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Topic: LD battery isolator and charging? Which battery is being monitored? (Read 7 times) previous topic - next topic
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LD battery isolator and charging? Which battery is being monitored?
Yahoo Message Number: 99545
So the isolator keeps the engine and coach batteries apart at all time, but allows simultaneous charging both using the alternator.
 But the alternator varies the charging voltage and current based on the state of only one battery (engine).  I don't think LD has done anything to change that, so the alternator does NOT monitor the coach battery at all.
 I'm sure I'm missing something, because my 50% depleted coach battery gets charged even when the engine battery is 100% full.
 Help me understand how alternator charging works in this isolator/two battery system.

Thanks,

Sam
Re: LD battery isolator and charging? Which battery is being monito
Reply #1 –
Yahoo Message Number: 99549
Hi Sam, let's give it a try.

First, the alternator never monitors anything, it only generates power, and only then when the output resistance is lower than the voltage it can create.  It doesn't know which battery it is charging.
 So RV's tie their electrical systems (chassis and coach) together with an isolator, which is a big diode.  The power will only run one way, so that if the resistance of the chassis battery gets low (lower battery state of charge), the coach battery cannot provide power to charge it.  Likewise if the coach battery gets some discharge, the chassis battery cannot discharge itself by charging the house battery.

Any of this make sense?  Remember, any electrical power generator automatically sends its load to the item of least resistance.

There are lots of good references on the net, try www.phrannie.org, which has instructions
Re: LD battery isolator and charging? Which battery is being monito
Reply #2 –
Yahoo Message Number: 99553
Quote
So the isolator keeps the engine and coach batteries apart at all time, but allows simultaneous charging both using the alternator.
 But the alternator varies the charging voltage and current based on the state of only one battery (engine).  I don't think LD has done anything to change that, so the alternator does NOT monitor the coach battery at all.
 I'm sure I'm missing something, because my 50% depleted coach battery gets charged even when the engine battery is 100% full.
 Help me understand how alternator charging works in this isolator/two battery system.
With your Delco SI alternator, you are correct in that the chassis battery is monitored for terminal voltage. It is not, however, a 'smart' system. The alternator output current is simply adjusted to maintain a set voltage of about 14.2V at the battery.
 This means the input voltage to the isolator is a 'diode-drop' higher, between about 0.6V to 1V, depending on the current demand of the chassis battery. The output voltage to the coach battery will also be a variable 'diode-drop' below the alternator output, so will depend on both the demand of the coach battery and that of the chassis battery.
Since the current output of the alternator is split between the two systems, the higher the chassis battery state of charge, the more current is available to the coach battery. Actual current flow to it will be high if the battery is in good shape, but discharged, and much less as it approaches full charge.

One problem with a relay to connect the two batteries instead of an isolator occurs if there is a large discrepancy in the state of charge of the two. If the alternator output is insufficient, you will discharge the chassis battery into the coach battery until the alternator can 'catch-up'.

Steve
2004 FL
2013 Honda Fit
Re: LD battery isolator and charging? Which battery is being monito
Reply #3 –
Yahoo Message Number: 99555
Quote
First, the alternator never monitors anything, it only generates power, and only then when the output resistance is lower than the voltage it can create.
Gus, this is true of 'single-wire' alternators. The Delco SI in the older Chevys has a sense wire used to determine its output voltage.
This feature was used in aftermarket gadgets to produce 115VAC from the alternator.

Steve
2004 FL
2013 Honda Fit
Re: LD battery isolator and charging? Which battery is being monito
Reply #4 –
Yahoo Message Number: 99556
"With your Delco SI alternator, you are correct in that the chassis battery is monitored for terminal voltage. It is not, however, a 'smart' system. The alternator output current is simply adjusted to maintain a set voltage of about 14.2V at the battery."

Steve,

Thank you for the explanation.  It makes so much sense now.
 So, LD (and other manufacturers) takes advantage of this 'non-smart' characteristic of the alternator to arrive at a simple working solution.  If I understand it correctly, by design, this 'non-smart' alternator could potentially overcharged both batteries if driven long enough (12 hr+), because regardless of the battery state of charge, the terminal voltage is maintained at ~14.2V which is much higher than 13.xV maintained by trickle chargers.
 You also mentioned people taking advantage of the sense wire to make AC out of the alt.  Can you elaborate on that, or point me in the right direction so I can learn more about it?  Not planning to do anything with it at this moment, just curious.

