Old 1970s cottage, is 6 amps safe on an old 5-15?

[e-FTW]

(I've searched for an answer to this, to no avail. Feel free to link to something I might have missed.)

Rented a nice place in the woods on the north coast of California for a few days. Everything around here is old wooden cottages. Including the one we have for two nights. The birds are singing, the ocean rumbling in the distance, it is pretty awesome.

The garage has NEMA 5-15 outlets, you know standard 120 volt outlets, with a ground. Not a newer 5-20 (you know, the one with the notch in your bathroom) or anything better in sight. The place definitely dates from the 1970s or a bit earlier. From the lack of anything but 5-15 all over, and the look of the wall plates, electrical is from that vintage.
I want to get a trickle charge going, but I don't want to die a fiery death overnight by stressing an unknown and old electrical outlet, system and panel.

I've set the charge to be 6 of the 12 amps available.
What would yo do?

 

[boaterva]

They *should* be 15 Amps, which is 12, of course, continuous. I do get what you're saying. I'd do exactly what you're doing, try it at lower current, and see if the area around the socket heats up. And maybe ramp up to 12 if all is well. A good accessory for this (if you're going to do this often!) is one of the low-priced infrared temperature measuring guns. We have two we use for everything from cooking to room temps to this sort of thing.

The problem with 6 Amps is that you are barely compensating for normal losses, but I guess it's better than nothing!

 

[agloutney]

Before dialing it up to 12A maybe check if there are other loads on that same circuit and make sure they don't operate at the same time. If there's no other load and the wiring looks good there shouldn't be any issues.

 

[Rocky_H]

Yeah, it should be rated for 12, but you could probably do 9 or 10 with old wiring.

 

[brkaus]

It should be fine. I'm sure people run space heaters on it if it is a cabin. dial back to 10 if your concerned.

Also, watch the voltage drop on the screen as the current ramps up. If it stays pretty stable you should be safe.

And as others mentioned, check for heating around the outlet and at the breaker/fuse box if you know where it is located.

 

[ItsNotAboutTheMoney]

If 8A is good enough for GM's lawyers (see Chevrolet Volt),. you should be good with 8A on a typical installation.

 

[e-FTW]

If 8A is good enough for GM's lawyers (see Chevrolet Volt),. you should be good with 8A on a typical installation.

Missed that story...

 

[boaterva]

If 8A is good enough for GM's lawyers (see Chevrolet Volt),. you should be good with 8A on a typical installation.

Yeah, what was this, the only charging you'll ever need or something?

 

[scottm]

Does the dial even go as low as 6A...? Eesh that's a sad area of the dial I have never explored.

I'd dial it up from the lowest setting and watch what the voltage drop is doing on the console... if you bump up an Amp and it drops a volt or two... you got marginal wiring at the cottage. If it drops to 109V (I think...) the car will start backing down on the Amps by itself to try and raise the voltage. And if it can't hold at least 109V while charging it will stop altogether, regardless of what Amperage is dialed in. IIRC.. or maybe the cut off was 108. This happened at an old hotel where I had to scrounge for an outlet in the parking garage... I just gave up even trying to charge there.

 

[e-FTW]

Well, we lived! ;-)

Before and after posting this thread, and before going to bed, I had gone to check for heat around the outlet.
So thanks for confirming that.
I had done the same last year at another rental cottage, and definitely had felt heat from the outlet (the screws that hold the face plate carry heat real well to your finger for checking), but also from other outlets on the same circuit. Needless to say I had opted out of overnight charging that time. Sadly, I forget what amperage I ended using during the day.

Good point on space heaters, as there is no central heating in here, and I did see a small space heater in one of the rooms, plus the bathrooms have wall mounted space heaters (old ones with a fan in them, pretty sure those are on 120 v). Those would run for extended periods of time, the n part assuring that the outlets can support an extended load.

Lastly, the outlet in the garage is on what looks like a newer wall (unfinished sheet rock), and it is the only one on the property with a built-in breaker. Even the bathrooms don't have those.
So I feel pretty good.

 

[e-FTW]

Does the dial even go as low as 6A...? Eesh that's a sad area of the dial I have never explored.

