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Wall charge ranging from 2 - 4 mi /hr?

brjr

Member
Jul 16, 2020
77
9
worthington ohio
1. Why does the charge range/flicker between 2 - 4 miles per hour? Is it because of current throughout my home? I am using a standard 120 v wall socket for now. The Model 3 screen shows amp ranging from 9-2 / 12 amp.
2. I read somewhere that even replacing the wall socket with better hardware could help.
Occasionally the monitor says i have a bad extension cord (nope) or poor connection. Sometimes not usually. Why could that be?
3. Is it healthiest to charge the battery more often? Like every night?
 

KingBozo

Member
Oct 1, 2019
58
30
ABQ New Mexico
1. Why does the charge range/flicker between 2 - 4 miles per hour? Is it because of current throughout my home? I am using a standard 120 v wall socket for now. The Model 3 screen shows amp ranging from 9-2 / 12 amp.
2. I read somewhere that even replacing the wall socket with better hardware could help.
Occasionally the monitor says i have a bad extension cord (nope) or poor connection. Sometimes not usually. Why could that be?
3. Is it healthiest to charge the battery more often? Like every night?
That's pretty much what you're going to get off of 120v socket, you'll have to move up to a Nema-14-50 220v, standard electric dryer outlet.
 

camalaio

Active Member
May 28, 2019
1,483
2,095
Vernon, BC, Canada
Hmm. Do you mean it's dropping as far as 2A, or 9A? This would normally imply heat issues (usually due to bad connections, sometimes due to stuff being in direct sunlight). Is the outlet or plug adapter hot while charging?

If the screen is saying bad extension cord or connection, it's probably because it's detecting too large of a voltage drop? My own voltage varies a lot but I haven't seen that error before. This could be voltage fluctuation by the utility company (like in my case), within your home (e.g. if you have large electrical loads elsewhere), or simply the circuit powering the car. The last two cases shouldn't normally happen and could indicate something is physically wrong with your electrical.

Check what voltage it's reporting as well when charging (at both 12A and reduced amounts), but most importantly start taking steps to make sure your electrical in your house is safe.

---

The reason why the miles per hour changes so much is because it shows the rounded net power delivered, which follows approximately:
Rated Miles per Hour = (Voltage x Amps x 0.94) - 300​

And then divides it by a Wh/mi constant that the car is rated for (its efficiency) to represent it in miles per hour. Pulling a random one since I don't know what model you have, let's say that's 245Wh/mi

The 300W reduction is for overheads like running the coolant pumps, while the 0.94 is to reflect an approximately 94% efficient power conversion (which seems correct for my car over a range of charging setups).

So at 12A:
Rated MPH = 115*12*0.94 - 300 = about 997W or 4.07mph (would probably show as 4)​

And at 9A:
Rated MPH = 117*9*0.94 - 300 = about 690W or 2.82mph (would probably show as 3)​

I used a lower voltage for the higher current because voltage sag occurs. Note that while 9A is 25% less than 12A, the power going into the battery is actually about 31% less. This is mostly because at lower charging powers, that 300W overhead becomes a larger portion of the power going into the car.

Now, the same reason it varies by the current, it can also change on voltage. As above, it might be sensing too large of a voltage drop, which would also mean you are receiving low or variable voltage, which is probably swinging that miles per hour number down as well.

---

I'll try not to get too opinion-y here (neither mine nor others is going to be overly helpful in the end!), but as far as what's healthiest, just charge it every night assuming you use it most days and aren't charging over 90%. There is no health benefit to letting it drop to, say, 20%. But there is a potential negative impact on health, however small it may be.
 

RB88

Member
Mar 18, 2019
179
136
Seattle, WA
This isn't normal on 120v. Sometimes voltage may been seen to drop as low as 110v, but amperage shouldn't drop. It could be heat issues either due to old wiring, outlet or breaker. I would start with replacing the outlet, then the breaker (if you're comfortable doing that). I used to charge on 120v at a sustained 12A (or 16A on 20A breakers with the 5-20 adapter).
 

camalaio

Active Member
May 28, 2019
1,483
2,095
Vernon, BC, Canada
This isn't normal on 120v. Sometimes voltage may been seen to drop as low as 110v, but amperage shouldn't drop. It could be heat issues either due to old wiring, outlet or breaker. I would start with replacing the outlet, then the breaker (if you're comfortable doing that). I used to charge on 120v at a sustained 12A (or 16A on 20A breakers with the 5-20 adapter).

I used to charge solely off 120V as well, never had anything like this happen. This definitely isn't normal.

