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


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Old 08-04-2011, 09:27 PM   #1
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Charging deep cycle batt. with car alternator - Do I need a charge controller???

Hi guys,

I'm about to modify my car/trailer so I can charge my deep cycle battery while driving.

So far I have everything I need (battery isolator, breaker, 7-way connector, etc.) but now I have one big question:

Do I need a charge controller somewhere in the system?

I read in many posts and on other websites that deep cycle batteries need to be charged in a special way, i.e. full charge first, then when at 80%, slower charge, then at 90-95%, a slow trickle up to 100%. They even sell specialized chargers for them, and the salesman told me not to charge it with a standard car charger. But my car alternator, which I suppose must be designed to charge a standard car battery (i.e. full power), certainly does not output the electricity in that "special" controlled way.

Will I overcharge my deep cycle battery, or maybe will I charge it in a "bad" way so in the long run will make it less efficient, or go bad after only 2-3 years of use
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Old 08-04-2011, 09:50 PM   #2
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Originally Posted by Roo-lot View Post
Hi guys,

I'm about to modify my car/trailer so I can charge my deep cycle battery while driving.

So far I have everything I need (battery isolator, breaker, 7-way connector, etc.) but now I have one big question:

Do I need a charge controller somewhere in the system?

I read in many posts and on other websites that deep cycle batteries need to be charged in a special way, i.e. full charge first, then when at 80%, slower charge, then at 90-95%, a slow trickle up to 100%. They even sell specialized chargers for them, and the salesman told me not to charge it with a standard car charger. But my car alternator, which I suppose must be designed to charge a standard car battery (i.e. full power), certainly does not output the electricity in that "special" controlled way.

Will I overcharge my deep cycle battery, or maybe will I charge it in a "bad" way so in the long run will make it less efficient, or go bad after only 2-3 years of use
Good news ...NOPE!
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Old 08-05-2011, 12:48 AM   #3
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Car alternator is not the healthiest for a deep cycle battery. It will constantly over charge it. But that is only when your driving. I put a switch on mine so I can turn it on and off. If you're camping a couple days and driving only a few hours, it will work fine. Deep cycles are designed and work way differently than car batteries. And all those things are true. But Truck campers and rvs have ben setup that way since the dawn of time. It's like eating a Mc Donalds everyday. It may not be quite as healthy of recharge, and it will take some time out of my life expectancy. But it works.... Just don't eat all 4 meals there and you'll probably live a average life!

Charge on the go as needed. And when you have power use a trickle charger designed for marine/rv battery.
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Old 08-05-2011, 07:08 AM   #4
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Deep Cycle Batteries

David's advice is sound. We have a set of deep cycle batteries in our motorhome that are now 14 years old. We keep them on a smart converter continuously and regularly check the water level. However when we're driving down the road, the motorhomes alternator charges the batteries.

As to car charging, we also have a switch in series with the charge line to the trailer. This is a perfect battery isolator. We only turn the switch on once the tow vehicle is underway and shut it off before we stop. Our switch has a built in blue LED and stands out when on.

Basically the tow vehicle is not our primary charging method but a solid secondary method.

Norm
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Old 08-07-2011, 12:13 PM   #5
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Alright, this is reassuring.

Although, being a perfectionist, I would like to protect my 200$ battery as much as I can, and that includes charging it the way it was designed to, for the majority of the time, even while driving.

Would a solar controller do the job (even though I have no solar panel)? Are solar panel controllers designed to handle the electricity coming from a car alternator instead of a solar panel? (i mean, 12vdc is 12vdc, wether it comes from an alternator or a solar panel, right?). This way, when i invest in a solar system in a few years, i'll already have my controller installed....

Your advice is greatly appreciated, thanks.
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Old 08-07-2011, 12:42 PM   #6
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David and or Norm;
Could you explain why you think a car alternator will harm a deep cycle battery?
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Old 08-07-2011, 12:53 PM   #7
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For my part, i can only base my interpretation on the fact that the salesman at the store told me i should not charge a deep cycle battery with a standard battery charger. And, there are chargers specifically designed for them. The electricity needs to be "controlled" in some way. That really is all I know.

And since there is a standard battery in my car, i can only assume that my car alternator is designed to behave like a standard battery charger...
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Old 08-07-2011, 01:05 PM   #8
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Originally Posted by Roo-lot View Post
For my part, i can only base my interpretation on the fact that the salesman at the store told me i should not charge a deep cycle battery with a standard battery charger. And, there are chargers specifically designed for them. The electricity needs to be "controlled" in some way. That really is all I know.

And since there is a standard battery in my car, i can only assume that my car alternator is designed to behave like a standard battery charger...
Your alacrity and veracity is refreshing and restorative, Thanks!
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Old 08-07-2011, 03:19 PM   #9
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Tehcnicly should work. But make sure you get one rated for some heavy amps. With solar you are limited to the output of your panels. But I'n this case you will have upwards of 80amps available. If the battery is really low it could try to pull a lot. And Most of those basic controllers I doubt could handle the load. You would want to make sure it is a smart charger. That is the most important thing.
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Old 08-07-2011, 10:24 PM   #10
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I have the 12v line from my TV switched via a relay attached to my parking lights. The relay is located in the camper. This way i can control when the camper battery is being charged via the switch on my dash and can prevent accidently killing my car battery by leaving it on when the engine is off.
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Old 08-08-2011, 06:37 AM   #11
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Battery Charging

Floyd and David,

I did not mean to imply that alternator charging is bad, in our case with the motorhome, the alternator charges the deep cycle batteries whenever we're driving and has done no damage after 14 years with the same batteries. Therefore my conclusion is that alternator charging does no damage.

