Backup Battery Charging - pros and cons

[Curbie]

Say someone has 48V battery (bank) and inverter and their primary
charge is some alternative energy source (you pick it), what are the
pros and cons of backup charging between properly matched:
1) AC household voltage generator
2) I.C.E. with an automotive DC alternator?

Ulysses does something like this and I've reading through BobG's posts
on OtherPower along the same lines, my overall question is why?

1) Aren't most inverters designed for AC household voltage
generator?
2) If you go with AC household voltage generator, doesn't this
provide additional temporary backup against an inverter failure?
3) Is the I.C.E. with an automotive DC alternator just so much
more efficient for battery charging that it justifies the costs and
hassles?

I don't know maybe I just missing the "Big Picture", could explain
this to me?

Thanks,

Curbie

 

[Bruce in alaska]

Say someone has 48V battery (bank) and inverter and their primary
charge is some alternative energy source (you pick it), what are the
pros and cons of backup charging between properly matched:
1) AC household voltage generator
2) I.C.E. with an automotive DC alternator?

Ulysses does something like this and I've reading through BobG's posts
on OtherPower along the same lines, my overall question is why?

1) Aren't most inverters designed for AC household voltage
generator?
2) If you go with AC household voltage generator, doesn't this
provide additional temporary backup against an inverter failure?
3) Is the I.C.E. with an automotive DC alternator just so much
more efficient for battery charging that it justifies the costs and
hassles?

I don't know maybe I just missing the "Big Picture", could explain
this to me?

Thanks,

Curbie

Well, if it were "Me", I would have Redundant Systems for every phase of
my Power System, AND I DO..... I generate ALL my own power, and live
250 Miles from the nearest "Grid"... So Redunantcy, (is that a word) is
a big deal for "Me"... I have twin 20Kw Diesel fueled Gensets that
generate at 240 Vac Single Phase, and feed my 240 Vac Main Panel. I
then have a pair of 10 Kw 240/120 transformers feed from the Main Panel
and feed the Generated 120 Vac SubPanel. The 120 Vac Generated SubPanel
then feeds a Trace 4024 Inverter input, as well a a few Generated Power
only Loads. The output of the Trace 4048 feeds the 120 Vac Inverted
SubPanel, which has the Main Cabin, and a few Inverted Loads. The Main
Panel also feeds a 24 Vdc 60 Amp Teleco Rated Regulated Power Supply
that can charge the 1200 AmpHour Battery bank that runs the Trace 4024.
I also have a pair of 24 Vdc 60 Amp Truck Alternators, one on each
Genset, that can charge the 24 Vdc Batteries as well. This system gives
me many different path so keep the lights on and place operational,
should any one, or even two, of the elements fail. As a Triple Redundant
Generator, I have an Onan 15Kw RJC Gasoline Fueled Genset, on a trailer
that can be plugged into the Main Panel, should both diesel Genset fail.
I figure I can get whatever parts are required in 48 Hours, for any
Single Failure. so that I am covered fairly well.....

 

[Curbie]

Jim,

What's wrong with a 120VAC transformer-rectifier charger that runs
from the power line or a small generator? I build Variacs and ammeters
into my simple chargers and manually set the current to whatever the
batteries need, according to the temperature / voltage chart on the
wall.

You got me by the tail!

I was thinking that the reason someone go through the hassle and
expense of coupling an automotive alternator to an I.C.E. for battery
backup was purely for I.C.E. to electrical output efficiency?

What are the pros and cons going your route vs. just hooking the
I.C.E. household AC generator to the inverter (both options require
backup gen & inverter)?

Please, go easy on me I'm already confused by all this.

Curbie

 

[Curbie]

Hey Bruce,

If I was in Alaska, with its balmy weather, 250 miles away
civilization, redundancy would be at the top of my list too.

How do you primarily backup change your batteries, one of your AC
generators feeding an inverter or directly by truck alternators,
although it sort of sounds like your primary and backup sources of
power is the same (more redundancy).