It's also very tolerant to utility voltage swings from what I can tell. Recently noticed 215V here, unloaded, on the "240V" setup we now have. Would've been 107V on the "120V". Voltage swings heavily here and never had an issue. So I really think there's a more local issue for sure.
 

SageBrush

REJECT Fascism
May 7, 2015
12,334
15,242
New Mexico
I would replace the socket (receptacle.) It sounds like you have poor contact with the plug.
And do yourself a favor after you have a new receptacle: when you pull the plug out, do so without any wiggling. Wiggling just bends the contacts inside the receptacle and leads to a poor connection with the plug.
 
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brjr

Member
Jul 16, 2020
77
9
worthington ohio
This isn't normal on 120v. Sometimes voltage may been seen to drop as low as 110v, but amperage shouldn't drop. It could be heat issues either due to old wiring, outlet or breaker. I would start with replacing the outlet, then the breaker (if you're comfortable doing that). I used to charge on 120v at a sustained 12A (or 16A on 20A breakers with the 5-20 adapter).
I will talk to an electrician. thanks
 

brjr

Member
Jul 16, 2020
77
9
worthington ohio
Hmm. Do you mean it's dropping as far as 2A, or 9A? This would normally imply heat issues (usually due to bad connections, sometimes due to stuff being in direct sunlight). Is the outlet or plug adapter hot while charging?

If the screen is saying bad extension cord or connection, it's probably because it's detecting too large of a voltage drop? My own voltage varies a lot but I haven't seen that error before. This could be voltage fluctuation by the utility company (like in my case), within your home (e.g. if you have large electrical loads elsewhere), or simply the circuit powering the car. The last two cases shouldn't normally happen and could indicate something is physically wrong with your electrical.

Check what voltage it's reporting as well when charging (at both 12A and reduced amounts), but most importantly start taking steps to make sure your electrical in your house is safe.

---

The reason why the miles per hour changes so much is because it shows the rounded net power delivered, which follows approximately:
Rated Miles per Hour = (Voltage x Amps x 0.94) - 300​

And then divides it by a Wh/mi constant that the car is rated for (its efficiency) to represent it in miles per hour. Pulling a random one since I don't know what model you have, let's say that's 245Wh/mi

The 300W reduction is for overheads like running the coolant pumps, while the 0.94 is to reflect an approximately 94% efficient power conversion (which seems correct for my car over a range of charging setups).

So at 12A:
Rated MPH = 115*12*0.94 - 300 = about 997W or 4.07mph (would probably show as 4)​

And at 9A:
Rated MPH = 117*9*0.94 - 300 = about 690W or 2.82mph (would probably show as 3)​

I used a lower voltage for the higher current because voltage sag occurs. Note that while 9A is 25% less than 12A, the power going into the battery is actually about 31% less. This is mostly because at lower charging powers, that 300W overhead becomes a larger portion of the power going into the car.

Now, the same reason it varies by the current, it can also change on voltage. As above, it might be sensing too large of a voltage drop, which would also mean you are receiving low or variable voltage, which is probably swinging that miles per hour number down as well.

---

I'll try not to get too opinion-y here (neither mine nor others is going to be overly helpful in the end!), but as far as what's healthiest, just charge it every night assuming you use it most days and aren't charging over 90%. There is no health benefit to letting it drop to, say, 20%. But there is a potential negative impact on health, however small it may be.

Yes the handle of the adapter is warm in the morning. If i could find a shorter corded adapter would that help?
I'll have an electrician look at it. I do have a degree in math but have turned very lazy in retirement. I will have to break down and study your formulas in the morning sometime before i start on the Scotch in the afternoon. Appreciate your information and formulas.
 

camalaio

Active Member
May 28, 2019
1,483
2,095
Vernon, BC, Canada
Yes the handle of the adapter is warm in the morning. If i could find a shorter corded adapter would that help?
I'll have an electrician look at it. I do have a degree in math but have turned very lazy in retirement. I will have to break down and study your formulas in the morning sometime before i start on the Scotch in the afternoon. Appreciate your information and formulas.

Heh, you can ignore the formulas really.

I find it weird the handle is warm, personally. On 120V 12A, mine was always basically the ambient temp. Even with 240V 24A, it's only very slightly warm (32A starts to get pretty warm).

From here I'm not sure what would help, but it's clear something isn't quite right.

