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House batteries and voltage charge rates
A while back some of you will remember I had 8 8D batteries that were shot after less than one year and Apex sent me 8 new ones. I have a 1995 Prevost Country Coach. The instructions for the batteries state that the bulk charging should be at least 14.6 volts at 70 degrees. I have found that shore power will enable the charge voltagle to reach 14.6, but when running the generator, the bulk charge will only reach 14 volts. The main alternator from the motor charges at 13.8. I have it plugged into shore power at home, but generally when we are gone, I am rarely if ever plugged in to shore power; it is almost always the generator. We are gone often for days or weeks with the batteries only being charged with the generator. Maybe this is the reason the batteries did not last? What can be done so the generator can also bulk charge the batteries up to 14.6 volts?
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14 Replies
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When you run your generator or are on shore power the charging current is coming through the inverters so the answer to the question has to be to find out what is different?
Is your generator voltage and shore power voltage at 120V (plus or minus the allowable 10% utilities are allowed)?
What kind of inverters do you have and are you sure of the charging voltages? Are you applying different DC loads when you are on shore power versus generator power? In other words when home on shore power you may not have the tivoli lights on, but while you travel you may use them a lot and they are a faily large current draw from batteries.
Something is different and that might be the answer.
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If you’re relying on auto-start and that sounds like what you’re saying, the inverter settings could have different values. Gen power and shore power as relates to input voltage should be the same or at least close.
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As an experiment, I let the batteries discharge about 20’%, then l turn off all of the DC loads in the coach. i then start the generator and test the voltage coming off the terminals of the inverters, Xantrax, freedom 2500. After testing, I turn off the generator and plug it into shore power and again test the voltage at the terminal post. Again, there is no DC load. The voltages are different.
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Have you checked the input AC voltages to the inverters? Are they different?
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See first post…..are the shore and generator power the same and within the allowable range of 10% variation?
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I just checked the incoming power from the generator and then shore power; they are nearly identical. Both are 120 to 121.
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With identical incoming power to the inverters you said the output voltage varies depending on if it is generator or shore power?
It is like the inverters know the power source. They don’t.
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I understand exactly what you are saying, but I can add that my voltage meter also does not know what power source is on and it gives me a different number depending on if it’s the generator or the shore power. If .5 volts really won’t make a difference for the batteries, I’ll just let it go. I’ve just read a lot of posts stating that following the voltage recommendations is vital for optimal battery life.
I appreciate all the feedback and am very glad this forum exists!
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Tom can add to this because he is far more qualified to discuss batteries, but your battery manufacturer has a charging protocol that will provide you with the greatest battery performance and life.
The charging current in bulk that we typically see is (14.2 or 28.4), similar for absorb and somewhere around 13.6 for float. I hedged my words because those are not absolutes and are influenced by temperature. Later model inverters have temperature sensors, and will adjust charging current accordingly.
Yet on most of our coaches that charge both house and chassis batteries from a single alternator are set for a max charge voltage of about 27.7. Obviously if that is the sole charging source such as for chassis batteries it is less than most charging voltages that are required, but despite that our batteries provide good service, mine being 5 years at which point, regardless of condition they are replaced. That charging voltage however is a safe one because if the chassis bateries are warm the lower voltage is within safe limits.
I have no clue why your inverter battery charging voltages are varied due to the source of power. but there is something different that has not yet been identified.
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It could be something as simple as a transfer contractor beginning to fail.
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I would agree Jack except he has indicated identical voltage readings for AC power, yet a deviation of DC output on the charging side.
If the input power to my inverters has been within an allowable range, up or down the charging current has always been constant.
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I just spoke with the technical department of Xantrex inverters. The man I spoke with was very helpful and knowledgeable. I certainly cannot tell you what he explained to me because it was much too technical for me to understand. My version: the incoming voltage from the shore power and generator may be identical, but it is not identical. He talked of variances of hertz and more importantly the “waves”. The shore power will most likely be ideal, but the generator power will not be especialy with the age of the generator. The regulator or something with the generator would have to be adjusted if I want the outgoing power to be identical.
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So the 120V from the generator is old electric, not to be confused with the new electric from shore power?
Silly gauges and measuring instruments. You would think they would show the real voltage values.
Why is it when a company is called regarding a problem it is always’s somebody else’s equipment that is the cause of the problem? Perhaps the more astute electrical people on the forum can tell me why when eric says both the generator and shore power are showing around 120V that one is an accurate voltage and the other isn’t because the generator is old.
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We have a bunch of EE’s on the forum, let’s hear what they have to say.
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