Thanks,

Curbie

 

[Curbie]

Jim,

The pros are low cost and rugged, easily repaired equipment, the con
is that it demands personal attention as a substitute for automatic
control.

If you have sometime written up on the construction and use of this
device, I'll see what the expense is in terms of both cost and time.
I've always had a aversion to "turning the crank" on a daily basis,
but I like Bruce's caution regarding redundancy, maybe not 3 levels
but...

Checking the voltage or feeding the stove don't take long but
they don't happen unless I'm home, work + night school meant that my
house fell below 10C in the middle of winter.

I've often wondered why you don't have some solar heating, if I
remember correctly your house loses so little heat, I doubt a system
would to need be very big or expensive?

Curbie

 

[Ulysses]

Say someone has 48V battery (bank) and inverter and their primary
charge is some alternative energy source (you pick it), what are the
pros and cons of backup charging between properly matched:
1) AC household voltage generator
2) I.C.E. with an automotive DC alternator?

Ulysses does something like this and I've reading through BobG's posts
on OtherPower along the same lines, my overall question is why?

1) Aren't most inverters designed for AC household voltage
generator?

I wouldn't say "most", but there are some that have built-in chargers.

2) If you go with AC household voltage generator, doesn't this
provide additional temporary backup against an inverter failure?

Yes. That's assuming you are concerned about inverter failure. I have
OutBack inverters and it's just not something that I think about. I suppose
it could happen, but I have two inverters and can run my whole house from
one so I have a backup. I also have a cheap MSW that I could use to run my
refrigerator if all else failed. And I have a propane refrigerator if I
can't get any electricity.

3) Is the I.C.E. with an automotive DC alternator just so much
more efficient for battery charging that it justifies the costs and
hassles?

Yes. I figured the losses using the chargers in my OB inverters at about
560 watts for each inverter/charger. With my Delco alternator the losses
are only about 200 watts plus some elusive losses due to friction etc via
the belt-drive. With a PMA that 200 watts could be reduced to a fairly
insignificant amount. I don't find it to be much of a hassle. I have my
alternator/charger calibrated so I simply set the engine speed for the
ultimate desired voltage. Plus I have the option of running it at a faster
speed and turning it down once the target voltage is achieved. If I choose
to go automatic with the alternator/charger I could connect it to my OB
charge controller, but then I'd lose more watts.

I don't know maybe I just missing the "Big Picture", could explain
this to me?

If someone is only using a generator occasionally then the efficiency losses
might not be so noticeable. But I generate ALL of my electricity burning
gasoline.

Another factor that is very important to me is the way the OB
inverter/chargers work: they have built-in transfer switches that
automatically switch over to generator power whenever the generator is
connected and running. This results in numerous problems such as nothing
works right and clocks run slow etc. With no significant loads present my
OB inverter, when connected to a generator, will not run my well pump or
microwave oven. The same generator, when connected directly, will easily
run either. I don't know why exactly but there are some huge losses going
on plus some other factors that I can't quite grasp. Not only that but the
inverters are very hard on generators. I have destroyed one generator twice
(got it repaired the first time) and had to replace the wiring harness on
another because it was overloaded and melted, even though I never knowingly
exceeded the capabilities of the generators. Plus the OB system varies the
charging current depending upon the loads present on the inverters. This
results in times when the generator is running with no load, not something
that I like to do. All-in-all if someone was to charge their batteries when
nothing was running from the inverters it may work satisfactorily but it's
just too much trouble for me. But, if the loads are running from the
inverters and the charging is done seperately by an alternator then none of
these problems exist. Everything works fine and there are no concerns about
surges or overloads etc, as long as you stay within the limitations of the
inverters. The load on the alternator is constant regardless of the loads
on the inverters. The output from the OB inverters is nothing to complain
about. Everything runs great and clocks keep accurate time and there are
simply no issues about running anything from them. As long as you don't
connect a generator to them.

