Charging deep cycle batt. with car alternator - Do I need a charge controller???

[Raspy]

Yeah.

It's all interesting and there is more to it than any of us know. No argument intended.

Working with all the systems, from suspension to charging to water systems to towing, is all about doing it in person and observing what is going on.

It's hard to take opinions and factor them into conclusions that make sense. You can compile a lot of information, but the best thing is to go do it and figure out what does and does not work and why.

Batteries are a good example. They are always inedeguate, non linear, expensive, dangerous and weaker than we want. How are they best managed? How do we match our power needs with the equipment we have, etc.

Interesting? Yes.

[Buggeee]

The easiest thing to manage with our battery systems is our expectations. A little adjustment on that here or there makes a huge difference in how they perform for us. When I lowered my expectation to have my battery bank last forever I started enjoying the adventure with it a lot more. Tow vehicle, solar or various kinds of converters all have limitations in how they manage the degradation of the lead plates. Do nothing, and they will degrade anyway. The bank is ultimately an expendable. Like firewood I guess, but in very slow motion. Enjoy it while it's there, have a marshmallow, and plan to gather more wood, um, I mean cells, when it's no longer putting out the electrons like it used to.

[fofobraselio]

I'm planning to install this device called a TBCM-40A that I will be using to float charge the trailer battery.
I will never expect this charger to fully charge a battery from empty but will consider it a useful tool for topping it up while driving along.
More details here http://www.atkinsonelectronics.com/m...s/TBCM-40A.asp

[Buggeee]

Originally Posted by fofobraselio

I'm planning to install this device called a TBCM-40A that I will be using to float charge the trailer battery.
I will never expect this charger to fully charge a battery from empty but will consider it a useful tool for topping it up while driving along.
More details here Atkinson Electronics Inc - TBCM-40 TRAILER BATTERY CHARGING MODULE

Looks like a handy relay. It doesn't look like any kind of charger or controller from their description, just a cut off with a relay that flips the connection on when there is a power running from the TV alternator. The TV alternator is the "charger" so to speak. This item seems to prevent the trailer battery from drawing off of the TV battery when the alternator is not providing charge to the system?

I didn't know enough to guard against depleting the TV battery when the TV was not running. I always assumed it shut off the connection when I turned the key off. Ignorance is bliss I guess. Does this problem happen with any TV or just certain categories of TV?

So you know, for the longest time I thought everyone was talking about their television instead of their tow vehicle so there you have it.

[fofobraselio]

Yes, it won't kill your TV battery because it will only take upon power when the TV battery is at 13.5v or higher (alternator is working and TV battery is fully charged) also prevent sulfation by not having a. 75V drop like other isolators. I wonder if it could potentially over charge the trailer battery though?

[Buggeee]

Here's a link to another thread on this topic from a few yars ago

http://www.fiberglassrv.com/forums/f...ery-61497.html

I hesitate to link a thread from a solar charging forum because I don't know if that's allowed.

I offer this next observation as a topic of discussion rather than as a statement because I do not have the knowledge to run through a proof of it -

The consensus in what I'm reading seems to be that, as a practical matter, the voltage and/or amperage drop resulting from the long length and small diameter of the wire leading from the TV alternator all the way back to the RV trailer battery all but eliminates any opportunity for the TV to damage the RV trailer battery by overcharging it. Instead, the risk would be undercharging and sulfation if someone were to rely on the TV as the only life long source for charging. Talk among yourselves

[John Linck]

My TV and 100 watt solar panel both charge a group 27 battery when driving. Works well in keeping the battery fully charged. Still, even after many multi-thousand mile trips there is little drop of the battery's water level so I don't think there is much over-charging going on. I now check the level twice a year and add an ounce or two of RO processed water to each cell once a year.

I suspect the solar controller cuts off the panel when it "sees" the charge coming from the TV, but that is only speculation. Since we never plug in to shore power the combination seems to work well and I seldom have any issues with low charge in our boondocking only camping. The one time I remember dropping below 12.1 volts was while camping under dense tree cover at Yosemite after 5 days with a bit of night time furnace use. We had to tow and park at a sunny meadow for an afternoon of hiking and reading while the solar panel did its thing.

