Minimum acceptable alternator voltage?

[Avery4]

The 1998 Nissan Frontier does have a relay for the "12V power outlet". It does not have a relay for the "cigarette lighter socket". Yes, it has two sockets. Yes, both are only live when the key is ON (or probably also accessory).

Interesting, I've never seen that before. I wonder why they did that. The only practical benefit I can think of to running a power outlet circuit through its own relay instead of just using the ignition switch is saving wear on the switch's contacts if someone is always turning it on and off with a heavy load on the circuit, but the majority of the time I bet that relay draws half as much current as the phone charger or whatever else someone has plugged into it and it will consume a small amount of power whenever the key is on whether the outlet is being used or not, which is obviously a slight downside.

 

[brianl703]

Interesting, I've never seen that before. I wonder why they did that.

I think they expected it, the Nissan Frontier being a utilitarian pickup truck, to have an inverter or high-wattage lighting or a ham radio or something else that uses a lot of power connected. It's very clearly marked as a 12V power outlet, so you know that's the one to use as opposed to the cigarette lighter socket.

And using a relay takes this potential load off of the ignition switch. Same reason why most car stereo head units pull the bulk of the power they use from the constant 12V wire instead of the switched wire.

 

[Dave9]

Interesting, I've never seen that before. I wonder why they did that. The only practical benefit I can think of to running a power outlet circuit through its own relay instead of just using the ignition switch is saving wear on the switch's contacts if someone is always turning it on and off with a heavy load on the circuit, but the majority of the time I bet that relay draws half as much current as the phone charger or whatever else someone has plugged into it and it will consume a small amount of power whenever the key is on whether the outlet is being used or not, which is obviously a slight downside.

Anything switched that has significant current might benefit from a relay, until you reach the practical limits of what a relay can handle, for example that's not going to happen for the starter motor windings feed. This (usually) saves on wire cost and bulk, and yes a switch doesn't have to be built nearly as robustly, and lasts longer, if it is only switching a logic level signal or at least as little current as possible, particularly when it is DC current. Relays are specifically designed to be optimal for this, or in more modern vehicles, transistor switching.

Relay current is typically negligible, maybe 150mA. If it allows more directly routing, shorter wires, then you trade off having less loss in the wire. Either way, it's a small drop in the bucket on a vehicle using tens of amps and with a power dense fuel source like gasoline.

Besides, there are many things that might turn on with the ignition, if that includes (n ) x 15A lighter/power outlets in addition to everything else, consider how large/low the wire gauge would have to be, running up through the steering column, and the extra space the physically larger (and more expensive) switch would have to take up. Plus, in the long term a relay is considered a wear item, is easier and less expensive to just unplug the old and plug in the new.

 

[Avery4]

Anything switched that has significant current might benefit from a relay, until you reach the practical limits of what a relay can handle, for example that's not going to happen for the starter motor windings feed. This (usually) saves on wire cost and bulk, and yes a switch doesn't have to be built nearly as robustly, and lasts longer, if it is only switching a logic level signal or at least as little current as possible, particularly when it is DC current. Relays are specifically designed to be optimal for this, or in more modern vehicles, transistor switching.

Relay current is typically negligible, maybe 150mA. If it allows more directly routing, shorter wires, then you trade off having less loss in the wire. Either way, it's a small drop in the bucket on a vehicle using tens of amps and with a power dense fuel source like gasoline.

Besides, there are many things that might turn on with the ignition, if that includes (n ) x 15A lighter/power outlets in addition to everything else, consider how large/low the wire gauge would have to be, running up through the steering column, and the extra space the physically larger (and more expensive) switch would have to take up. Plus, in the long term a relay is considered a wear item, is easier and less expensive to just unplug the old and plug in the new.

That's a good point, I'm just not sure how many people use the power outlet for a heavy enough load to benefit from a direct relay switched power feed. My car's outlet is wired with about 20 gauge wire and is only rated for 10 amps but the most I usually see those outlets used for is a phone charger, which normally draws well under 1 amp. I haven't seen those types of cigarette lighters used for years. But if I had a need to run something like a power inverter inside the car, I would definitely install a separate outlet with it's own fuse and a relay if I wanted it to be switched.