OutBack's solution, supposedly, is to use a generator that has twice the
output of the combined total of the inverters. That means I would need a
15,000 watt generator. That also means I would have to run all of my major
loads (microwave cooking, washing machine, air compressor, etc) at the end
of the charging cycle otherwise I would have a huge generator running to
supply only a few hundred watts. To me this is much more of a hassle than
adjusting the engine speed on my alternator charger once-in-a-while. Plus I
don't even know for sure that it would work.

 

[Curbie]

Jim,

It seems options are real important when playing with alternative
energies and since I'm not quite sure where I'll be with some of these
backup systems, I find very helpful to look at these issues from every
possible perspective, thanks for sharing yours.

Curbie

 

[Curbie]

Ulysses,

As I understand your post, both your primary AND backup sources of
power is the I.C.E. with an automotive DC alternator which produces a
far greater battery charge per gallon of fuel that did an AC household
voltage generator through your inverter. Since you have two inverters
you feel comfortable that as long as you can keep your battery bank
charged you should be fine with this setup, which made your greatest
priority in your decision "battery charge per gallon of fuel".

If I got that right it makes sense to me.

When you talk about setting engine speed for the ultimate desired
voltage, is this because you've disabled the alternator's voltage
regulator, so the engine's RPM will dictate output voltage?

Have you read BobG's post on OtherPower:
http://www.fieldlines.com/comments/2009/7/2/154555/8818/1#1

I thought it is a pretty nice place to start on this kind of setup, do
see something I'm missing?

Thanks for the light.

Curbie

 

[Curbie]

Jim,

I tend to assemble cheap versions of all the components and then just use
them and see what patterns develop, before buying a more automatic but
less versatile system.

I ended up focusing on this, is another way of expressing this "test
it cheap, but build it reliable"?

It's important to measure and record performance but you don't need
expensiveequipment for it, I use a KillAWatt and Radio Shack infrared
and remote thermometers and usually log the data manually.

I'm with you on the importance of recording measurements and the use
of a wattage monitor, but the Radio Shack infrared and remote
thermometers are new to me, thanks for that.

Curbie

 

[Bruce Gordon]

Hey Bruce,

If I was in Alaska, with its balmy weather, 250 miles away
civilization, redundancy would be at the top of my list too.

How do you primarily backup change your batteries, one of your AC
generators feeding an inverter or directly by truck alternators,
although it sort of sounds like your primary and backup sources of
power is the same (more redundancy).

Thanks,

Curbie

I run one of the gensets about 10 hours a day in the winter...
8Am to Noon, and 5Pm to 10Pm.... These are the times that I need
240 Vac to be available to run the Clothes Dryer, which is my
Only Real BIG 240 Vac Load. This keeps the Inverter Batteries
charged without letting them get below 20% Discharge, typically.

I also have a second Trace System that runs all the ISP Hardware
for my MicroISP, here, that serves the Close Neighborhood.
(Close= 10 Sq Miles) That System is based around a Trace 2624
with 800 AmpHours of AGM Batteries, and is feed off the 240 Vac
Generated Main Panel, thru a 3 Kw 240/120 Vac Transformer, all installed
over in Winter Shop.

The Teleco System here is provided via a SAT Link, and I am in the
middle of designing a Power system for it, that will be used next winter.
Looks like I need about 500 Watts, 24/7/365 for it, so I am thinking
an Outback 3048 with 800 AmpHours of Battery should do the job, and
still using the same 10 hour/day charging Cycle.

Starting Loads on the Genset are in the 15 Kw Range, but tapper off to
around 5 Kw as the Batteries all come up to Float, so I still have
enough Headroom on the Genset for the new Telco System Load.

Bruce in alaska Pictures are available on my www.99850.net website....

