rises as charge is taken in. At
about 14.7 volts, depending on temperature, the bulk phase ends, the
charger regulates at 14.7 volts and the battery draws a decreasing
amount of current. This is called the absorption stage. The bulk
stage ends at between 50 and 80% charge, depending on the battery
type. Closer to 50% for GC batteries, closer to 80% for paralleled 12
volt batteries.

The absorption stage runs to about 80% charge or maybe a little more.
The definition of the end of absorption varies but the generally
accepted end is 1% of the initial rate. If the battery was accepting
80 amps at the end of bulk, then the end of absorption would be about
1 amp. When the absorption stage is over the current drops rapidly so
the exact definition isn't terribly important. Some chargers even
regulate the absorption stage strictly by elapsed time.

At the end of absorption, the voltage drops back to 13.8, again
depending on temperature, and the float stage begins. Some chargers
run the float indefinitely, others turn it on and off. The gassing
point for ordinary wet non-maintenance-free batteries is about 13.4
volts so the batteries will gas a little and consume some water at
13.8. The better chargers will cut back to about 13.4 after several
hours of float or turn off completely, pulsing back on when the
battery voltage drops below some setpoint.

If you have a dumb charger, that is, one that only outputs one
constant voltage, then that voltage has to be selected to accommodate
several conflicting requirements. The voltage needs to be high to
completely charge the battery. But if it's high, the battery will gas
when fully charged. And incandescent lamps will burn out rapidly. The
life of an incandescent lamp varies as the THIRTEENTH power of
voltage. Just a little over-voltage goes a long way.

Most dumb converters are set to 13.8 volts at 70 deg, a good
compromise. Auto lamps are actually designed for that voltage because
that's what car alternators regulate at after warmup. The battery
will consume a little water but not too much. The battery won't
completely charge but it'll do OK while suffering a shortened life and
lower capacity.

The ideal setup is as the Magnetek 7200 series converter/chargers do.
When on shore power, the battery is isolated from the house via a
changeover relay and is charged via a built-in smart charger. The
house is supplied with a fixed 13.8 volts from a separate output on
the power supply.

We haven't discussed this aspect yet. If your existing setup doesn't
have a changeover relay, we'll need to add one. This relay will have
a 120 volt coil and will be powered by shore power. When energized,
the battery will be isolated from the house and the house will be
supplied by your old converter (you leave it in place.) When there is
no shore (or generator) power, the relay connects the batteries to the
house wiring.

The P&B PRD type relay
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=275864&e_categoryid=155&e_pcodeid=65505
is the type to use. This is the same relay used in RV automatic
shore/generator changeover relays. Mouser's kinda high priced but I
have them bookmarked for easy reference. The one I'm referencing
above has a 12 volt coil. You'll want a 120 volt coil. Just change
the part number to -120. These relays are commonly used in HVAC so
your local HVAC parts supplier probably stocks them. Look at the
photo in that link so you'll know what to ask for.

If all this isn't clear, I can sketch out a schematic and send it. I
need you to look at your power center (where the breakers and fuses
are and where your existing converter connects) and tell me what you
have. Preferably with a photo or two if you have a digicam.
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN
A foolish consistency is the hobgoblin of little minds.-Ralph Waldo Emerson
.

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