Some power/battery questions (charging, maintenance)

[padlin]

nice writeup Jon.

[cpaharley2008]

Greg,
If you have the inverter option, you should turn it off, if not using it. The reason being is it is still drawing battery power while "on" and in "standby" mode. So to prevent battery drain turn the inverter off and also your main toggle switch off, after you straighten out your 12v light issues.

[debedb]

If you could get one to run off it's own internal battery you'd sort of invented perpetual motion.

Not really -- I didn't mean that the maintainer runs off the converter (that would indeed be a problem with the second law of thermodynamics ). I meant that the maintainer has been plugged in to a landline power separately from the trailer -- it's just that I don't know if it actually needs to continue to be plugged in to do the maintaining/trickle charging (then there's no point). But if it can store charge in its own battery and then that can be used to trickle charge trailer batteries -- that is essentially just an extra backup battery (for when it's raining, so no solar, and the power is out).

[rubicon327]

Originally Posted by debedb

rubicon, thanks

FYI I edited my post to include some portable solar options for you to consider in case you didn’t see it.

[GeorgiaBill]

When the battery is being charged from the tow vehicle, what prevents an overcharge?

Does the current flow thru the converter? or maybe the alternator prevents overcharge?

[jxoco]

Originally Posted by GeorgiaBill

When the battery is being charged from the tow vehicle, what prevents an overcharge?

Does the current flow thru the converter? or maybe the alternator prevents overcharge?

Yes the tow vehicle alternator and the resistance of the wire from the alternator to the trailer battery are the things that control the voltage that gets to the trailer battery from the tow vehicle.
The alternator is usually around 13.6v and you usually lose thru the cables, down to 13.2 - 13.4 at the battery in the trailer.
It does not go thru the convertor.

[cpaharley2008]

The same thing that prevents your alternator from over charging your car battery.....a relay or something that stops the flow once the battery is charged.

[Brian B-P]

Originally Posted by cpaharley2008

The same thing that prevents your alternator from over charging your car battery.....a relay or something that stops the flow once the battery is charged.

It's the regulator which controls the alternator field current and thus the alternator output, not just a relay shutting off the connection of the alternator to the rest of the system, but yes...

Originally Posted by GeorgiaBill

When the battery is being charged from the tow vehicle, what prevents an overcharge?
... maybe the alternator prevents overcharge?

the tow vehicle's control of system voltage is what prevents both batteries (tug and trailer) from overcharging.

[Vermilye]

Originally Posted by Brian B-P

It's the regulator which controls the alternator field current and thus the alternator output, not just a relay shutting off the connection of the alternator to the rest of the system, but yes...
the tow vehicle's control of system voltage is what prevents both batteries (tug and trailer) from overcharging.

It is also what keeps the tow vehicle's alternator from doing a good job of charging the trailer battery. Most modern vehicles (trucks with a separate tow package sometimes being the exception) quickly drop the charging voltage/current as soon as possible (to improve gas mileage), which, along with wiring losses, severely limits the voltage from the tow vehicle to the trailer battery.

A practical solution is to add a DC to DC converter in the trailer. Set the output to match the absorption voltage of your battery, and you are much more likely to end up with a charged battery after a drive.

[Brian B-P]

Originally Posted by Vermilye

It is also what keeps the tow vehicle's alternator from doing a good job of charging the trailer battery. Most modern vehicles (trucks with a separate tow package sometimes being the exception) quickly drop the charging voltage/current as soon as possible (to improve gas mileage), which, along with wiring losses, severely limits the voltage from the tow vehicle to the trailer battery.

A practical solution is to add a DC to DC converter in the trailer. Set the output to match the absorption voltage of your battery, and you are much more likely to end up with a charged battery after a drive.

Absolutely!

The location of the regulator's reference input - at the alternator output or nearer to the vehicle's battery - is also an issue, due to the voltage at the trailer battery being lower due to those wiring losses. If the tow vehicle's charging system was regulating the voltage at the trailer battery - even with the standard logic - trailer battery charging would be better than it is. That's not reasonable (although it could be done with a separate alternator and regulator dedicated to the trailer) so the solution is the DC to DC charger. Of course, it's a solution to an issue which for many trailer owners isn't a big problem.

[debedb]

FYI I edited my post to include some portable solar options for you to consider in case you didn’t see it.

Great thanks!