--
Bruce (semiretired powderman & exFCC Field Inspector for Southeastern Alaska)

Bruce Gordon * Debora Gordon R.N. Bruce's Trading Post
P.O. Box EXI Excursion Inlet South
Juneau, Alaska 99850 Excursion Inlet, Alaska 99850
AL7AQ * KL7WJ www.btpost.net www.99850.net

 

[Ulysses]

Ulysses,

As I understand your post, both your primary AND backup sources of
power is the I.C.E. with an automotive DC alternator which produces a
far greater battery charge per gallon of fuel that did an AC household
voltage generator through your inverter. Since you have two inverters
you feel comfortable that as long as you can keep your battery bank
charged you should be fine with this setup, which made your greatest
priority in your decision "battery charge per gallon of fuel".

If I got that right it makes sense to me.

When you talk about setting engine speed for the ultimate desired
voltage, is this because you've disabled the alternator's voltage
regulator, so the engine's RPM will dictate output voltage?

The output voltage is controlled by a combination of the field current on
the alternator and/or the engine speed. I manually adjust (usually only
needs to be done once) the field current for the best results (maximum
output without overloading the engine) and then adjust the engine speed as
needed. The pulley ratio is selectable too but I've found somewhere around
2:1 is about right for my setup. It is possible to simply adjust the engine
speed so that the ultimate voltage will equal your desired Absorb rate (59.5
volts in my case) or Float or Equalize. However, it will take longer to
reach that voltage if charging at a lower rate and I have a pretty good idea
how long it will take based upon experience so I run it faster until it gets
to Absorb, then adjust it so it stays there. If you are using something
like an OutBack inverter/charger you would still need to determine the
duration for your Absorb charging so there's not that much difference
between the two, except the OB is more automatic. If you want to equalize
with the OB system you still have to do it manually.

Other advantages to this type of charger are durability and economical
repairs, as others have pointed out. The engine I'm using only cost $100
(current price is $110) and you can get an alternator for about $35 that has
new brushes and bearings and comes with a warranty. Many alternators and/or
engines may be substituted. Repairs are much simple since there is no
generator head that might need to be removed from an engine, however I would
trade that convenience for a direct-drive setup.

Have you read BobG's post on OtherPower:
http://www.fieldlines.com/comments/2009/7/2/154555/8818/1#1

I don't know if I've read it but I will.

 

[Ulysses]

Ulysses,

Have you read BobG's post on OtherPower:
http://www.fieldlines.com/comments/2009/7/2/154555/8818/1#1

I thought it is a pretty nice place to start on this kind of setup, do
see something I'm missing?

What I read was that there are other alternators that can be used that may
be better than a Delco 10SI. This is something that I have in the back of
my mind for future reference. For the moment I'm content with the Delco
because it will deliver my C10 charge rate and I can have another one in my
hands in less than 35 minutes (assuming the stores are open). Plus I
understand how they work. I have a lot of information on the Delco and it
took some time to accumulate so I would need to do the same with another
alternator. To me the main point that BobG made was the use of double
belts. I have found that a single belt may work OK for up to about 4 HP but
my 6.5 HP engine destroys a single belt very quickly if ran over about 30
amps (at 51+ volts). Right now I'm searching for double pulleys and trying
to learn about the different types of belts. What I end up with will
probably depend upon what is readily available. I don't want to use
something that is difficult to find or obtain if something more easily
obtained will do the job just as well.

Another factor that should be a concern is the power curve of small gasoline
engines. They tend to develop their maximum horsepower very near their
rated operating speed (usually 3600 rpm). Running them at a slower speed to
drive an automotive alternator does not seem to be an issue, at least not
for me. The current output from the alternator is lower (at a lower speed)
so the engine does not have to work as hard and it doesn't seem to be any
less efficient. The whole thing ends up being quieter and the engine is
likely to last longer and need fewer oil changes.

