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07-27-2023, 11:17 AM
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#1
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2 Rivet Member
2020 16' Basecamp
Gallatin
, Tennessee
Join Date: Jul 2023
Posts: 54
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Help me Understand DC to DC charging
I am new to all of this and I have some questions that I am not wrapping my head around.
I have a 2020 Basecamp 16X. When I connect my Tow Vehicle with the 7 pin connector, does the Vehicle charge the battery?
If so what is the need for the DC to DC charger?
I am sorry for possibly the most simple question, but I am new and trying to understand.
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07-27-2023, 12:29 PM
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#2
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Rivet Master
1988 25' Excella
1987 32' Excella
Knoxville
, Tennessee
Join Date: Oct 2010
Posts: 5,210
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When you connect the 7 pin the TV may or may not charge the battery in the trailer. There is a long wire span to the trailer battery and the voltage drops in that run so that charging is either slow or not at all. The TV voltage regulator sees the TV battery and lowers the charge voltage with it is charged. A DC to DC charger mounted on the trailer takes in the the low voltage coming to it from the car alternator and reproduces a correct voltage for charging. I think of it as a battery charger operated by the TV. You can get a DC to DC charger in a wide range of charging capacities. If you get one over 12 or so amps you will probably need a seperate, dedicated charge line to it from the TV battery with a fuse and its own connector.
If your trailer has an 12 volt electric fridge rather than a propane fridge and/or lithium batteries you are almost sure to want/need a DC to DC converter.
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07-27-2023, 01:29 PM
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#3
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Rivet Master
2019 27' Globetrotter
McHenry
, Illinois
Join Date: Apr 2018
Posts: 2,462
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Great question to a confusing subject
thedantons, you’re in the right place! We all come here to learn from each other. Bill M gave a good explanation. A DC-DC charger will provide more current to your trailer’s battery than the 7-Pin cable can provide.
They’re available in different sizes of output; choose the one that matches your needs. I recently replaced our two AGM batteries with a Battle Born GC3 270Ah battery and installed a Renogy 40A DC-DC charger. This allows us to run our 3-way fridge on 12V while underway vs. risking propane.
A DC-DC charger does required larger cables run from the two vehicle’s battery to the bumper with an Anderson connector to the trailer’s section. I used 4 AWG welding cable (more flexible) and a 60A fuse at the battery.
I took a screen shot of my Victron BVM-712 battery monitor showing 28A going to the trailer’s battery while on the road. The other benefit is this works all the time unlike solar on a rainy day or after dark.
Hope that helps!
__________________
2019 27’ Globetrotter FBT Walnut/Dublin Slate
2018 FC23FB
2019 Ram 2500 6.4 Hemi Laramie Blue Ox 1000#
WBCCI# 10258
RETIRED!
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07-27-2023, 01:35 PM
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#4
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Site Team
1994 25' Excella
Waukesha
, Wisconsin
Join Date: Sep 2020
Posts: 6,196
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The short answer is that yes, your trailer batteries will get a charge from the 7-wire harness connection while your tow vehicle is running. How much of a charge requires a longer answer.
If you're running with a propane/electric fridge you should be fine with the regular setup as long as you have shore power or a generator often enough to get the batteries fully charged once in a while. If you have a 12v fridge or other high-draw 12v devices, then you might want to consider solar charging or a DC-to-DC charger.
The big advantage to the DC-to-DC charger is that it will ensure you have the optimum voltage for your trailer batteries sent through for charging, not just whatever happens to be the voltage level of the tow vehicle's system. For lithium batteries this is even more important.
__________________
Richard
11018
1994 Excella 25 'Gertie' Follow the build on Gertie!
1999 Suburban LS 2500 w/7.4L V8 'Bert'
1974 GMC 4108a - Custom Coach Land Cruiser 'The Bus' (Sold)
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07-27-2023, 02:36 PM
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#5
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2 Rivet Member
2020 16' Basecamp
Gallatin
, Tennessee
Join Date: Jul 2023
Posts: 54
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Than you all for this information. I guess more information would be needed. When I purchased the camper they had just installed two new Dakota Lithium batteries. It does have solar and I am running a 12v fridge.
