| Re: [GMCnet] Three Batteries and How to Charge Them [message #360886] |
Wed, 16 December 2020 22:55 |
Dave
Messages: 32
Registered: March 2004
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Here are some comments on what I did with our 73 GMC.
At 05:23 PM 16/12/2020, you wrote:
> We have come to the time with this project that we need to update
> the battery storage and charging systems. It is a 73 with one
> battery in the back
> to start the onan. Two batteries in the front. One to start the
> 455 and one to power the house systems.
We moved the house batteries to the rear (under the bed). Upgraded
the wiring. Upgraded the batteries to four 6V golf-cart batteries
(2S2P) 260AH each.
> The original (I'm Guessing on This) isolator
> is in place and I get a click when I flip the power boost switch so
> without a lot of research I am thinking that is normal.
That would be normal. The Boost relay ties the start battery to the
house battery to supply extra current to the starter when/if the
start battery is weak.
> It appears that the two batteries in the front will be charged while
> driving from the engine alternator.
True. The output of the alternator goes into a battery isolator that
will supply equal voltage to both the house battery and the start
battery. The voltage sense for the alternator is on the start battery
side of the isolator. Which can be a problem if one of the diodes in
the battery isolator fails.
> The battery at the Onan is charged by the
> onan when it is running. Having read about how the Onan will fry
> the start battery in time I have disabled that feature and when I
> run the Onan now I
> connect a battery charger (after all when the Onan is running I have
> 120 power) as a temporary fix to keep things going.
If the voltage regulator on the Onan is functioning properly, this
should not be a problem. Given the age of these units this is
something that should be checked.
> I have removed the buzz box
> and selected a converter to replace it that has a smart charge
> feature. When parked the converter should keep the house battery
> charged and provide
> the 12 volt system with power.
Good idea. The buzz box is known to be a poor battery charger. Very
slow to recharge and likely to damage batteries if left powered up
for extended periods of time. When we still had the buzz box we used
a lamp timer to power it up for a few hours each week while in
storage but otherwise left it off unless we were running the electric
fridge and other loads. This never equalizes the cells in the
batteries so it is not a good solution if you want really long
battery life. Modern smart-charge converters solve that problem...
> NOW FOR THE QUESTIONS
>
> If I use the converter to keep the house system battery charged can
> I also use it to charge the Onan start battery while the Onan is running. I am
> thinking that I would have it engaged by a relay that is on the fuel
> pump circuit. When the Onan is on and running there is 12 volts at
> the fuel pump
> and have that activate a relay that connects the positive battery
> post of the onan start battery to the converter charging system using a 10 awg
> should provide ample charging to maintain it.
That would work. But I would suggest using a battery combiner. They
have internal controls that will sense the voltage on both sides and
connect or disconnect the relay as needed without the complication of
connecting to the oil pressure switch.
But a simpler solution would to be to check the charger on the Onan
and fix it if it is not working properly. My experience is that the
charger is one of the more reliable components on the Onan. If it is
overcharging the battery you can probably find a used replacement
from someone for a reasonable price.
I added another battery isolator to the Onan compartment. Connected
the center (alternator) terminal to the front isolator center
(alternator) terminal and one of the other terminals to the Onan
start battery. This will charge the Onan battery whenever the front
engine is started. I have never had a problem with the Onan start
battery going dead. Our last couple Onan start batteries lasted 10
years with this setup.
> My question with this is will it interfere with the charging and
> maintaining of the house 12 volt
> battery?
It will not. Just make sure that you take into account the fact that
the Onan will require a few amps of current to run the ignition
system while the engine is running. If you want to use a separate
smart-charger for the Onan, I would suggest something rated at 10+ amps.
> Next Question
>
> For those of you who have inverters What size do you use and what
> all do you run from them. I am thinking that the only thing I would want an
> inverter to run is the refrigerator and the refrigerator that we
> will be using draws less than 2 amps. My thinking is that
> everything else can be
> left shut down for several hours and have no issues AND maybe this
> is not necessary to do but keeping the refrigerator running while at
> a ball game or
> rodeo and not have the generator running would be preferable. I
> don't mind running the generator 24/7 when we are around the coach
> but I prefer it to
> be shut down when we are not there.
This depends a lot on the type of refrigerator that you are using. We
still have the original Norcold electric. It has an internal 12V
inverter that is very low power and very forgiving. It will easily
run for four days with no charging or indefinably if we run the
generator for four hours a day (two in the morning while cooking and
two in the evening while cooking). All of our loads typically use
~100Ah/day. During dry camping the batteries level out between 50-80%
charge per day. Which is Ok for a few weeks at a time..
If you have a propane refrigerato, and want to run it on electric, it
will consume a lot more power. If it is a 3-way, the 12v draw is much
more than the Norcold. If it is a propane/110v unit then it will be
even less efficient (and draw more current through the inverter).
If you have a 110V compressor refrigerator then the problem is not as
much the power consumption as the surge current. Newer refrigerators
are pretty efficient but some have very high start currents and do
not run well on low cost "modified sine wave" inverters. I have an
office fridge that we use as a second refrigerator for special
occasions and I was not able to get it to run reliably using a 750W
modified sine wave inverter. We installed a low cost Chinese 1500W
sine wave inverter and can run the extra fridge, toaster, microwave
or coffee maker. Not all at once but good enough for tailgating or
fixing meals during the campground "quiet times".
> I know everyone uses their coach differently but it is MUCH easier
> to change things when they are just words on a piece of paper
> instead of bolted in
> place. I am getting close to putting things in place and different
> ideas and opinions are always helpful.
Just be aware that the OEM wiring is not up to the task of using
higher power converters, inverters, alternators etc. We upgraded all
of the primary 12V wiring (positive cables and added negative return
cables) using welding wire. Bigger is better (4-6awg) to keep voltage
drops to a minimum. Inverters need short (as in very short) and heavy
gauge cable runs. And dont forget to use appropriate circuit breakers.
We have used the GMC for many things, from extended dry camping in
the heat of summer or the cold of fall to extended full hookup stays
in all seasons. And this setup seems to work really well. We
typically get 10 years out of all of our battery sets. But the key is
to size them properly and be aware of the charge state at all times.
Lead-acid batteries are pretty unforgiving of being overly charged or
discharged but will last a long time if cared for properly...
> TIA
> Melbo
> --
> Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
Dave
Ann Arbor, MI.
73 Sequoia (26'/455/EbH/RwI/ThH/HEI/TBI/160°/3.42/100A/Q55G)
99 Gillig 36' Low Floor Bus (work in progress)
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