I'd dial it up from the lowest setting and watch what the voltage drop is doing on the console... if you bump up an Amp and it drops a volt or two... you got marginal wiring at the cottage. If it drops to 109V (I think...) the car will start backing down on the Amps by itself to try and raise the voltage. And if it can't hold at least 109V while charging it will stop altogether, regardless of what Amperage is dialed in. IIRC.. or maybe the cut off was 108. This happened at an old hotel where I had to scrounge for an outlet in the parking garage... I just gave up even trying to charge there.

Good tip there by both you and brkaus! I did not know that.
The car is currently (no pun, I swear) happily drawing 121-122 volts at 6 amps, and did since last night.
I'll see if I ramp up slowly what the voltage changes are. I would like to get a better margin for y ride home, we want to check out Glass Beach before going up to Ukiah SC.

 

[brkaus]

Good tip there by both you and brkaus! I did not know that.
The car is currently (no pun, I swear) happily drawing 121-122 volts at 6 amps, and did since last night.
I'll see if I ramp up slowly what the voltage changes are. I would like to get a better margin for y ride home, we want to check out Glass Beach before going up to Ukiah SC.

The theory here is that when there is no load on the wiring, your reading the maximum voltage from the power supply.

As you pull more current, the voltage will drop based on the resistance in the wiring circuit (voltage = current * resistance). So, by watching the voltage on the car (at the load), your effectively watching the resistance in the circuit. If you see only a little drop, the wiring is likely adequate.

Similar to a garden hose when the faucet on the house is only open a tiny nit bit. If your not using the hose, you will have full pressure at the nozzle. But as soon you open the nozzle more, the pressure drop in the hose (or through the restricting partial faucet), showing how the flow is restricted. Of course, a hose is less likely to catch fire. But I guess if your circuit does catch fire, and not much is coming out of the hose, you will know where to look

Hope that made sense?

 

[gregd]

Lastly, the outlet in the garage is on what looks like a newer wall (unfinished sheet rock), and it is the only one on the property with a built-in breaker. Even the bathrooms don't have those.

I think what you mean is that the outlet is a GFI-type, with Test and Reset buttons. That would indicate that it's a more recent (more recent than 1970) addition, presumably up to more modern load standards. By code, the bathroom and kitchen outlets also must be GFI protected. Either they have another GFI outlet somewhere else in the house (or a GFI breaker in the panel) on a different circuit, or they are slaved off the GFI outlet you have in the garage, sharing the same breaker. Neither situation is particularly good or bad; just know what else is on the same circuit and be guided by that. That outlet is likely an addition to the house; see if you can figure out how hooked it in.

 

[e-FTW]

The theory here is that when there is no load on the wiring, your reading the maximum voltage from the power supply.

As you pull more current, the voltage will drop based on the resistance in the wiring circuit (voltage = current * resistance). So, by watching the voltage on the car (at the load), your effectively watching the resistance in the circuit. If you see only a little drop, the wiring is likely adequate.

Similar to a garden hose when the faucet on the house is only open a tiny nit bit. If your not using the hose, you will have full pressure at the nozzle. But as soon you open the nozzle more, the pressure drop in the hose (or through the restricting partial faucet), showing how the flow is restricted. Of course, a hose is less likely to catch fire. But I guess if your circuit does catch fire, and not much is coming out of the hose, you will know where to look

Hope that made sense?

Shame I cannot give it both informative ADN funny!

Yeah, it does make sense. Did a bit of testing: at 6 amps, it was solidly at 122 volts, with one blip at 123.
So I raised it 1 amp at a time, monitoring the voltage for 30 seconds at each step: from 7 to 9, it was showing a solid 122 volts, with blips in 121.
At 10 amps, which is where it sits now, it seems to have settled at 121 volts, with occasional life blips at 120.

 

[dhanson865]

Shame I cannot give it both informative ADN funny!

Yeah, it does make sense. Did a bit of testing: at 6 amps, it was solidly at 122 volts, with one blip at 123.
So I raised it 1 amp at a time, monitoring the voltage for 30 seconds at each step: from 7 to 9, it was showing a solid 122 volts, with blips in 121.
At 10 amps, which is where it sits now, it seems to have settled at 121 volts, with occasional life blips at 120.