The batteries are not charging to 100% on shore power. ( I have identified I need to upgrade my converter to WF-8955-AD-MBA or something similar.)
the other question was the DC to Dc charging. Since all this electrical stuff is new to me, I am not sure what I even need to look at. I have a Victron MPPT 75/15 and a 712 BMV. So, I was looking at the Victron Orion, but not sure which one I would need.
I also did not know if I needed to run a new wire to the battery or if I wired off of the 7 pin inside the camper.
I hope my rambling is not too bad. Thanks again
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07-27-2023, 02:43 PM
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#6
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Site Team
1994 25' Excella
Waukesha
, Wisconsin
Join Date: Sep 2020
Posts: 6,196
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Quote:
Originally Posted by thedantons
Than you all for this information. I guess more information would be needed. When I purchased the camper they had just installed two new Dakota Lithium batteries. It does have solar and I am running a 12v fridge.
The batteries are not charging to 100% on shore power. ( I have identified I need to upgrade my converter to WF-8955-AD-MBA or something similar.)
the other question was the DC to Dc charging. Since all this electrical stuff is new to me, I am not sure what I even need to look at. I have a Victron MPPT 75/15 and a 712 BMV. So, I was looking at the Victron Orion, but not sure which one I would need.
I also did not know if I needed to run a new wire to the battery or if I wired off of the 7 pin inside the camper.
I hope my rambling is not too bad. Thanks again
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With this additional information, you may or may not need the DC-to-DC charger. If you do all your traveling during daylight hours, then you'll be able to get a pretty decent charge on the road, up to 15 amps. May not fully charge the batts, but it will go a long way. However, on short travel days or during night time travel or bad weather you will get little to no charging from the solar.
You can install an Orion 12/12-18 using the stock wiring in your 7-wire connection the truck and get up to 18 amps of charging. If that's enough to augment what you already have from the solar, then it's the easiest way to go. If you need a larger (higher output) DC-to-DC charger, you'd be best to install a dedicated pair of wires from the truck's battery to the rear bumper where you can directly connect the DC-to-DC charger in the trailer. This will allow higher current charging.
__________________
Richard
11018
1994 Excella 25 'Gertie' Follow the build on Gertie!
1999 Suburban LS 2500 w/7.4L V8 'Bert'
1974 GMC 4108a - Custom Coach Land Cruiser 'The Bus' (Sold)
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07-27-2023, 06:23 PM
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#7
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2 Rivet Member
2020 16' Basecamp
Gallatin
, Tennessee
Join Date: Jul 2023
Posts: 54
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Quote:
Originally Posted by richard5933
With this additional information, you may or may not need the DC-to-DC charger. If you do all your traveling during daylight hours, then you'll be able to get a pretty decent charge on the road, up to 15 amps. May not fully charge the batts, but it will go a long way. However, on short travel days or during night time travel or bad weather you will get little to no charging from the solar.
You can install an Orion 12/12-18 using the stock wiring in your 7-wire connection the truck and get up to 18 amps of charging. If that's enough to augment what you already have from the solar, then it's the easiest way to go. If you need a larger (higher output) DC-to-DC charger, you'd be best to install a dedicated pair of wires from the truck's battery to the rear bumper where you can directly connect the DC-to-DC charger in the trailer. This will allow higher current charging.
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Thank you again. What is the best way to identify the proper cables coming from the 7 pin connector in the camper? should it be going to the bus bar? I think this may be the direction that I try to go. Is there a calculation that tells me how much the 18 amps will charge a battery? I know it will be in conjunction with the solar, but trying to figure out if I should give this a try or buy a bigger using and just be done with it. I think there is a Victron dealer not too far from my house that I may call and talk it through with them to see what they say also, but I know they ultimately want to sell me something.