Story time: At my first "career" job, our building had somewhat frequent brown-outs. Sometimes servers and computers would turn off, bit annoying. Relieving if your computer didn't, funny if your coworker's did. If I recall, at one point the power just completely died. Upon investigation, one of the main service feeds (I think it was a disconnect or something) had been arcing for years, and finally enough of it was smoked away. In a very old, very wooden building. Completely scorched inside. But all we noticed was a minor inconvenience with computers shutting off now and then!
 

brjr

Member
Jul 16, 2020
77
9
worthington ohio
Yes the handle of the adapter is warm in the morning. If i could find a shorter corded adapter would that help?
I'll have an electrician look at it. I do have a degree in math but have turned very lazy in retirement. I will have to break down and study your formulas in the morning sometime before i start on the Scotch in the afternoon. Appreciate your information and formulas.
 

brjr

Member
Jul 16, 2020
77
9
worthington ohio
Hmm. Do you mean it's dropping as far as 2A, or 9A? This would normally imply heat issues (usually due to bad connections, sometimes due to stuff being in direct sunlight). Is the outlet or plug adapter hot while charging?

If the screen is saying bad extension cord or connection, it's probably because it's detecting too large of a voltage drop? My own voltage varies a lot but I haven't seen that error before. This could be voltage fluctuation by the utility company (like in my case), within your home (e.g. if you have large electrical loads elsewhere), or simply the circuit powering the car. The last two cases shouldn't normally happen and could indicate something is physically wrong with your electrical.

Check what voltage it's reporting as well when charging (at both 12A and reduced amounts), but most importantly start taking steps to make sure your electrical in your house is safe.

---

The reason why the miles per hour changes so much is because it shows the rounded net power delivered, which follows approximately:
Rated Miles per Hour = (Voltage x Amps x 0.94) - 300​

And then divides it by a Wh/mi constant that the car is rated for (its efficiency) to represent it in miles per hour. Pulling a random one since I don't know what model you have, let's say that's 245Wh/mi

The 300W reduction is for overheads like running the coolant pumps, while the 0.94 is to reflect an approximately 94% efficient power conversion (which seems correct for my car over a range of charging setups).

So at 12A:
Rated MPH = 115*12*0.94 - 300 = about 997W or 4.07mph (would probably show as 4)​

And at 9A:
Rated MPH = 117*9*0.94 - 300 = about 690W or 2.82mph (would probably show as 3)​

I used a lower voltage for the higher current because voltage sag occurs. Note that while 9A is 25% less than 12A, the power going into the battery is actually about 31% less. This is mostly because at lower charging powers, that 300W overhead becomes a larger portion of the power going into the car.

Now, the same reason it varies by the current, it can also change on voltage. As above, it might be sensing too large of a voltage drop, which would also mean you are receiving low or variable voltage, which is probably swinging that miles per hour number down as well.

---

I'll try not to get too opinion-y here (neither mine nor others is going to be overly helpful in the end!), but as far as what's healthiest, just charge it every night assuming you use it most days and aren't charging over 90%. There is no health benefit to letting it drop to, say, 20%. But there is a potential negative impact on health, however small it may be.
In your equations for 12 and 9 amps how are you converting from W to MPH? I know the conversion factor is 1/244.9, but where is that stated and is that how the conversion is done? [email protected]/224.9 = 4.07. Is that right?
 

brkaus

Well-Known Member
Jul 8, 2014
7,742
6,274
Austin, TX
I have never seen more than 12/12 amps. Do other providers have greater service for standard `120 v outlets?
There is a standard 20a 120v outlet. With that outlet and the correct adapter it is possible to get 16a.

white-leviton-electrical-outlets-receptacles-m02-cbr20-wmp-64_1000.jpg
 
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scottwith1t

Member
Feb 24, 2020
44
34
Jacksonville
They would also need a 20 amp breaker and the appropriately sized wiring from the breaker to the outlet. I know that you already know this, but probably worth the reminder for those who don't. :)
also worth pointing out that its probably worth picking up a heavy duty outlet rather than using the garbage at the big box stores.

my $5 NEMA 6-20 outlet from the orange big box store got pretty damn warm and had a decent amount of voltage drop when charging, replaced with a $30 industrial outlet from Grainger electrical supply and now the plug is just slightly warmer than ambient with little to no voltage drop between the car and the electrical panel.

$5 big box store electrical outlets aren't designed for continuous duty.
 

brkaus

Well-Known Member
Jul 8, 2014
7,742
6,274
Austin, TX
They would also need a 20 amp breaker and the appropriately sized wiring from the breaker to the outlet. I know that you already know this, but probably worth the reminder for those who don't. :)

Yup. Exactly.

my picture was to help identify one in the wild. They sometimes exist in home garages and hotels.
 

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