DC-to-DC + Isolator

[markopolo]

Originally Posted by RT-NY

...............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.

Originally Posted by RT-NY

..............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.

[honeyboy]

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?

[ctarmor]

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.

[avanti]

Originally Posted by ctarmor

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?

[booster]

Originally Posted by avanti

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.

[avanti]

Originally Posted by booster

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.

[booster]

Originally Posted by avanti

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.

[ctarmor]

Originally Posted by avanti

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.

[avanti]

Originally Posted by booster

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.

[booster]

Originally Posted by avanti

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?

[reilym]

Originally Posted by rogerstg

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.

[Rlum]

Originally Posted by reilym

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.

Why did you install dc/dc charger? Were you having problems with your alternator. As you know, just installed the 2800i inverter generator. I am planning on running the generator when driving to charge up house lithiums with inverter/charger.

Don't drive long distances. I have a switch to turn off/on isolator. Currently when driving to keep refrigerator cold. I use the inverter to run it on 120volt. Next project will be to convert Dometic 3way to dc compressor fridge.

[reilym]

Originally Posted by Rlum

Why did you install dc/dc charger? Were you having problems with your alternator. As you know, just installed the 2800i inverter generator. I am planning on running the generator when driving to charge up house lithiums with inverter/charger.

Don't drive long distances. I have a switch to turn off/on isolator. Currently when driving to keep refrigerator cold. I use the inverter to run it on 120volt. Next project will be to convert Dometic 3way to dc compressor fridge.

I was unaware of the quiet Onan when I did this modification, but running the generator while driving never occurred to me.
When we bought the RV (used), the coach batteries were not charging from the alternator and I found that the 150 amp fuses in both cables (under the hood) had blown. I still don't know why and the previous owner was clueless. After replacing them, I found that the separator was also not functioning. After I had the system working, I frequently saw 150 amps going back to the batteries which is 70% of the alternator output. I was worried about this being too hard on the alternator if not the batteries. The DC-DC limits the alternator draw to 75 or so amps and I can remotely activate the LC to drop that further. I recently installed a temperature sensor on the alternator, but have not done any long road trips since installing it. I can disable or limit the current from DC-DC from the cab if the temps get too high.

On a related note, I was curious about the 2 fat cables that PW used going from the isolator back to the house batteries fused at 150 amps each. I speculate that since 2016 a transition year from AGM to lithium batteries in our model, they solved the problem of the lithiums taking as much current as you can throw at them by doubling up on the cabling. Photos of pre 2016 engine bays show only a single cable. In subsequent years, they moved the batteries into the coach (to avoid the low temperature charging limitations). I heard that PW now uses a DC-DC charger between the alternator and the coach batteries.

So far, we've had no problems with the Dometic 3 way fridge, but it does suck up the juice. If I am stopping for any length of time, I always run it off LP. However, I am interested in how the compressor fridge installation goes and your experience with it.

[Rlum]

Originally Posted by reilym

I was unaware of the quiet Onan when I did this modification, but running the generator while driving never occurred to me.
When we bought the RV (used), the coach batteries were not charging from the alternator and I found that the 150 amp fuses in both cables (under the hood) had blown. I still don't know why and the previous owner was clueless. After replacing them, I found that the separator was also not functioning. After I had the system working, I frequently saw 150 amps going back to the batteries which is 70% of the alternator output. I was worried about this being too hard on the alternator if not the batteries. The DC-DC limits the alternator draw to 75 or so amps and I can remotely activate the LC to drop that further. I recently installed a temperature sensor on the alternator, but have not done any long road trips since installing it. I can disable or limit the current from DC-DC from the cab if the temps get too high.

On a related note, I was curious about the 2 fat cables that PW used going from the isolator back to the house batteries fused at 150 amps each. I speculate that since 2016 a transition year from AGM to lithium batteries in our model, they solved the problem of the lithiums taking as much current as you can throw at them by doubling up on the cabling. Photos of pre 2016 engine bays show only a single cable. In subsequent years, they moved the batteries into the coach (to avoid the low temperature charging limitations). I heard that PW now uses a DC-DC charger between the alternator and the coach batteries.