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07-27-2023, 07:27 PM
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#8
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Rivet Master
2012 25' FB Eddie Bauer
Vintage Kin Owner
Virginia Beach
, Virginia
Join Date: Sep 2004
Posts: 7,801
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Go to an Airstream or Airforums rally or camp at an Airstream dominant campground and look pathetic. Join WBCCI / The Airstream Club.
Look ignorant and eager... in six months you'll be ready to do it with your blue beret on, and you'll become a grizzled veteran I your second year.
Paula the fossil Ford
__________________
Today is a gift, that's why they call it the present.
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07-27-2023, 10:28 PM
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#9
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Site Team
1994 25' Excella
Waukesha
, Wisconsin
Join Date: Sep 2020
Posts: 6,196
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Quote:
Originally Posted by thedantons
Thank you again. What is the best way to identify the proper cables coming from the 7 pin connector in the camper? should it be going to the bus bar? I think this may be the direction that I try to go. Is there a calculation that tells me how much the 18 amps will charge a battery? I know it will be in conjunction with the solar, but trying to figure out if I should give this a try or buy a bigger using and just be done with it. I think there is a Victron dealer not too far from my house that I may call and talk it through with them to see what they say also, but I know they ultimately want to sell me something.
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Assuming that this is a 2020 Basecamp, the manual shows a black 10 ga wire coming from the 7-wire harness to the positive bus bar which is bringing the 12v charge in from the tow vehicle. This wire would be pulled from the bus bar and connected to the positive input side of the DC-to-DC charger, and then the positive output from the DC-to-DC charger would be connected to the bus bar in the place you took this wire from. There are more connections to be made, so don't take this as the whole process, and you need to confirm with a volt meter to make sure that the correct wire is identified. The manual for the DC-to-DC charger AND the manual for your trailer (wiring diagram) should be used here.
Calculation for charging? It's just counting beans. If you have, let's say, two 100-amp hour (Ah) capacity batteries that gives you a total capacity of 200 Ah. When you wake up in the morning your battery monitor shows that you've used up 90 Ah running a few devices overnight. If you are going to recharge them using just the DC-to-DC charger with a max of 18 amps output, that means that you can replenish at a rate of 18 amps of capacity per hour. The calculation of 90/18=5 shows that it would take 5 hours to replenish the 90 Ah you used overnight.
Then you'll add on top of this the potential charging ability of the solar panels.
Whether the 12/12-18 Orion is enough for your needs is impossible for anyone but you to determine. Do the math and see. You need to take into account your battery bank capacity, the amount of power you'll consume overnight, etc. Also in the calculation would be how much capacity your tow vehicle's wiring can send to the 7-wire connection. A starting point for this would be to see what fuse controls the charge circuit going to the 7-wire harness along with the size of the wire being used.
__________________
Richard
11018
1994 Excella 25 'Gertie' Follow the build on Gertie!
1999 Suburban LS 2500 w/7.4L V8 'Bert'
1974 GMC 4108a - Custom Coach Land Cruiser 'The Bus' (Sold)
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07-28-2023, 10:09 AM
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#10
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2 Rivet Member
Wayne
, New Jersey
Join Date: Mar 2022
Posts: 22
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Great question and responses
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07-28-2023, 10:18 AM
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#11
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Rivet Master
2017 23' Flying Cloud
Parker
, Colorado
Join Date: Oct 2016
Posts: 1,772
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Great info and advice as always.
Since you do have lithium batteries it is also a good idea to have the dc to dc charger to isolate the trailer battery from the car battery. This is often overlooked. The lithium battery has a higher charge state so if you connect to the the tow vehicle then you can actually drain the lithium as it will try and “charge” the tow vehicle battery with lower voltage.
This happened to a pal of mine. He didn’t want to install the dc to dc charger, so we simply removed the fuse for the trailer plug from the tow vehicle to isolate the two. You don’t want the lithium discharging to the TV.
