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DC generator vs DC Converter

J

JoeSixPack

Jan 1, 1970
0
Charging 4 T-105s that run a 2000W Go-Power puresine inverter. What's the
efficiency of using an AC generator to charge the batteries through the 12V
converter vs. using some sort of gasoline-powered DC generator, such as a
gas engine-driven automotive alternator? How much efficiency do you lose by
using the AC? The converter is all solid state 45 amp, regulated, and has a
15 amp breaker behind the battery-charging circuit. All equipment is less
than 2 years old.
 
S

Steve Spence

Jan 1, 1970
0
JoeSixPack said:
Charging 4 T-105s that run a 2000W Go-Power puresine inverter. What's the
efficiency of using an AC generator to charge the batteries through the 12V
converter vs. using some sort of gasoline-powered DC generator, such as a
gas engine-driven automotive alternator? How much efficiency do you lose by
using the AC? The converter is all solid state 45 amp, regulated, and has a
15 amp breaker behind the battery-charging circuit. All equipment is less
than 2 years old.
The "converter" may not have the 3 stages necessary for good battery
health. Most dc chargers don't either.

for dc charging you need something similar to:

http://www.amplepower.com/products/sarv3/index.html

for ac charging you need something similar to:

http://tinyurl.com/9jskw

either will do a good job. if you have some non-inverter ac loads, an ac
charger will be a better bet. if everything you have can run on the
inverter, then dc is a good deal.
 
S

Steve Spence

Jan 1, 1970
0
Ulysses said:
As Steve Spence pointed out the converter will not do a good job of charging
your batteries. I also suspect it will go well over 14.5 volts when the
batteries are fully charged.

I am charging four 220 Ah batteries using a Honda eu2000 generator and a
Vector 40 amp Smart Charger. The charger is fully regulated and 3-stage.
If you try to use an alternator to directly charge your
batteries it will be difficult to regulate the current and voltage. With my
Vector charger I don't have to worry about them and they will likely last
much longer than with other types of battery chargers.
I forgot to mention that I have 6 T105's powering a AC Delco 2500 watt
inverter. I use a schumacher 40amp 3 stage charger from Walmart, very
similar to the Vector. This system powers my house.
 
R

Rob

Jan 1, 1970
0
If
you try to use an alternator to directly charge your batteries it will
be difficult to regulate the current and voltage. With my Vector
charger I don't have to worry about them and they will likely last
much longer than with other types of battery chargers.

I'm still trying to figure this all out. I have an almost identical 4hp
engine driving an 80 amp alt, charging two t605's while the batts run a
msw inverter. My thoughts were that the internal regulater of the alt
would handle the current and voltage regulation. I see the extra benifits
of running an inverter to charger to batt set up, but the third stage of
battery charging is a long slow process (correct me if I'm wrong) and as
such, a fairly fuel consuming process on a gas generator. Would it not be
more economical to use the 12v generator to charge the batts up to say 80%
(bulk charge)then let them run down to say 50% before recharging?

I relize the importance of topping up the batts to 100% (between uses) I'm
refering to my not too often power outages. It seems to me that putting
all 80(?) amps for a while into the batts, then shutting down when the amps
drop to 2 or 3 would work? (BTW with a 4" pully on the engine, its not too
far off idle to put out 65 amps (65amps best I ever got )).

I do hook up to a 3 stage charger when the grid returns.

Rob..........
 
G

George Ghio

Jan 1, 1970
0
Steve said:
I forgot to mention that I have 6 T105's powering a AC Delco 2500 watt
inverter. I use a schumacher 40amp 3 stage charger from Walmart, very
similar to the Vector. This system powers my house.
He also forgot to mention the bloody great diesel generator. Steve is
being a bit misleading here.

If you have a charger and a generator use it.

If you use a motor/alternator combination you have two choices;

1) A good charge regulator to control it or

2) Learn to control it manually.

As an aside the T105's are not a great choice for the job.
 
V

Vaughn

Jan 1, 1970
0
George Ghio said:
If you use a motor/alternator combination you have two choices;

1) A good charge regulator to control it

westmarine.com will be happy to sell you a variety of three stage
regulators for alternators. Be prepared to spend about $200.00.

Vaughn
 
J

JoeSixPack

Jan 1, 1970
0
It's been holding battery voltage very steady at 13.8 for several weeks now.
I hope this converter will maintain the batteries in good condition until
they go back into service with the PV array in the spring.

At that time, I'm undecided whether to invest in a quiet inverter-generator
to run for long periods to supplement the P.V. array, or to get an
gas-engine driven alternator to charge them more quickly for shorter
periods. I could live with 75% overall efficiency running an AC generator
thru a converter to charge the batteries, but if it's lower than that, I'd
look more seriously at running a gas powered alternator to charge the
batteries directly.