So far, we've had no problems with the Dometic 3 way fridge, but it does suck up the juice. If I am stopping for any length of time, I always run it off LP. However, I am interested in how the compressor fridge installation goes and your experience with it.

My Victron shows 100 amp charging when using the alternator. Incidentally, fellow Facebook PW member has a 600ah lithium bank. He says he only charges from chassis alternator without any problems. Same year as ours. Also, I purchased my PW preowned from retired law enforcement officer. I use generator in addition to alternator to charge bank. I have Victron 3000/12 inverter charger combo. It puts out 80 amps on charging and is configured for lithium. Often will use the old Onan(not inverter) to charge and turn off alternator. I would do this so I could exercise the genny for a couple of hours. Good way to exercise if it has been a 4-6 weeks.

Dometic fridge is OK on propane when temps are below 90. I worry when we go camping and temps rise above 90. We live in SW part of USA so temps in summer time can easily rise above 100.

[booster]

I don't understand how a 600ah lithium bank can be charged with a chassis alternator that is also running the van without overheating it, unless there is some sort of current limiting. Many here would really like to know how that was done, I think.



Our 440ah AGM bank will overheat a 280 amp Nations alternator by pulling over 200 amps for long periods of time and lithium should take even more current.



Perhaps that person has a remote regulator that is set to limit field current. A Balmar can be made to reduce by 50% the output this way, saving the alternator.

[Rlum]

Originally Posted by booster

I don't understand how a 600ah lithium bank can be charged with a chassis alternator that is also running the van without overheating it, unless there is some sort of current limiting. Many here would really like to know how that was done, I think.



Our 440ah AGM bank will overheat a 280 amp Nations alternator by pulling over 200 amps for long periods of time and lithium should take even more current.



Perhaps that person has a remote regulator that is set to limit field current. A Balmar can be made to reduce by 50% the output this way, saving the alternator.

I do not know either. The person is a FB PW forum friend. He has the same yr (2016) Lexor TS as me. I do not camp/break camp every 48 hrs. Not really a traveler. Maybe he is not running his bank down entirely. 600ah lithium is difficult to use unless one is running air conditioning. Maybe when he is using ac, he is also recharging on site with generator?

He has made lots of upgrades to his van. I specifically asked him about the alternator. He said after 44K miles no issues with his alternator. At one time, he considered upgrading to heavier duty alternator but decided against it because he felt it was non issue?

How long does your Nations alternator take to overheat when putting out 200amps? Personally, my puts out about 100amps for about 1-2 hrs without issues? Now, I do not run my bank down too far. I have a large bank too. If I were concerned about the alternator. I would run my generator and converter. It puts out about 80 amps/hr.

Interesting perspective since I do not know if DC to DC charger is a requirement for me?

Thanks for your perspective!

[avanti]

I don't mean to criticize anyone in particular, but I am underwhelmed by these finger-in-the-wind approaches to building these large, energetic, expensive systems. Without either a Balmar-like-device that modulates alternator output or else a B2B that limits current draw, such systems appear to be relying on the ampacity of the feed wires as the primary current-limiting technique. This does not sound like a good idea to me.

I am also not fond of systems that depend on manual monitoring and configuration by a human in order to stay safe.

Again, no offense to anyone, but IMO, systems working at these power levels need to be actually engineered. I.e., the maximum currents need to be guaranteed, and all components need to be sized and fused accordingly. These things aren't really matters of opinion.

I am trying hard not to be snarky -- I enjoy messing around as much as anyone, and more than most. This just doesn't seem to be the right place to do so.

[booster]

Originally Posted by Rlum

I do not know either. The person is a FB PW forum friend. He has the same yr (2016) Lexor TS as me. I do not camp/break camp every 48 hrs. Not really a traveler. Maybe he is not running his bank down entirely. 600ah lithium is difficult to use unless one is running air conditioning. Maybe when he is using ac, he is also recharging on site with generator?