Also. You don’t have to run a new line from the battery if you are okay with a very low amp. If you want more amps (like 28 above) then you will have to run a new line. The small gage wire on the existing trailer plug limits how much you can get.
__________________
Thanks,
Troutboy
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07-28-2023, 10:23 AM
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#12
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New Member
1983 34' Excella
Bellingham
, Washington
Join Date: Nov 2016
Posts: 1
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Lithium batteries require a higher charging voltage than your vehicle's alternator will put out. the DC to DC charger will convert the alternator voltage to what's required. Your shore power converter may not be rated for Lithium batteries. As an option to a new converter, I installed a 120V lithium battery charger.
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07-28-2023, 10:55 AM
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#13
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Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle
, Pennsylvania
Join Date: May 2017
Posts: 16,544
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Hi
Just what you do is very much up to you. I would suggest that to get any real charging from your TV, you need a DC/DC. Will solar "keep up"? It might on a good day. On a bad day ... not so much. How lucky do you feel?
These days, the normal Victron choice for a DC/DC is:
https://shop.pkys.com/Victron-Energy...er_p_8042.html
There are other very similar 18A Orion versions. The "Smart" version with Bluetooth along with a few control features make this one what most folks go with today.
Hookup wise, 12V wire from the 7 pin comes off the DC bus bar. That wire goes to the input on the Orion. Wire from the output of the Orion goes to the bus bar. Negatives both go to the ground bus bar.
Once it's in, you play with settings. There are various threads about all that. The key points are changing things to match lithium and setting the input cutout voltage to 9 or 10V.
Not a really crazy project.
Bob
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07-28-2023, 11:26 AM
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#14
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2 Rivet Member
2020 16' Basecamp
Gallatin
, Tennessee
Join Date: Jul 2023
Posts: 54
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Quote:
Originally Posted by richard5933
Assuming that this is a 2020 Basecamp, the manual shows a black 10 ga wire coming from the 7-wire harness to the positive bus bar which is bringing the 12v charge in from the tow vehicle. This wire would be pulled from the bus bar and connected to the positive input side of the DC-to-DC charger, and then the positive output from the DC-to-DC charger would be connected to the bus bar in the place you took this wire from. There are more connections to be made, so don't take this as the whole process, and you need to confirm with a volt meter to make sure that the correct wire is identified. The manual for the DC-to-DC charger AND the manual for your trailer (wiring diagram) should be used here.
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This is a 2020 Basecamp. I have looked at the electrical diagram that is in the user manual. I will look at it with more detail. I did notice one bus bar with all red wires and one back. I will look in better detail, but that must be the wire coming from the TV 7 pin connector.
Thank you everyone for the kind advice and worm welcomes. I am learning more and more everyday.
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07-29-2023, 12:14 AM
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#15
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Rivet Master
2017 23' Flying Cloud
Parker
, Colorado
Join Date: Oct 2016
Posts: 1,772
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FYI. We went out today for a 3 day trip. In the driveway with truck running I was getting 6-8 amps of charging power to my lithium’s. This is using trailer plug wiring and the Orion.
Thanks
__________________
Thanks,
Troutboy
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07-29-2023, 12:43 AM
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#16
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4 Rivet Member
2004 22' International CCD
Beaumont
, California
Join Date: Jan 2021
Posts: 488
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Vehicles’ voltage regulators do not lower the voltage output based on battery state-of-charge. Voltage applied to the vehicle’s battery is a constant 13.8-14.8, depending on ambient temperature: the warmer outside air is, the lower the voltage. The cooler the outside air temp, the higher the voltage. This variable is designed to overcome higher battery resistance in winter and to reduce electrolyte evaporation in summer. What DOES reduce as battery charge approaches full, is current flow.
