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Old 08-22-2014, 01:36 PM   #1
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How do house batteries get charged when engine is running?

Does the converter/charger in the house come in to play when the main engine alternator is running? I'm wondering if the main alternator charges the house batteries directly (with it's full 175amps), or does the alternator current flow to the converter/charger, and from there, charge the house batteries with lower amperage?

The reason for my question: I want to add a second battery bank to my 2013 Thor Ace, and I want to connect the two banks with a Yandina battery combiner Yandina Marine Electronics. If the house batteries are exposed to the full 175 amps from the engine alternator, then I should buy their C160 combiner. I have the feeling there isn't near that much current charging the house batteries, so I'd like to get away with buying their 100 amp switch at almost half the price. I guess I could ask them, but they seem to be all about boats, and not so much motorhomes.

What do you think?

--DonK
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Old 08-22-2014, 01:56 PM   #2
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Does the converter/charger in the house come in to play when the main engine alternator is running? I'm wondering if the main alternator charges the house batteries directly
--DonK
DonKarstedt
On most, (if not all), motor homes the ONLY alternator, (which is driven the engine), charges both the chassis and house batteries through the inverter if/when the engine is running.
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Old 08-22-2014, 02:12 PM   #3
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On my older rig, the alt. charges the batts. through an isolator.

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Old 08-22-2014, 03:38 PM   #4
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Thanks. Based on that information, it sounds like I am NOT safe to use their 100A combiner. I'll get the bigger one since I have a 175A alternator on the Ford chassis.

--DonK
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Old 08-22-2014, 04:21 PM   #5
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I have a 160A alternator on my MH. It charges both the house and chassis battery through an isolator similar to the one shown above. There are four 6v Golf Cart house batteries, two 8D starting batteries, and one generator starting battery.
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Old 08-22-2014, 06:32 PM   #6
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We have 160 amp alternator with isolator for coach and chassis.

Another isolator up front for generator battery.

Some isolators are just large diodes whike others are contactors.

Main difference is diode isolators require alternator voltage to be slightly higher by about 0.6 vdc to compensate for diode in series.
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Old 08-22-2014, 07:35 PM   #7
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Your converter or inverter has nothing to do with charging your batteries while you are driving down the road. Your chassis and house batteries are basically tied together and the alternator charges them all while driving. Two types of devices can be used to accomplish this. One is a simple heavy duty relay that connects the 2 systems together. The other is a solid state battery isolator. You don't need to worry about connecting your house batteries to your 175 amp alternator. It will not over charge your house batteries any more than it will over charge the chassis batteries.
Stand by. Arguments will follow.
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Old 08-22-2014, 08:24 PM   #8
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The output from the alternator will be shared by all loads so no need for the large device by that.

But what is the cost difference?

Get the biggest one you can fit if the cost is not much more as it will be built better.

There may be more to think about here regarding distribution unless you are making connection to existeng batteries.
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Old 08-22-2014, 08:28 PM   #9
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I'm wondering why you want the combiner. You already have some kind of isolator to separate the house and chassis batteries. Most folks just parallel the second battery to the first. Unless you plan on splitting the house load or are trying to charge a trolling motor I don't see a need for the Yandina unit. I could see it if you did not already have the isolator in the system. I could also see how it's possible to overload the existing isolator if it is not big enough. You will have that problem anyway.
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Old 08-22-2014, 08:30 PM   #10
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I want to add a second battery bank to my 2013 Thor Ace



--DonK

more background info will help. Why do you want to add another "bank" of batteries, and then isolate them?

You already have starting batteries which are isolated from your "house" batteries. To increase your capacity, just add more batteries. You don't need to isolate them from the other "house" batteries.

If you have two 6 volt batteries in series, you can increase that to four batteries to double your amp hours. If you have one 12 volt battery, you can add one or more additional 12 volt batteries in parallel to double or triple your amp hour capacity.
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Old 08-22-2014, 08:33 PM   #11
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Looks like this device is just a contactor that connects tge second set of batteries.

If you are just adding an additional set of batteries to the coach battery and tgey are the same type and size then they can be connected directly to the existing battery with proper wiring and protection...fuse or breaker if not directly next to the existing battery.
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Old 08-22-2014, 08:39 PM   #12
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DonKarstedt
On most, (if not all), motor homes the ONLY alternator, (which is driven the engine), charges both the chassis and house batteries through the inverter if/when the engine is running.
Mel
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It would be very inefficient to charge batteries by taking the 12 v DC, invert it to 120 v AC, then change again back to 12 v DC. You lose some energy at each change.

Most RVs that charge both banks of batteries from the alternator use a battery isolator. There are many types, some connect as soon as voltage is detected, others delay and allow the chassis battery to recover the energy used in starting before connecting and charging the house batteries. When the alternator is no longer charging because the engine has stopped, the battery isolator disconnects the two battery groups so they are independent and the chassis batteries are saved for chassis duties.

Likewise when the converter/charger or inverter/charger is energized by the shore cord or generator, the current from the charger is sensed by the battery isolator and allows both groups to charge.
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Old 08-22-2014, 09:07 PM   #13
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My original battery bank is 2 twelve volters connected in parallel. I want to increase capacity, and I have convenient space for a third battery. My first inclination, was to simply buy a third battery and connect in parallel with the first two. Sounds easy, but I did some deeper research and found that even though this would work, it's not ideal unless all three batteries are the same exact type, age, and share the same charge history. If I want to heed that advice (I think I do), then I have three choices:

1: get rid of my original two batteries and replace them with 3 matching new ones (wasteful, since the original two still have years of life left)

2: Wait until the originals wear out, then replace with three. (I don't have the patience)

3: Add the third battery, but separate it as "Bank 2" with the Yandina combiner. That way it stays charged with everything else, but it will stay separated in reserve, and allow me to switch to it if I run Bank 1 dry.

My original question and concern was about buying the correct size combiner switch for my alternator--I really wasn't worried about overcharging anything.

Thanks for all the good discussion.

--DonK
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Old 08-22-2014, 09:32 PM   #14
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That is a good idea having a switchabl spare.
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