The significance of the smart charger that our converter provides is the desulfation cycle. Having the batteries on the converter seems to have extended the battery's life. The smart charger on a schedule automatically increases the charge voltage to 14.1 volts for about 15 minutes every desulfation cycle. When ever we're home we leave the motorhome plugged in and similarly for our trailers. It costs little, keeps the batteries charged and provides the desulfation cycle.

I don't know if this extends the life of the typical Marine trailer battery because we haven't had the trailer as long as the motorhome. However I our Deep Cycle batteries are 14 years old. Paralleling that I we power our batteries all year. Is the reason for our batteries life? I don't know but it seems to work for us.

My response in a nut shell. Tow vehicle charging is fine. Maintenance charging when on AC extends life.

By the way our Deep Cycle batteries are Trojan 105s. Also we have a fuse in series with our trailer battery limiting charging current to 15 amps, primarily to protect the wire to the battery. One aspect of continuous charging is that distilled water needs to be added to the batteries at least every six months.

Hope this clarifies my thoughts on battery charging.

Norm
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Old 08-08-2011, 09:15 AM   #12
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Originally Posted by honda03842 View Post
Floyd and David,

I did not mean to imply that alternator charging is bad, in our case with the motorhome, the alternator charges the deep cycle batteries whenever we're driving and has done no damage after 14 years with the same batteries. Therefore my conclusion is that alternator charging does no damage.

The significance of the smart charger that our converter provides is the desulfation cycle. Having the batteries on the converter seems to have extended the battery's life. The smart charger on a schedule automatically increases the charge voltage to 14.1 volts for about 15 minutes every desulfation cycle. When ever we're home we leave the motorhome plugged in and similarly for our trailers. It costs little, keeps the batteries charged and provides the desulfation cycle.

I don't know if this extends the life of the typical Marine trailer battery because we haven't had the trailer as long as the motorhome. However I our Deep Cycle batteries are 14 years old. Paralleling that I we power our batteries all year. Is the reason for our batteries life? I don't know but it seems to work for us.

My response in a nut shell. Tow vehicle charging is fine. Maintenance charging when on AC extends life.

By the way our Deep Cycle batteries are Trojan 105s. Also we have a fuse in series with our trailer battery limiting charging current to 15 amps, primarily to protect the wire to the battery. One aspect of continuous charging is that distilled water needs to be added to the batteries at least every six months.

Hope this clarifies my thoughts on battery charging.

Norm
One important point.... Your 6V Trojan 105's are in a different league than the typical 12V type 24 marine battery used in a small fiberglass trailer. That sort of longevity would be a real reach for the latter.
If you get half that life span from your Walmart "Everlast" type 24 Marine battery, then you are doing something very right.
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Old 09-18-2017, 06:48 PM   #13
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Battery

Not all deep cycle batteries are the same: lead acid types also come in AGM some AGM batteries have no filling area for fluid and less fumes; then they also make a gel cell with no fumes that can be charged indoors.
We decided on a roll pack gel cell m31 to replace the old m27 AGM but the price was $675 no fumes, 61 lbs. it lasts a bit longer price was an ouch!

They are also used in alarm systems indoors only problem is it uses a higher voltage to charge and failed to charge while driving unlike the old AGM lead acid one did.

Have to figure out how to charge it while diving till then have a battery smart charger that will do the job. We only repaired out clearance light wiring durring our rebuild.

What type of battery did you get?
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Old 09-18-2017, 07:50 PM   #14
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...

Would a solar controller do the job (even though I have no solar panel)? Are solar panel controllers designed to handle the electricity coming from a car alternator instead of a solar panel? (i mean, 12vdc is 12vdc, wether it comes from an alternator or a solar panel, right?). This way, when i invest in a solar system in a few years, i'll already have my controller installed.....
What a brilliant idea! I am so glad I thought of it!

But actually, my idea was to feed the converter output (not the tug's alternator output) to the solar controller.

The bottom line of that idea was that feeding the output of the converter to my PWM solar controller was very likely a bad idea. It had to do with how a PWM controller works. I must admit that this might not apply to a tow vehicle but considering the complexity of modern vehicle electronics, I would proceed with extreme caution.

And of course. the 12 volts that you mentioned is not really 12 volts. A "12 volt" solar controller is designed to work with solar panels with voltage up to 19 volts or so. The higher voltage allows the controller to regulate to various lower voltages, including float, bulk charge and desulfurization*, The voltage from a tow vehicle might be around 13.7 at the source, and lower at the trailer. It might or might not be enough for bulk and float charging but likely will not be high enough for desulfurization*. But that only means you don't get a full charge or desulfurization*. It is the effect on the tow vehicle I don't know about and would be most concerned with.
.
.
* Make that desulfation.. sometimes I hate auto-correct.
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