The voltage applied (received) to a trailer battery is not reduced by the TV system: it is reduced by a basic property described by Ohm’s Law, in this case, higher current flow causes voltage drop at the end of the circuit (battery). The more charged a common lead-acid battery is, the less current it needs to complete the charge. As current draw goes down, applied voltage increases as voltage drop decreases. I.e., if you have a battery at 50% charge, it could draw 15 amps from the TV alternator, which, when running, would be producing approximately 14.5 volts with an ambient temp of 30 degrees F. But due to voltage drop caused by wire resistance and connections resistances, an applied trailer battery voltage of just 12.3 volts could be the condition. However, as the battery approaches a full charge, current flow reduces, which reduces voltage drop, and so applied voltage increases.
Eventually, when the trailer battery is at, say, 98% charged, the current flow would be so low that the applied voltage would be nearly the 14.5 volts.
The numbers I’ve used are for example; exact voltages will vary by battery charge state (both TV and trailer), TV actual voltage output (which varies somewhat by make), battery type, battery age, and circuit resistances.
So, if you have a long, old trailer being pulled by an old TV with lots of charging circuit resistance, you will have different charging characteristics compared to a 2023 TV pulling and charging a 2023 little trailer.
The DC -DC charger is a great solution for this; more importantly, it addresses the difference in charging characteristics between lead-acid and lithium batteries.
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07-29-2023, 07:05 AM
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#17
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Rivet Master
2007 30' Classic
Oswego
, Illinois
Join Date: Jul 2010
Posts: 13,711
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"Vehicles’ voltage regulators do not lower the voltage output based on battery state-of-charge. Voltage applied to the vehicle’s battery is a constant 13.8-14.8,"
While this was true with "dumb" alternators, it is not true anymore.
Sent from my SM-S901U using Airstream Forums mobile app
__________________
-Rich-
"If the women don't find you handsome, they should at least find you handy." - Red Green
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07-29-2023, 05:59 PM
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#18
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3 Rivet Member
2021 16' Caravel
Fullerton
, California
Join Date: Dec 2020
Posts: 126
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thedantons,
On a trip back in February, we had rain/cloud cover and trees at campsites. Solar was not producing enough to keep our two 100amp BB lithiums charged, and the trickle from the 7 way wasn't helping. We resorted to our generator which I hate doing. So, upon returning home, I decided it was time to install a DC-DC charger.
I chose the Victron Orion-Tr Smart 12|12-18amp ($169) because 18 amps is enough for our 4-6 hour driving days. I also didn't want to add additional connectors and wires to my TV. As usual, I turned to amsolar.com for info and proper wiring, and found the attached VERY clean diagram. With that in hand, wiring was straight forward.
https://a.co/d/gAGq61F
I hope this helps.
Bob
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07-30-2023, 07:40 AM
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#19
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Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle
, Pennsylvania
Join Date: May 2017
Posts: 16,544
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Hi
Regardless of what the voltage regulator may or may not do, the alternator is spinning at a speed related to engine RPM's. Your gas engine might idle at some crazy 500 rpm and spins up to an equally crazy 6,000 rpm. That's a lot of range for the alternator to function over.
The faster the alternator spins, the more current it *can* put out. It only will put out as much current is needed. The point is only that it can do (much) better at higher RPM's.
On vehicle with a conventional ( = old) control system, as you sit there in traffic, the idle drops back to a low number. The alternator struggles with the load, the voltage drops. Fancier setups might rev the engine and play with the transmission to help this out.
When you look at the bold print rating on your alternator, it is talking about the "6,000 RPM" number. (The alternator is on its own pulley so the actual alternator RPM's are not engine RPM's, still there is a direct relation). When the alternator is spinning at (maybe) 1/10th those RPM's, it can't put much out. The voltage to your trailer likely suffers as a result.
Bob
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08-02-2023, 10:33 AM
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#20
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Rivet Master
2021 30' Flying Cloud
Airstream - Other
Airstream - Other
Lady Lake
, Florida
Join Date: Mar 2018
Posts: 1,284
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It works
Our Victron 30 amp Dc -DC installed by Ronnie Dennis works flawlessly. All you need to know. Install it professionally forget it it works.
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