Thanks,

Sam

PS:  Thanks too, for the reply to my furnace question.
Batteries and Other Electrical Stuffs (phrannies.org)
Reply #5 –
Yahoo Message Number: 99558
Quote from: Gus Weber"

"There are lots of good references on the net, try www.phrannie.org, which has instructions in all aspects of RVing.

Thanks for wanting to learn"

Hell Gus,
 Thanks for the link.  Do you know when those documents were written? One thing in it seems really outdated (or at least not corresponding to my observation.)  Voltage of batteries at rest:

According to the doc, 12.60 to 12.75V at rest is 100% charged for standard (flooded lead-acid) batteries.

The 2 years old Walmart Everstart Maxx 75S battery for my LD engine always read 13.10 or higher in the morning, after at least 8 hours rest.

My smaller 3 years old battery is my Honda Civic still reads 12.90V in the morning.
 My new $80 Everstart Maxx group 29 (125AH, marine, deep cycle) reads 13.00 when fully charged and fully rested.

I'm looking for a table that tells me (somewhat accurately) when my battery is at 50% charged, so I can either charge or stop using the battery.  I just can't use his table since the initial value is already out of sync with mine.

Sam
Re: LD battery isolator and charging? Which battery is being monito
Reply #6 –
Yahoo Message Number: 99559
Quote
solution.  If I understand it correctly, by design, this 'non-smart' alternator could potentially overcharged both batteries if driven long enough (12 hr+), because regardless of the battery state of charge, the
Not a big issue - 12hr at 14.2V won't evaporate much electrolyte, and 12hr driving at a time is a pretty unusual marathon situation! We've driven as much as 500+ miles at a stretch, but this is with a break or two, over 8 - 9 hrs max. Then we'll stay at least overnight, usually without hookups.

Quote
you also mentioned people taking advantage of the sense wire to make AC out of the alt.  Can you elaborate on that, or point me in the right direction so I can learn more about it?  Not planning to do anything with it at this moment, just curious.
You could do a search, but since most current alternators are incompatible, and inverters cheap, most likely sources would be off-road or emergency vehicle supply - or check back issues of Mechanix Illustrated (50's - 70's) for ads.

Steve
2004 FL
2013 Honda Fit
Re: Batteries and Other Electrical Stuffs (phrannies.org)
Reply #7 –
Yahoo Message Number: 99561
Quote
According to the doc, 12.60 to 12.75V at rest is 100% charged for standard (flooded lead-acid) batteries.
This sounds about right

Quote
I'm looking for a table that tells me (somewhat accurately) when my battery is at 50% charged, so I can either charge or stop using the battery.  I just can't use his table since the initial value is already out of sync with mine.
Sam, battery voltage will depend on state-of-charge and temperature, but 13.0V or higher at rest is wrong for any lead-acid chemistry battery with 6 cells of 2V. I would suspect your meter, unless there is a undocumented charging source hooked up (solar panel?).

Steve
2004 FL
2013 Honda Fit
Re: Batteries and Other Electrical Stuffs- sidebar...
Reply #8 –
Yahoo Message Number: 99563
Sam, to check your meter, I just measured a AA Kirkland brand alkaline cell, brand new in the package, at 65F in our house:

1.604V

using my Fluke 77 DVM.

Steve
2004 FL
2013 Honda Fit
 
Re: Batteries and Other Electrical Stuffs (phrannies.org)
Reply #9 –
Yahoo Message Number: 99564
Quote
Sam, battery voltage will depend on state-of-charge and temperature, but 13.0V or higher at rest is wrong for any lead-acid chemistry battery with 6 cells of 2V. I would suspect your meter, unless there is a undocumented charging source hooked up (solar panel?).

Steve
No, there is no charging source (I have no solar panel).  Even my car (Honda Civic) 3 years old battery reads 12.90 in the morning.  Is 8 hours long enough for a battery to arrive at "rest" state?
 My meter is a regular digital multimeter, GE2524.  It has been faithful to me for years.  But I will try another meter.

Thanks,

Sam