 

[Curbie]

Ulysses,

The output voltage is controlled by a combination of the field current on
the alternator and/or the engine speed. I manually adjust (usually only
needs to be done once) the field current for the best results (maximum
output without overloading the engine) and then adjust the engine speed as
needed.

Do I understand this to mean:
1) The voltage regulator is disabled?
2) How is the field current manually adjusted?
Battery>Rheostat>Atl-F(?)

Repairs are much simple since there is no generator head that might need
to be removed from an engine, however I would trade that convenience
for a direct-drive setup.

Between the gear ratio you're using and engine I can certainly see why
you twisting V-belts, BobG's double V belt & pulley or cogged belt &
pulley is a more expensive route, but should replace you desire for a
direct-drive setup and seems like a must, just too much tension for a
single V-belt.

I get your decision on going with parts you have, but do you think
I'll gain anything going with BobG's setup to start with and learn on,
I'm a little more interested in reliability and long-term cost than
initial cost.

Thanks for sharing your experience!

Curbie

 

[Ulysses]

Ulysses,

Do I understand this to mean:
1) The voltage regulator is disabled?
2) How is the field current manually adjusted?
Battery>Rheostat>Atl-F(?)

Yes, the voltage regulator is disabled. It is simply bypassed and the
connection to the field coil is made directly via the brushes.

I'm just using some nichrome wire (it's what I had on hand) and I *think*
it's about 14 ohms. A rheostat would be a neater way to do it and would be
simple to fine tune. The combined total power consumption of the field
coils and the resistor on my setup is somewhere around 175 watts so the
rheostat would need to be sized accordingly. The field coils are powered by
the output of the alternator from the ground connection and the positive
output and connected directly to the brushes. The 80+ volts that I'm
getting from my setup are reduced, via the nichrome resistor, to somewhere
in the neighborhood of 12-14 volts (I have not measured this voltage for a
long time but it's one of those things that's consequencial--we are more
concerned with the output voltage in this case). I'm using the internal
diodes for rectification and, from what I've read, as long as I don't exceed
the 63 amps they are rated for they should hold up.

Is case that isn't quite clear: varying the voltage to the field coils
varies the output voltage. Normally this is done automatically via the
voltage regulator but the output is limited to about 13.5 volts. This is
not even adequate for charging a 12 volt system. Keep in mind that when you
increase the voltage to the field coils you are also increasing the load on
the engine which can, depending upon many factors, actually reduce the
output if you overload the engine so some "futzing around" may be necessary,
no matter how many calculations you might do beforehand.

Between the gear ratio you're using and engine I can certainly see why
you twisting V-belts, BobG's double V belt & pulley or cogged belt &
pulley is a more expensive route, but should replace you desire for a
direct-drive setup and seems like a must, just too much tension for a
single V-belt.

I've been searching for various combinations of belts and pulleys for quite
some time. Some of these parts are elusive and it takes a lot of sitting in
front of the computer to find out what's available and I simply cannot sit
in front of a computer for more than a couple of hours at one time. At this
point it sounds like a double V-velt with 5/8" belts should do the trick.
The main attraction of a direct-drive setup would be less maintenance and
the entire project would be simpler/easier to build because several parts
would be eliminated.

I get your decision on going with parts you have, but do you think
I'll gain anything going with BobG's setup to start with and learn on,
I'm a little more interested in reliability and long-term cost than
initial cost.

I've only read the one thread by BobG and he sounds like he has developed
his preferences through personal experience. I have only used one Delco
alternator so my experience is very limited. I do not know what the
differences are between the Delco and other alternators but apparently there
are advantages to BobG's setup, especially for low-speed applications such
as wind generators. I probably would never have gotten the thing to work if
it was not for the many knowledgeable people on this NG who have helped me
along with this and many other projects. If I was going to do it all over,
starting from scratch, my first choice would be a permanant magnet
alternator and I would be in favor of a direct-drive setup. With the PMA
you automatically save up to 200 watts of power because you do not need to
excite the field and waste energy making unneeded heat. Another thing to
consider is do you need to make 90+ amps? I only need about 66 maximum.
You might be burning up more fuel to provide extra power that you are not
going to be using. How big is your battery bank?