I have seen small relays draw around 0.2 amps and I have also seen larger relays for loads like blower motors, defrosters, etc draw as much as 0.5 amps. It certainly isn't a significant draw, but nonetheless it is still an extra load that is likely to use more power than the load it's supplying if it's supplying, which is often nothing. This won't matter much unless someone regularly leaves the key on without the engine running to charge their phone, listen to the radio, etc for long periods of time though and obviously wouldn't cause a problem under normal conditions unless the battery is very weak to begin with.

Overall I would agree that a relay switched outlet is a better design for the reasons you stated, I just don't see it benefiting the majority of drivers all that much.

 

[sky jumper]

Sure. Here's a diagram for my Honda Civic. I assume plenty of other cars have a similar setup since the lighter circuit is often only live with the key on and I have never seen a vehicle with a separate relay just for the lighter socket. And since the ignition switch is only fed with about a 12 gauge wire all the way from the underhood fusebox, it's easy to see how there could be a measurable voltage drop at the lighter outlet.

View attachment 90183

can you provide the link to this? or otherwise share the whole relevant document pages? I am quite certain the diagram you show is a simplified view that doesn't explicitly show the relay that is almost certainly part of the fuse/relay box. I refuse to believe honda would put 15A through the ignition switch. that would violate over 70 years of engineering best practice.

I have never seen, in any application including lawnmowers, an ignition switch powering anything more than a small light bulb or relay coil. and in many cases it powers a lower power relay that in turn powers the coil of a higher power relay. John Deere has a retrofit kit that does exactly that because the switch can't drive the starter relay coil.
https://www.greenpartstore.com/John-Deere-Starting-Improvement-Relay-Kit-AM107421.html

 

[Avery4]

can you provide the link to this? or otherwise share the whole relevant document pages? I am quite certain the diagram you show is a simplified view that doesn't explicitly show the relay that is almost certainly part of the fuse/relay box. I refuse to believe honda would put 15A through the ignition switch. that would violate over 70 years of engineering best practice.

I have never seen, in any application including lawnmowers, an ignition switch powering anything more than a small light bulb or relay coil. and in many cases it powers a lower power relay that in turn powers the coil of a higher power relay. John Deere has a retrofit kit that does exactly that because the switch can't drive the starter relay coil.
https://www.greenpartstore.com/John-Deere-Starting-Improvement-Relay-Kit-AM107421.html

Unfortunately I can not provide a link to those diagrams, I downloaded a bunch of diagrams from the BBB Industries website before they removed that feature. However, I currently own two of those cars and K24 swapped one of them, so I can confirm that this is in fact the case. As a test, I removed every single relay one at a time and the socket still had power with the key on. I think they are just counting on no one using the socket for anything substantial.

The starter solenoid is also directly energized by the ignition switch, there is no starter relay except to interrupt the circuit if the clutch isn't disengaged or the auto trans is in gear, but the relay can be jumpered and the starter will still work normally with the exception of always being available.

Even the fuel pump's power feed is run through the ignition switch. When I K24 swapped one of my Civics, I simply jumped the fuel pump relay as a temporary solution to get the fuel pump to run and it now just runs whenever the key is on.

I agree that these are somewhat odd design decisions, but it seems to work fine since 7th gen Civics aren't known for the ignition switches failing. My 04 has 115K miles and my 05 has 270K miles and both are on their original ignition switches with no trouble from either. It does look pretty heavy duty though, the terminals are thick and all the wires going to it are at least 12 gauge and possibly 10 gauge. There's no way Honda would have made the switch and its wiring so heavy duty if all it was doing was switching relays and other very light loads.

 

[sky jumper]

that is crazy. if you have an old spare you should dissect it and post pics i'd love to see the contacts. i've never owned a honda but my wife did years ago, a 99 accord. it had all kinds of electrical gremlins. I wonder if hers had such a switch. but that car was terrible. one day the harmonic balancer fell off while she was driving. we were still dating and she called me and told me what the shop said. I refused to believe it until I saw it with my own eyes. turns out the crank was bent and that probably caused the bolt to work loose. I've never seen anything like it. end of the crank was all chewed up. put a new balancer on and the car drove another 80k miles with a wobbly balancer and main pulley.

 

[Avery4]

that is crazy. if you have an old spare you should dissect it and post pics i'd love to see the contacts. i've never owned a honda but my wife did years ago, a 99 accord. it had all kinds of electrical gremlins. I wonder if hers had such a switch. but that car was terrible. one day the harmonic balancer fell off while she was driving. we were still dating and she called me and told me what the shop said. I refused to believe it until I saw it with my own eyes. turns out the crank was bent and that probably caused the bolt to work loose. I've never seen anything like it. end of the crank was all chewed up. put a new balancer on and the car drove another 80k miles with a wobbly balancer and main pulley.