He has made lots of upgrades to his van. I specifically asked him about the alternator. He said after 44K miles no issues with his alternator. At one time, he considered upgrading to heavier duty alternator but decided against it because he felt it was non issue?

How long does your Nations alternator take to overheat when putting out 200amps? Personally, my puts out about 100amps for about 1-2 hrs without issues? Now, I do not run my bank down too far. I have a large bank too. If I were concerned about the alternator. I would run my generator and converter. It puts out about 80 amps/hr.

Interesting perspective since I do not know if DC to DC charger is a requirement for me?

Thanks for your perspective!

I have our setup to run parallel with two alternators a 250 amp and a 280 amp, both controlled off a single remote regulator, but when it was a single with the 250amp as the only one, it would get hot in about 20 minutes, but it all depends on what you consider hot. I don't like to go over 225*F or so, which is similar to what Balmar does on their remote regulator temp sensor turn down (we don't have a Balmar). Some people are OK with 245* and higher, but most manufacturers don't like that.



The Chevy that we have doesn't get great air to the alternators so they run hotter than most, I think. We will get both to 225* in about 20 minutes at 280 amps and depending on if it is very hot out it can get that hot at lower outputs as low as 200 amps. There is also about 20 amps going the run the van also.


Avanti posted a current log trace from his 280 amp alternator to his 440ah AGMs so he can probably know how long it took to get to the first cool down current reduction and what amps it was running at the time. I would guess most systems would get to 225* in less than 30 minutes though at 200 amps from a 280amp alternator with no van load.

[avanti]

Originally Posted by booster

\Avanti posted a current log trace from his 280 amp alternator to his 440ah AGMs so he can probably know how long it took to get to the first cool down current reduction and what amps it was running at the time. I would guess most systems would get to 225* in less than 30 minutes though at 200 amps from a 280amp alternator with no van load.

That test was done on a very hot day, and the battery was initially drawing 215 amps. Under those conditions, the Balmar started to cycle down the current (to 140 amps) within 5 minutes, and continued to cycle up and down every 5-10 minutes for almost an hour, until the demand tapered to around 150 amps, at which point I started seeing a near-perfect exponential decline, asymptoting toward zero, showing 7 amps after 200 minutes.

[Rlum]

Originally Posted by reilym

I was unaware of the quiet Onan when I did this modification, but running the generator while driving never occurred to me.
When we bought the RV (used), the coach batteries were not charging from the alternator and I found that the 150 amp fuses in both cables (under the hood) had blown. I still don't know why and the previous owner was clueless. After replacing them, I found that the separator was also not functioning. After I had the system working, I frequently saw 150 amps going back to the batteries which is 70% of the alternator output. I was worried about this being too hard on the alternator if not the batteries. The DC-DC limits the alternator draw to 75 or so amps and I can remotely activate the LC to drop that further. I recently installed a temperature sensor on the alternator, but have not done any long road trips since installing it. I can disable or limit the current from DC-DC from the cab if the temps get too high.

On a related note, I was curious about the 2 fat cables that PW used going from the isolator back to the house batteries fused at 150 amps each. I speculate that since 2016 a transition year from AGM to lithium batteries in our model, they solved the problem of the lithiums taking as much current as you can throw at them by doubling up on the cabling. Photos of pre 2016 engine bays show only a single cable. In subsequent years, they moved the batteries into the coach (to avoid the low temperature charging limitations). I heard that PW now uses a DC-DC charger between the alternator and the coach batteries.

So far, we've had no problems with the Dometic 3 way fridge, but it does suck up the juice. If I am stopping for any length of time, I always run it off LP. However, I am interested in how the compressor fridge installation goes and your experience with it.

I know lots of folks have DC to DC chargers installed to preserve and increase life of alternators. How about an easier/simpler solution. Use an XP270 or XP370 alternator? Aside from the cost compared to the DC to DC chargers, what other issues do you see installing a different alternator?