What's wrong with the internal regulator in the alternator? It seems to keep
car batteries well-charged for years at a time.
I forgot to mention that I have 6 T105's powering a AC Delco 2500 watt
inverter. I use a schumacher 40amp 3 stage charger from Walmart, very
similar to the Vector. This system powers my house.

I also have the option of plugging in a solid state battery charger which
has a setting for deep-cycle batteries. I don't see the need to use it, as
I have no reason to believe it would do a better job than the converter is
already doing.
 
J

JoeSixPack

Jan 1, 1970
0
wmbjk said:
A Home Power Magazine article on the subject. Read the paragraph
that's 7th from the bottom.

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=001BAG

Wayne


I pasted the paragraph in question for your convenience:
Car Voltage Regulators Car voltage regulators will not work well in deep
cycle applications. The regulator makes its decisions based only on the
systems voltage. This is fine with the average car battery which is cycled
to less than 1% of its capacity before being refilled. However, the deep
cycle battery is almost empty when it is recharged. The car voltage
regulator attempts to instantly bring the systems voltage to 1415 Volts. A
12 Volt deep cycle lead-acid battery will not reach a voltage of 14 Volts
until it is almost filled. The net result is that the car regulator dumps
the entire output of the alternator into the batteries until they are full.
This is almost always too much energy too fast for a fully discharged
battery. To compound the problem, the car regulators voltage limit is set
too low for deep cycle service. This low voltage limit means that the
batteries are charged too slowly when they are almost full, resulting in
many extra hours of generator operation to totally fill the battery pack.
Since the car regulator is set at about 14 Volts, we are unable to raise the
system voltage up to over 16 Volts for the essential equalizing charges.

None of those concerns are mine for this application. My intention is to
supplement the charging of the photovoltaics when they can't keep up. This
will mostly happen towards the end of summer before I go on the grid for the
winter. When I run the generator, the batteries will probably start at about
75%, and I want to bring them up to about 95% fairly quickly. A 30-60 amp
charge for a few hours from an alternator shouldn't damage four 225AH
deepcycle batteries, I should think. From there, the photovoltaics can bring
them up to full charge during the day with a 5-15A regulated charge rate. I
am trying to decide whether I need to use an regular AC generator (+solid
state charger) or an automotive alternator for this purpose.
 
R

RF Dude

Jan 1, 1970
0
Why do you need a generator if you have grid? Sounds like the 3-stage AC
charger is for you.

An AC switch regulated charger efficiency is 87% or better. But your gas
engine is terrible. I was just looking at the input BTU/hr numbers for home
standby gennies (~11 kW) and noticed they are about 17% (full load)
efficient when compared to the input BTU required.
 
J

JoeSixPack

Jan 1, 1970
0
RF Dude said:
Why do you need a generator if you have grid? Sounds like the 3-stage AC
charger is for you.

I go off the grid in the summer. At these northern latitudes, the solar
energy is about 10X greater in June than it is in December. Solar energy
becomes irrelevent about the end of August, and some other power source is
needed.

I tried the 3-stage charger, and it worked well, but the 115-12V converter
seems to be holding the batteries at a constant 13.8 V, and until someone
convinces me there's a better way, I can leave it at that.

An AC switch regulated charger efficiency is 87% or better. But your gas
engine is terrible. I was just looking at the input BTU/hr numbers for
home standby gennies (~11 kW) and noticed they are about 17% (full load)
efficient when compared to the input BTU required.


The efficiency is a concern between the two types of gasoline-powered
chargers. That's my only option in the summer whan I'm off-grid. I don't
want to invest in a gas engine powered alternator if the efficiency of going
from an AC generator thru a charger is nearly as good.
 
J

JoeSixPack

Jan 1, 1970
0
Solar Flare said:
Engine driven automobile alternators are usually 3 or more phases and the
ripple
from fullwave rectified 3 phase is next to nothing.

I don't want to float the battery, I just want a quick charge. The
photovoltaics do the final charge.
 
R

RF Dude

Jan 1, 1970
0
Concern for efficiency ($ per kW) would keep you on the grid! ;-))

Diesels are more efficient converting fuel to energy. Add some wind
generators if you can. They will compensate when the sun isn't shining. If
you get some surplus Programmable Logic Controllers, you can set yourself up
with a "Cycle Charged" energy approach as used in many isolated
communications sites (helicopter access). Without getting specific, I can
tell you there are cycle charged sites in Canada using wind and solar where
the generator rarely ever has to start up. Wind and sun provide all needs
with the rare top up by generator. To make this work, a very large battery
is required so that you can go a few days without worring about low output
from wind or sun. The PLC can shed load if necessary, or convert excess
load to other useful purposes. It can tweak the charge regime to make sure
all resources are running at full efficiency. For instance, the generator
is never used to fully charge the battery... not efficient. But excess
energy from sun or wind can bring the battery to 100%. Etc.

