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Old 12-24-2019, 09:53 PM   #1
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2007 19' Bambi
Glen Mills , Pennsylvania
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Charging and Drawing

A bunch of newbie questions, but I thought multiple posts would be worse.

I cannot find any documentation on how my new-to-me 2007 Bambi 19 establishes priority between electrical sources. I also cannot find basic info on a few simple items in the manual. Here are my questions:

1. If you leave the Tow Vehicle connected, under what circumstances (if any) will the AS batteries draw from the vehicle?

2. I see no change in voltage at the AS batteries when connected to Shore power. They are at 12.6V under both circumstances. Is there a trigger voltage for the onboard system to charge, or do I have an issue?

3. Why is the Battery store/use switch a momentary switch ? Why not a regular on/off switch ? What happens if it is accidentally turned on while connected to shore power?

4. When should the refrigerator fan be turned on?
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Old 12-25-2019, 04:20 AM   #2
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I can try to help with some of this. Your tow vehicle question depends on your brand of tow vehicle. Some stay connected all of the time, others only when the ignition is on. First, the safe bet is just unplug your 7-way when you reach your destination, a rest stop won't matter. But if you really want to know, google the connector diagram and use a voltmeter to measure across the ground and 12v connections on your tow vehicle connector. If the ignition is off and you have 12v(GM) then your TV battery is at risk of draining as it charges your trailer batteries connected.
Your batteries will not charge from shore power unless the Store/Use switch is in USE. If you do not see a voltage increase then, there is something wrong with your charger or the supply to it.
A relay for the Store switch gives AS the ability to remotely operate the disconnect and to allow more amperage capability than a simple switch would allow.
Larry
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Old 12-27-2019, 07:46 AM   #3
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Quote:
Originally Posted by lsbrodsky View Post
I can try to help with some of this. Your tow vehicle question depends on your brand of tow vehicle. Some stay connected all of the time, others only when the ignition is on. First, the safe bet is just unplug your 7-way when you reach your destination, a rest stop won't matter. But if you really want to know, google the connector diagram and use a voltmeter to measure across the ground and 12v connections on your tow vehicle connector. If the ignition is off and you have 12v(GM) then your TV battery is at risk of draining as it charges your trailer batteries connected.
Your batteries will not charge from shore power unless the Store/Use switch is in USE. If you do not see a voltage increase then, there is something wrong with your charger or the supply to it.
A relay for the Store switch gives AS the ability to remotely operate the disconnect and to allow more amperage capability than a simple switch would allow.
Larry
Thanks Larry for this helpful info. When Shore power is connected, my Store/Use light is on, so I assumed it was in the right position. I did not think to operate the switch.
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Old 12-27-2019, 07:49 AM   #4
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When connected to Shorepower the switch will be lighted in both positions, as you found out. When not on shorepower, the switch only lights in the ON position.
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Old 12-27-2019, 09:39 AM   #5
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Great info Larry. If you'll indulge me let me add some more details:

1. When connected to the TV and the TV engine is running, the TV alternator will partially charge the AS battery system but will generally not fully charge it even during a long drive. Lots of info on why this is the case. Search for a full explanation.

2. Many older model AS have the Converter connected to the load side of the store/use relay so as Larry indicated, the relay must be pull in to charge the battery. The In Use light will illuminate with shore power because the light is wired to the load side so the converter will supply power to the light and the distribution bus even if the store/use relay's solenoid has not pulled the switch in. As Larry indicated, the trailer circuits will be powered by the converter, but the battery remains disconnected and will not charge.

3. The Store/Use switch uses momentary contacts and a permanent magnet so that the switch stays in last position without consuming any load except when the panel switches are depressed. No issue if it is pulled in (on) while using shore power either before or while connected to shore power. When pulled in, it will connect the converter to the battery and allow the battery receive a charge, as Larry indicated.

4. The refrigerator fan redistributes cool air away from the adsorption coils, and thus improves refrigerator performance, but it uses a bit of power. Use it when you have spare power or are connected to shore power with the batteries in good shape. Try to avoid using it when boon docking and and you are conserving power.
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Old 12-28-2019, 07:53 PM   #6
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Thanks Brian, this is an ongoing testament to the value of being part of this online community. Your response does raise one further question for me though. Why wouldnít I always want shore power to top up or maintain my batteries? In other words, why would it default to not charging my batteries?
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Old 12-29-2019, 04:22 AM   #7
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It does not default to anything, you have to choose. If you are plugged in to shorepower and your switch is ON then the charger will charge your batteries. If the switch is OFF then your batteries are disconnected from the charger and the converter. In older Airstreams people would leave the switch in OFF when connected to shorepower so that the battery did not overcharge. However, your charger in your newer trailer is smarter and that won't be a problem. Uless you are storing your trailer, I would leave the switch ON when connected to shorepower and when using the trailer.
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Old 12-29-2019, 07:54 AM   #8
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Once again, Larry provided a sound explanation but because I'm a bit OCD I'm going to add a couple additional points to consider.

As Larry mentioned, high quality digital converters have generally replaced the older and dumber converters that commonly overcharge batteries. Severe overcharging overheats the battery due to internal resistance and sometimes, not often, caused batteries to explode. Modest overcharging for long periods consumes water, which if not soon replaced, causes cell plate damage. Minor overcharging (0.1 -0.3 amps) is generally not a significant problem tough it does consume a bit of water.

Okay what to do?

Don't use a fixed current charger that does not automatically revert to a trickle charge or cycle off when it detects the battery is charged unless you can be present to turn it off manually within a couple hours.

If you have an older dumber converter/charger, well, isolate it if the battery is charged and not in use for extended periods; say more than a couple days.

Modern chargers are generally pretty good as Larry indicated, but there are ways to improve on them. Since full charge voltage and required charging voltage varies significantly with cell temperature, Converter/Charger controllers with battery temperature compensation are much better than those that lack them when the battery temperature deviates much from 70 degrees. Since the uncompensated chargers generally assume the battery is at room temperature they tend to overcharge cool batteries and can fail to fully charge very cold batteries. If you don't experience cold weather very often it's not a big deal.

Also the best controllers have custom charging profiles to match any particular battery and condition. If you are in love with your battery, that is the way to go. It will love you back. If you get a fancy controller consider isolating your converter as they are on older models. some cheaper converters are not designed to be free of the capacitance/load balancing provided by a battery so check that out first.

Now those of you who are not battery geeks, don't worry too much about all this, just run the trailer the way it was designed, maintain the battery as advised and it will last a fair amount of time. Not as long as if you treated it with kid gloves, but that is the trade off.
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