That is one of the few parts I don't yet have an extra of. Her Accord could have had a bad ignition switch, a lot of older Hondas/Acuras had issues with them. I have seen the 6th gen and older ignition switches fail in a way that they no longer make proper contact and wiggling the key or twisting it back and forth the slightest amount makes or breaks contact. This was enough of an issue that there was a recall on a lot of older Honda models for the ignition switch failing prematurely and causing random stalling and/or no starts. The issues weren't exclusive to the recalled models though. But by the 7th generation, those issues seem to have been resolved since I have never seen or heard of any problems with those switches.

I wonder why Honda chose to build a heavy duty ignition switch and use such heavy gauge wiring instead of using relays. Maybe a cost issue, but I don't see how their approach could have saved much since so much heavy gauge wire was required. Maybe they were trying to eliminate the extra points of failure that additional relays introduce.

Honda recalls certain 1997 to 2000 Honda and Acura vehicles to replace ignition switches

Honda recalls certain 1997 to 2000 Honda and Acura vehicles to replace ignition switches

www.autoweek.com

 

[brianl703]

I have never seen, in any application including lawnmowers, an ignition switch powering anything more than a small light bulb or relay coil. and in many cases it powers a lower power relay that in turn powers the coil of a higher power relay. John Deere has a retrofit kit that does exactly that because the switch can't drive the starter relay coil.
https://www.greenpartstore.com/John-Deere-Starting-Improvement-Relay-Kit-AM107421.html

In many vehicles from the 80s and before, the ignition switch powered the blower fan directly, which is a fairly substantial load.

 

[eljefino]

In many 80s-90s vehicles (at least) the ignition switch has two "hot-in-run" outputs-- one for stuff needed during cranking, and one for stuff not needed like the blower fan. Remote start systems accommodate this.

Most of my keyed-ignition vehicles ran most-to-all of the need-it-to-run power through the switch directly. The exception are Dodges, they liked using an "auto shut down relay." It's the same exact part as the horn relay and a few others so you can switch them on the side of the road if you have problems. When the Toyota sudden accelleration drama came out I sat and mused as to why everything had to be logic-based, why couldn't you break the connection to fuel and/ or spark?

 

[Avery4]

In many vehicles from the 80s and before, the ignition switch powered the blower fan directly, which is a fairly substantial load.

Seems like that could be a problem, especially considering the high inrush current of motors starting up. Maybe that's where the myths about starting or stopping the engine with the AC and/or blower fan on came from in addition to the obvious draw on the battery.

 

[Avery4]

In many 80s-90s vehicles (at least) the ignition switch has two "hot-in-run" outputs-- one for stuff needed during cranking, and one for stuff not needed like the blower fan.

My Civics have that too. It automatically shuts off things like the blower fan and the radio while cranking, presumably to save battery power. Do modern cars not do that anymore?

 

[Jetronic]

My Civics have that too. It automatically shuts off things like the blower fan and the radio while cranking, presumably to save battery power. Do modern cars not do that anymore?

Depends, some turn off the headlights while cranking, but not if they are HID.

 

[madeej11]

Hi, I'm a complete novice with all this electronics stuff. My Toyota is wired so that the key must be in the accessory or start position to have power. I would like to wire it so the key is not needed. I'm presently using a 7 watt solar charger but I must run it directly to the battery using alligator clips, which is a real pain in cold or inclement weather. I don't have access to an outdoor power outlet so I had to buy a solar powered unit. The charger came with a plug to insert into the 12 volt cigarette lighter socket. Would you be able to instruct me as to how to wire or convert it to full time power on. Is there a simple conversion kit? Many thanks in advance for your time and help.

 

[wrcsixeight]

Hi, I'm a complete novice with all this electronics stuff. My Toyota is wired so that the key must be in the accessory or start position to have power. I would like to wire it so the key is not needed. I'm presently using a 7 watt solar charger but I must run it directly to the battery using alligator clips, which is a real pain in cold or inclement weather. I don't have access to an outdoor power outlet so I had to buy a solar powered unit. The charger came with a plug to insert into the 12 volt cigarette lighter socket. Would you be able to instruct me as to how to wire or convert it to full time power on. Is there a simple conversion kit? Many thanks in advance for your time and help.

