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Old 09-11-2021, 02:40 PM   #21
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Originally Posted by RT-NY View Post
...............So, would connecting the three main wires on the isolator to its center post work OK? If I am not mistaken, this would connect the alternator directory to the car battery and the house battery and bypass the isolator entirely,.................
Yes, that would effectively bypass the isolator.

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..............Would this effect the car wiring or charging system at all?
If it's a 3 post & 3 wire isolator then I can't think of any negative effects on the charging system. One benefit is that the chassis battery should now see higher charging voltage with because of no voltage drop through the isolator.

If there's more than 3 wires then report back & someone here should know what they're for.
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Old 09-12-2021, 06:29 PM   #22
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Default Dc to Dc Charger

It would be nice to see a step by step installation of the Renogy unit in a Older Roadtrek with the 3 post season isolator. Does anyone know if a video exists? Real words printed instructions?
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Old 09-12-2021, 10:18 PM   #23
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Default My D is connected directly to the battery. Always ON.

I have the 50amp renogy. It is always ON.

It wont charge if input voltage is less than 13v or so, so it automatically stops.

When the engine is ON, the voltage jumps to 14v, so it starts to charge.

I have a sprinter van.
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Old 09-12-2021, 10:42 PM   #24
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I have the 50amp renogy. It is always ON.

It wont charge if input voltage is less than 13v or so, so it automatically stops.

When the engine is ON, the voltage jumps to 14v, so it starts to charge.

I have a sprinter van.
Do you know whether it has any significant parasitic load when off?
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Old 09-12-2021, 11:52 PM   #25
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Do you know whether it has any significant parasitic load when off?

That is a good question, especially since it would likely be running off the quite small starting battery.


The other issue to check out with all chargers is how they initiate charge cycles. Engines can get started quite a few times during the day, so if for instance it ran a full charge timed cycle every time you started the engine it would not be very good for the coach batteries.


IMO, the best setup that is also pretty easy, would be a remote manual disconnect to the coach B to B charger with that disconnect connected directly to the alternator and starting battery. Alternator would then be referencing the starting battery like it did stock and you can shut off the entire power to the rear easily so no parasitic or charging unless you want it.
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Old 09-13-2021, 12:23 AM   #26
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The other issue to check out with all chargers is how they initiate charge cycles. Engines can get started quite a few times during the day, so if for instance it ran a full charge timed cycle every time you started the engine it would not be very good for the coach batteries.
Modern Transits have a very elaborate power management system. It can be run in various modes, but the best one (I think) involves a "load shed" signal that is supposed to be honored by the takeoff when the chassis decides that the alternator is heading toward being overloaded. The above scenario will need to be avoided in that case, as well. I THINK some of the better B2B systems have an input for this purpose, but I haven't gotten that far into things yet.
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Old 09-13-2021, 01:08 AM   #27
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Modern Transits have a very elaborate power management system. It can be run in various modes, but the best one (I think) involves a "load shed" signal that is supposed to be honored by the takeoff when the chassis decides that the alternator is heading toward being overloaded. The above scenario will need to be avoided in that case, as well. I THINK some of the better B2B systems have an input for this purpose, but I haven't gotten that far into things yet.

Without seeing the system on the Transit it is hard to know how they load shed, but without multiple alternators or singles with multiple fields and outputs I don't see how they could easily shed power to one area and not another. They could certainly have a way though. All the output reduction stuff I have seen reduced field current to reduce output and keep output in to keep temps in check or to improve mileage, so the Transit probably does similar so all feeds would go down together unless they shut them down completely to drop load.
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Old 09-13-2021, 01:42 AM   #28
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Default My D is connected directly to the battery. Always ON.

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Do you know whether it has any significant parasitic load when off?
I dont know exactly, but it is not much.

You can add a voltage sensor with a relay to turn the charger on if you want to.

I actually have a relay to switch between 2 dc-dc chargers I have. You can read my full config on this other post:

https://www.classbforum.com/forums/f...tml#post131422

Attached image is my full setup.
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File Type: png RV.Electric.Battery.png (263.9 KB, 9 views)
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Old 09-13-2021, 02:24 AM   #29
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Without seeing the system on the Transit it is hard to know how they load shed, but without multiple alternators or singles with multiple fields and outputs I don't see how they could easily shed power to one area and not another. They could certainly have a way though. All the output reduction stuff I have seen reduced field current to reduce output and keep output in to keep temps in check or to improve mileage, so the Transit probably does similar so all feeds would go down together unless they shut them down completely to drop load.
What I was describing was an output signal from the power management system to an external consumer such as the B2B. When the signal is asserted, the consumer is supposed to shut itself down until the signal is de-asserted. So, for instance, the B2B should stop charging the house battery for the duration. My point was that it would be bad if such an event restarted the charge cycle.
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Old 09-13-2021, 11:14 AM   #30
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What I was describing was an output signal from the power management system to an external consumer such as the B2B. When the signal is asserted, the consumer is supposed to shut itself down until the signal is de-asserted. So, for instance, the B2B should stop charging the house battery for the duration. My point was that it would be bad if such an event restarted the charge cycle.

Got it. I had the impression they were directly shedding the current to each area and that would be much harder to do. I wonder what the system does if you ignore the shut off signal?
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Old Today, 12:21 AM   #31
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I'd consider eliminating the isolator. Who needs an item in the system of no use, that can fail. Usually there is enough cable under the hood to "jump" the isolator (assuming it's near the battery).
I replaced the isolator with a manual switch and just used the cable that originally went from the isolator to the coach batteries as input for the Renogy 60 Amp charger. Works very well and has taken a load off my alternator. I also employed voltage sensitive switches to incorporate a delay to allow the alternator to warm up before charging starts and to lower the output when the coach battery voltage drops. This is described in an older thread.
Attached Images
File Type: jpg manual switch.jpg (143.3 KB, 1 views)
File Type: jpg DC-DC with controllers.jpg (291.4 KB, 0 views)
File Type: jpg DC-DC charging schematic.jpg (169.6 KB, 0 views)
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