The fact that it's offering 122volts at 6 amps says you have a good outlet/wiring/breaker. Probably good for more amps but so long as 10amps gets the job done I sure wouldn't turn it down any lower.

So long as the car is happy and the charging continues I wouldn't even flinch at a lower voltage if you bump it to 12 amps. Anything over 114volts is within specs.

 

[e-FTW]

The fact that it's offering 122volts at 6 amps says you have a good outlet/wiring/breaker. Probably good for more amps but so long as 10amps gets the job done I sure wouldn't turn it down any lower.

So long as the car is happy and the charging continues I wouldn't even flinch at a lower voltage if you bump it to 12 amps. Anything over 114volts is within specs.

That sounds good. After coming back from the beach, I set it to 12 to see what it would do: it is sitting at 120 volts, with a single blip at 119 volts.
I might scale back to 10 if I detect any heat around the outlet before bed time.

Feels like we have the basis of a how-to/best practice guide to old electrical systems here.

 

[e-FTW]

I think what you mean is that the outlet is a GFI-type, with Test and Reset buttons. That would indicate that it's a more recent (more recent than 1970) addition, presumably up to more modern load standards. By code, the bathroom and kitchen outlets also must be GFI protected. Either they have another GFI outlet somewhere else in the house (or a GFI breaker in the panel) on a different circuit, or they are slaved off the GFI outlet you have in the garage, sharing the same breaker. Neither situation is particularly good or bad; just know what else is on the same circuit and be guided by that. That outlet is likely an addition to the house; see if you can figure out how hooked it in.

The door to where the panel likely resides is locked, so cannot tell. It definitely is the only GFI outlet I have seen anywhere. Pretty sure nothing else is on that circuit, maybe the garage door opener. And that would only load the circuit for 5 seconds at a time.
And no, I do not know much about electrical systems (GFI does ring a bell). Am loving this education!

 

[e-FTW]

Just checked in on it: at 12 amps, the outlets felt a little warm. Scaled it back to 10 amps, and trust it will be fine.
Thanks for all the great info!

 

[gregd]

The door to where the panel likely resides is locked, so cannot tell. It definitely is the only GFI outlet I have seen anywhere. Pretty sure nothing else is on that circuit, maybe the garage door opener. And that would only load the circuit for 5 seconds at a time.
And no, I do not know much about electrical systems (GFI does ring a bell). Am loving this education!

GFI is "Ground Fault Interrupter". It's like a fuse or circuit breaker but instead of popping with too much current, it detects conditions where there is a current leak into ground (e.g. through somebody touching a live wire) and instantly breaks the circuit to prevent injury or death. Basically, the way it works is to watch how much juice is going out the Hot blade and making sure it all comes back on the Neutral. If there is the slightest imbalance, the missing juice must be going to (through) some place it doesn't belong, triggering the device to trip.

Code requires any outlet within some specified distance of anything wet (e.g. kitchen, bathroom, or outdoors / garage) to be protected. They do make special circuit breakers that go in the service panel, but they're expensive, so most of the time builders put special outlets in a bathroom that have the protection circuitry built in, and daisy-chain the other outlets off that first one. It's possible that they upgraded the house at some point to protect those outlets by putting the GFI outlet in the garage and feeding the others from there.

But it sounds like you've dialed in a workable solution. 10 amps should work. Enjoy your stay!

 

[brucet999]

The door to where the panel likely resides is locked, so cannot tell. It definitely is the only GFI outlet I have seen anywhere. Pretty sure nothing else is on that circuit, maybe the garage door opener. And that would only load the circuit for 5 seconds at a time.
And no, I do not know much about electrical systems (GFI does ring a bell). Am loving this education!

If you are curious about what else is on the circuit, you can get an idea by simply pressing the "test" button on that GFCI outlet in the garage, then see what other outlets have gone dead. That is not certain though, since downstream outlets that don't require GFCI protection could be wired off the "Line" terminal and so not be affected.