Variable voltage alternator or not - 2017
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Cross-Country
Joined: Feb 2021
Posts: 57
Likes: 3
From: Perth, Australia
Variable voltage alternator or not - 2017
Hi all,
I have a 2017 F-250 Super Duty Lariat. I have a sparky about to wire it up to power the DC charger in the caravan. The common wiring is to place an isolator inline on the ute to stop the battery drain when the vehicle is off. The isolator allows current through from the vehicle to the caravan when the engine is running. When the ignition is switched to off the switch wire becomes dead and the isolator senses the voltage drop to about 12.7V, it cuts the circuit between the ute batteries and the caravan. I've been asked if the alternators in the 2017 are variable voltage. I have searched the forum and can't find any information other than the "charge system is variable ... as the state of the charge changes ... the alternator output changes".
Can anyone confirm that the 2017 models have variable voltage alternators or not?
Thanks in advance,
Trevor
I have a 2017 F-250 Super Duty Lariat. I have a sparky about to wire it up to power the DC charger in the caravan. The common wiring is to place an isolator inline on the ute to stop the battery drain when the vehicle is off. The isolator allows current through from the vehicle to the caravan when the engine is running. When the ignition is switched to off the switch wire becomes dead and the isolator senses the voltage drop to about 12.7V, it cuts the circuit between the ute batteries and the caravan. I've been asked if the alternators in the 2017 are variable voltage. I have searched the forum and can't find any information other than the "charge system is variable ... as the state of the charge changes ... the alternator output changes".
Can anyone confirm that the 2017 models have variable voltage alternators or not?
Thanks in advance,
Trevor
Fleet Mechanic
Joined: Feb 2021
Posts: 1,405
Likes: 1,171
From: East TN
All alternators are variable voltage. What you really need to know is how the voltage regulator functions. Why not just wire a 100+ amp contactor that is controlled by the "hot in run" circuit in your F-250? Engine on, charging is on. Engine off, charging off. Simple, cheap.
Hotshot
Joined: Jul 2013
Posts: 14,266
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your alternators are "SMART" computer controlled alternators. typically 14.5 volts upon crank up to recharge the batteries after startup and if there is a large load....but will meter down to 13.75 - 14,25 once batteries are fully charged and no significant load.
if you have dual alternators, they are not redundant....meaning if one fails the other takes over and the CPU does not switch between primary and secondary.......dual alternators work in the same manner as "SMART" alternators do with the exception that the secondary will kick in to provide current once the current rating of the primary is reached.
if you have dual alternators, they are not redundant....meaning if one fails the other takes over and the CPU does not switch between primary and secondary.......dual alternators work in the same manner as "SMART" alternators do with the exception that the secondary will kick in to provide current once the current rating of the primary is reached.
Thread Starter
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Cross-Country
Joined: Feb 2021
Posts: 57
Likes: 3
From: Perth, Australia
Hi,
Thanks for your comments.
Thinking about this overnighht I realize that the auto electrician has got this wrong. He's talking about the DC changer in the caravan. The charger will isolate vehicle when it senses voltage drop. This isn't going to be a problem as per below.
The intention is to do exactly what you've suggested B-Man FX4. I think we'll take an upfitter wire as a hot switch wire to the isolator. Is that where you'd get your 'hot in run' wire?
Thanks for your comments.
Thinking about this overnighht I realize that the auto electrician has got this wrong. He's talking about the DC changer in the caravan. The charger will isolate vehicle when it senses voltage drop. This isn't going to be a problem as per below.
The intention is to do exactly what you've suggested B-Man FX4. I think we'll take an upfitter wire as a hot switch wire to the isolator. Is that where you'd get your 'hot in run' wire?
Fleet Mechanic
Joined: Feb 2021
Posts: 1,405
Likes: 1,171
From: East TN
An upfitter switch would work but it isn't "automatic". As long as you remember to turn it on and off you are obviously fine.
On 2017 - 2021 trucks there is a "customer access" wire bundle in the footwell of the passenger side cab. In that bundle is a green / orange wire that is connected to Fuse 22 in the BCM. It is fused for 5 amps and is hot in Start or Run mode. As long as you select a contactor that draws less than 5 amps when energized you should be fine using this circuit to power it. You should select a contactor rated for 100% duty cycle, or 'continuous duty" as some label it. Here's one from a quick search but I'm sure you can find something comparable "down under".
12VDC 200 Amp Continuous Duty Contactor With 150ma Coil
On 2017 - 2021 trucks there is a "customer access" wire bundle in the footwell of the passenger side cab. In that bundle is a green / orange wire that is connected to Fuse 22 in the BCM. It is fused for 5 amps and is hot in Start or Run mode. As long as you select a contactor that draws less than 5 amps when energized you should be fine using this circuit to power it. You should select a contactor rated for 100% duty cycle, or 'continuous duty" as some label it. Here's one from a quick search but I'm sure you can find something comparable "down under".
12VDC 200 Amp Continuous Duty Contactor With 150ma Coil
Mountain Pass
Joined: Dec 2020
Posts: 227
Likes: 95
From: Southcentral Alaska
Your "sparky" is likely installing a DC-DC charger/controller - maybe a Renogy or Victron unit. If so, it may be a model with the Isolation feature built in: no juice from the alternator=engine off=open the circuit and protect the truck batteries from thirsty RV batteries. I recently installed a Victron 18 amp DC-DC isolating charger/controller for that reason, and because it "talks" bluetooth to an app that tells me exactly what it is doing. No upfitter required, no remembering to move the switch when distracted by other arrival or departure stuff, no need to unplug the 7-pin pigtail as some practice. I chose the 18 amp rather than the 30 amp model, due to the relatively small 10ga wire in the circuit - resistance limits the amount of juice that flows over such a small wire without getting warm.
First test showed the truck was sending 13 amps and 13.5 volts to the trailer LiFePo batteries at idle. Note that the drill included putting the truck in tow/haul and pushing on the brake before the charging started. Haven't done a highway test yet... may be a while as someone pulled in front of me a few weeks ago and probably won't see the truck again for a few months.
First test showed the truck was sending 13 amps and 13.5 volts to the trailer LiFePo batteries at idle. Note that the drill included putting the truck in tow/haul and pushing on the brake before the charging started. Haven't done a highway test yet... may be a while as someone pulled in front of me a few weeks ago and probably won't see the truck again for a few months.
Hotshot
Joined: Oct 2015
Posts: 19,698
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From: Wyoming
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