A ciggy plug/receptacle is a pretty junky electrical connection. Even when working perfectly there is a significant amount of electrical resistance which will cause voltage drop, which, with battery charging, one would prefer to avoid.

An Always ON 12v power port, can be accomplished a few different ways.
One can find a 12v+ wire somewhere under the dash, tap into it, add a fuse and wire to the existing, or a new 12v receptacle. This can mean putting a digital multimeter probe through connectors or through wire insulation or on the back of the headlamp switch. ignition switch.

if one does not mind adding a new 12v receptacle, then consider that it is likely much better to NOT have to tap any existing wire, but run a new 10-2 wire through firewall, right to the battery, and fuse that at the battery. Use a rubber grommett through the firewall, and some split loom and zip ties underhood to keep it tidy and protected.

10 gauge wire with two conductors, directly from the battery to passenger compartment, can handle 30 amps. Far more than the 15 amps most 12v power port receptacles are rated for.

But with a low wattage solar panel, rated at say ~8 watts, which likely only can output 4 watts when under glass, one wishes to get all 4 potential watts, instead of 3.25 that one might only get if they use 18 awg wire, and 18 awg is likely what the stock 12v power port is wired with, from the fuse panel or however Toyota routes the power to your 12v powerport from the battery, which can mean many connections, each one of which adds its own resistance, and resistance is the enemy one is trying to minimize, when seeking effective battery charging through long circuits.

With no idea your skill set with a digital multimeter, or how your specific vehicle is wired, It is hard to steer you towards the best solution, as there are many different possibilities. If you are going to want to use an inverter to power 115v/ 230vAC household appliances, I'd recommend running new 10-2 wire right from battery through firewall, properly fused and protected from Chafing. I'd also recommend using not only a 12v powerport receptacle but have something like a 30 amp anderson powerpole connector, as ciggy plug and receptacles are not happy having to pass more than ~5 amps continuously, even if the wiring to and from this notoriously craptastic, yet ubiquitous 12v connection, is adequate for the load expected.

 

[madeej11]

A ciggy plug/receptacle is a pretty junky electrical connection. Even when working perfectly there is a significant amount of electrical resistance which will cause voltage drop, which, with battery charging, one would prefer to avoid.

An Always ON 12v power port, can be accomplished a few different ways.
One can find a 12v+ wire somewhere under the dash, tap into it, add a fuse and wire to the existing, or a new 12v receptacle. This can mean putting a digital multimeter probe through connectors or through wire insulation or on the back of the headlamp switch. ignition switch.

if one does not mind adding a new 12v receptacle, then consider that it is likely much better to NOT have to tap any existing wire, but run a new 10-2 wire through firewall, right to the battery, and fuse that at the battery. Use a rubber grommett through the firewall, and some split loom and zip ties underhood to keep it tidy and protected.

10 gauge wire with two conductors, directly from the battery to passenger compartment, can handle 30 amps. Far more than the 15 amps most 12v power port receptacles are rated for.

But with a low wattage solar panel, rated at say ~8 watts, which likely only can output 4 watts when under glass, one wishes to get all 4 potential watts, instead of 3.25 that one might only get if they use 18 awg wire, and 18 awg is likely what the stock 12v power port is wired with, from the fuse panel or however Toyota routes the power to your 12v powerport from the battery, which can mean many connections, each one of which adds its own resistance, and resistance is the enemy one is trying to minimize, when seeking effective battery charging through long circuits.

With no idea your skill set with a digital multimeter, or how your specific vehicle is wired, It is hard to steer you towards the best solution, as there are many different possibilities. If you are going to want to use an inverter to power 115v/ 230vAC household appliances, I'd recommend running new 10-2 wire right from battery through firewall, properly fused and protected from Chafing. I'd also recommend using not only a 12v powerport receptacle but have something like a 30 amp anderson powerpole connector, as ciggy plug and receptacles are not happy having to pass more than ~5 amps continuously, even if the wiring to and from this notoriously craptastic, yet ubiquitous 12v connection, is adequate for the load expected.

Thank you very much for your detailed response. I wasn't sure anyone would answer my question. I believe I will just continue with my present method which is probably the most efficient way to get the most power to the battery. The solutions you have suggested are probably out of my skill set.I do appreciate members like yourself who will take time from their day to help out less knowledgeable guys like myself. Thanks again. Cheers.