And yes, it's better to spend more money upfront and build something right
than to waste money with inadequate designs that need to be redone. But we
must also consider replacement costs and repairs. If it can be done with
cheaper parts without making compromises and those parts are easier to get
then I'd lean in that direction. I would not want to get myself into a
situation where I suddenly need an new alternator and it'll take three weeks
and hundreds of dollars to get one whereas another design might be quicker,
easier, and cheaper to replace.

 

[Curbie]

Ulysses,

If I remember correctly, rheostats where used as light dimmer knobs on
old cars, maybe you'll run into one sometime?

Thanks for all your time and help!

Curbie
OtherPower's PMA battery charger
http://www.otherpower.com/steamengine.shtml

 

[Curbie]

Jim,

Rheostats that will handle 3 to 5 Amp field current aren't cheap or
easy to find surplus.

Thanks for the correction, didn't mean to lead anyone astray.

Curbie

 

[[email protected]]

The Nichrome wire should be long enough so you can connect one end to
the field and using an alligator clip connected to the positive on the
alt allows you to fine tune the field by sliding the alligator clip
along the Nichrome.

Why are you pretending to give lessons to Ulysses, or anyone? While
you've struggled mightily without success to explain how much
resistance is required for alternator field-control, Ulysses did it in
one post.

I then found a rheostat on an old spot welder
going for scrap.

<chuckle> In case there are any newbies reading, here are a few of
ghinius ghio's previous rheostat fable versions:

"On the front of this rhostat it is clearly marked "150 Amps". Its
resistance is too low"

Great choice. <snorf> What's the point of having a "rhostat" if its
resistance is "too low"?

"The item in question is a 150 ohm rheostat"

I thought you said the resistance is too low? Field control only
requires a few ohms, so how can 150 be "too low"? You seem, ah,
confused.

"Rheo - 8.5 ohm ceramic"

This rheostat must be suffering from schizophrenia!

"It also rated 150 Ohms. but the 200 Amp rating is intresting"

Oops, the infamous "intresting" rheostat is back to 150 Ohms again,
and the "Amp rating" has changed as well!

"Rheostat 150 Amp 150 Ohms"

Amazing! Maybe it's time for you to add some more "clarification" to
this rheostat's description.

When Rimmer (aka wayne) sticks his nose in you can safely disregard
anything he says.

Even if he quotes you? Too funny. Why not stop prompting the posting
of your rheostat wisdumb, and thereby prevent new arrivals from
learning that you're a quack?



Back to the topic at hand: here's a good article
http://www.homepower.com/files/webextras/mark8.pdf describing the
basics of how to build engine-driven backup chargers, including simple
nichrome-wire field control of alternators.

Here are some photos of my own setup (24V, 2kW)

http://www.citlink.net/~wmbjk/images/genny.jpg Enclosed generator with
aux cooling and external muffler. I re-worked the top cover since that
photo, it's now sloped and lower-profile.

http://www.citlink.net/~wmbjk/images/generator frame.jpg With cover
removed, showing $5 alternator, home made external HD diode-bridge,
and fuel tank.

http://www.citlink.net/~wmbjk/images/generatorcontrolpanelopen2.jpg
Indoor control panel, which started simple and morphed over the years
with addition of mostly surplus bits to streamline operation.
Shows PWM field control unit, auto sequence timers for warm up and
cool down, and throttle/choke

http://www.citlink.net/~wmbjk/images/generatorcontrolpanelclosed2.jpg
Control panel closed. Operation and instructions are simple enough for
a house-sitter


Wayne

attn searchbots: george ghio Renegade writing (sic) bealiba
http://www.citlink.net/~wmbjk/tbfduwisdumb.htm