Cheers, john

[Buggeee]

Originally Posted by fofobraselio

I'm planning to install this device called a TBCM-40A ...
More details here Atkinson Electronics Inc - TBCM-40 TRAILER BATTERY CHARGING MODULE

Ordered one of these. Thanks for the link Fofo.

[fofobraselio]

Originally Posted by Buggeee

Ordered one of these. Thanks for the link Fofo.

No problem, don't forget to install a 40A circuit breaker between TV battery and relay. Atkinson also recommends using at least 10G wire between TV battery and the unit.

[Raz]

If your vehicle came factory wired, the relay may already be there. My Frontier disables the charge line when the key is off.

[Raspy]

Originally Posted by Buggeee

The consensus in what I'm reading seems to be that, as a practical matter, the voltage and/or amperage drop resulting from the long length and small diameter of the wire leading from the TV alternator all the way back to the RV trailer battery all but eliminates any opportunity for the TV to damage the RV trailer battery by overcharging it. Instead, the risk would be undercharging and sulfation if someone were to rely on the TV as the only life long source for charging. Talk among yourselves

There is no risk of overcharging a lead acid battery while charging it from the TV and it has nothing to do with wire size. The trailer batteries want to see the same charging scheme as the vehicle battery. The TV also has lead acid batteries and they are always connected to the vehicle charging system. The TV charges them to 14.1 volts all the time while driving. When stopped they rest down to 12.65.

My favorite way to charge the trailer batteries (4 trojan T-105 deep cycle six volt batteries) is to hook up jumper cables to them from the TV. This bypasses the small charging current available from the TV plug and gives them around 150 amps that is regulated to 14.1 volts. It gets the job done and it can't hurt the batteries.

Then, while driving, the TV can supply them with a smaller current through the plug and eventually get them up to 14 volts. When I stop, they are fully charged if I've driven far enough. Then they also rest down to 12.65. Ready for duty.

Charging systems must take lead acid batteries to 14 volts to achieve full charge and avoid sulfation. But that it too high to hold them continuously as it will boil out the water. So, once the battery gets to 14 volts, with a smart charger, the charging voltage is reduced to about 13.2 volts for maintenance. This is still higher than full charge, but won't hurt the battery. A fully charged battery, once rested and ready to go, will register 12.65 volts.

In cars, the voltage is set at about 14.1 volts, but they are not run continuously. The batter sits most of the time not charging. This allows a long battery life without a "smart" charging scheme with a maintenance voltage. Either on at 14.1 or off and resting.

[workhorsed]

Hi, good question and knowing the characteristics of flooded batteries and vehicle alternators will provide some insight to help answer the question.
First the guy that sells you the battery will often tell you whatever it takes to sell you yet another device!!
Batteries are self regulating as the voltage (pressure) goes up so does the back pressure,
A one hundred amp alternator will only make close to that briefly when charging a very low battery. As battery voltage rises the amperage declines.

This is a fairly simplistic overview but it serves to explain what is happening at the battery.

Yes there are chemical differences between starting batteries and real deep cycle units, however the intent is to pack as many watt/hours as possible into those deep cyclers. The starting battery just needs topping up as your vehicle is really running just on the alternator

So feel free to use the excess output from your alternator, it greatly exceeds your converter output! AND, motor homes do it all the time without harming either their expensive deep cycle coach batteries or their SLI ( starting, lighting, ignition) chassis battery.

Real deep cycle batteries need a fair amount of attention to electrolyte levels and terminal cleanliness. Failure to do this is the most common cause of early failure

You don't need a controller and it is only additional expense and complication

Others here have suggested many ways to make the connection, just be sure to have both a switch and a suitable fuse, jobbers sell a fuse with pigtails.

To prevent arcing make sure that that connection is off before disconnecting the trailer harness. G.