Your 13.8V should be OK for float. You won't get the battery to 100%
efficiently with a generator / charger set to this voltage. Battery float
charging is an exponential curve. It may take a battery a few hours to get
to 90%, but a week to get to 100% capacity on float voltage alone. Not
acceptable for engine charging systems. Thus engines are used to get the
battery to ~90% only. The smart chargers change this scenario somewhat, as
you can keep flowing energy into the battery closer to the desired 100% by
raising the voltage (to 14.4 say). But the trick is to back it off to safe
float voltage before damage (or gassing) results.

RF Dude
 
J

JoeSixPack

Jan 1, 1970
0
Because of the heating effect?


How much is too much?

Nick

That's a bit confusing, because it's my understanding that a storage battery
does a fine job of leveling off the peaks and troughs in any circuit
connected to it.
 
G

George Ghio

Jan 1, 1970
0
JoeSixPack said:
That's a bit confusing, because it's my understanding that a storage battery
does a fine job of leveling off the peaks and troughs in any circuit
connected to it.

The danger here is just too much bad advice. Now from your post:

"None of those concerns are mine for this application. My intention is
to supplement the charging of the photovoltaics when they can't keep up."

You can do this. You will need a regulator to control the charge.

You have three choices:

1) The reg built into the alt. Only if you are desperate.

2) A purpose built reg. Better control, better charging.

3) The reg you have between your ears. Works well, runs on full logic
but requires you to stay awake.

I believe you said 4 225Ah batteries. If that is in fact 500Ah all up (4
T105s series/parallel) then a 30 amp alt will be fine, 60A would be
pushing the friendship a bit. C10 would be 50A. But you want to bring
your batteries up faster than ten hours.This means you need a charging
regime to suit your needs.

My charger:

5hp motor, 35A Bosch alt(external reg type, reg not used) Rheostat for
field control. This is the famous 150A rated ceramic Rheostat scrounged
from a spot welder.

Take the state of charge in your batteries. Yes it is important that you
not let them remain at a low state of charge for long periods, on the
other hand they do not need to reach 100% charge every single day
either. I will run the little generator to charge my batteries if they
drop to 12 Volts (but like the fine print says ”Conditions Apply”)

Condition: Batteries read 12 volts at four o’clock in the afternoon

Condition: I know the sun won’t be out tomorrow.

Condition: I need to use the computer for several hours that night.
(This condition has been negated due to better computer.)

Condition: There will be three hours of Red Dwarf on TV that night.

It takes at least two of these conditions to warrant the running of the
generator. It may be that your "required" conditions will be different.

And when it comes to charging the batteries I am not trying to bring
them up to 100%. I am doing what I call ”Maintenance Charging” which is
to say that I only require that they be in the top twenty per cent of
their capacity. The sun usually does the rest.

When required I run the gen for less three hours. This is for a battery
set of 840Ah. During winter this may be as much as 3 hours a week or as
little as 1-2 hours/month.

Will this harm your batteries, only if you're stupid and don't pay
attention to what you are doing.

Oh, I also run a logger on my system so I know what is going on, at all
times.

George
 
B

Bruce in Alaska

Jan 1, 1970
0
snipped for brevity

Where I'm going is the idea of a system where an engine/alternator
operates for the peak 2 to 4 hours per day, also supplying hot water
and heat as co-gen, but then the battery/inverter system coasts the
lighting and less energy intensive appliances through the rest of the
day - but (and this is the big but) the system can operate in this
mode indefinitely.

Is something like this feasible?

This is basically how I use my system. I have twin 20Kw Gensets
that I run for a totall of 10 hours a day. (7Am to noon, and 5Pm to 10Pm)
That takes care of the main High Power Loadings of Breakfast and Dinner
and the charging of all the battery banks for the twin inverter systems
connected. It also keeps the four freezers at better than -10F on a
24/7 basis, and the telco equipment battery bank charged. I have had
really good luck with both a 1200Amp/hour 24Vdc L16HD bank, as well
as a 800Amp/hour 24Vdc Absolyte II AGM battery bank. These are on
the inverter systems. L16 bank is over 4 years old, and replaced a
800Amp/hour bank that was 12 years old. The Absolyte II bank is 8 years
old now and still has 95% of the new capacity.

Bruce in alaska
 
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