GM Volt Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
123 Posts
Discussion Starter · #1 ·
Based on the theory if I want to calculate how much electricity My Volt consume I multiply amps x Volt = kWr

So if I charge my car using the 8 amps I should consume (in theory) .960kWr at 12 amps I would be at 1.44 kWr

Now when I look at MYVolt.ca and I do some math I get 1.6 kWr per hour of charge. This is from mid-November to end of Feb.

I charge around 80% of the time at 8 amps.

Based on those figure I'm close to 50% efficiency as I charge more in 8 amps then in 12. I was expecting to be closer to 80% efficiency, seems I have a lots of 30% somewhere in the system. ( those are raw calculations but I feel it give a good portrait)

Any canadien living in Québec ( or anywhere else having the same conditions) could help me validate those numbers?

Car is park outside and is subject to mother nature.
 

·
Registered
Joined
·
1,060 Posts
I think the MyVolt stats are to be taken with a BIG grain of salt. I've seen some very questionable numbers lately, but that doesn't mean the car is doing anything wrong. I actually measured the exact amp draw at the circuit breaker panel with a high quality inductive clamp meter and found that the car draws the correct amount of energy within a tolerance of less than 3% under all different charging situations. I tested 120v @ 8 and 12 amps as well as 240v.
 

·
Moderator
Joined
·
8,680 Posts
I'm confused. If I'm following your math correctly, it seems to say that the battery is somehow absorbing 10% more power than the line is putting out at 12 amps! This is obviously impossible, and presumably suggests bad data.

Our general experience is that the charging process is about 80% efficient - 12.5-14 kWh from the wall to get a full 10-11kWh charge in the battery. 220V charging seems to be a little more efficient, most likely because it doesn't have to run the computers and coolant pumps for as long.

Note that the 80% number includes losses from the conversion from AC to DC, overhead from the ancillary systems, and conversion losses in the battery (and you're "paying" both electrical-chemical conversion losses and chemical-electrical conversion losses in the battery on the charging side, since we have no way (or reason) to model the chemical charge state independent of the energy we can get out as electricity.)
 

·
Registered
Joined
·
123 Posts
Discussion Starter · #5 · (Edited)
I'm confused. If I'm following your math correctly, it seems to say that the battery is somehow absorbing 10% more power than the line is putting out at 12 amps! This is obviously impossible, and presumably suggests bad data.

Our general experience is that the charging process is about 80% efficient - 12.5-14 kWh from the wall to get a full 10-11kWh charge in the battery. 220V charging seems to be a little more efficient, most likely because it doesn't have to run the computers and coolant pumps for as long.

Note that the 80% number includes losses from the conversion from AC to DC, overhead from the ancillary systems, and conversion losses in the battery (and you're "paying" both electrical-chemical conversion losses and chemical-electrical conversion losses in the battery on the charging side, since we have no way (or reason) to model the chemical charge state independent of the energy we can get out as electricity.)
Saghost

I know the data sound weird but I need to work with what Myvolt.ca gives me....Possible also my calculations are wrong this is why I wanted to check with other Volt owner having similar weather condition.

Worst case scenario I may have a faulty equipment not working properly that could explain the 10/30% difference


Here examples from past three months from MyVolt.ca

November (1/2 month)
85 hours 13 minutes 152 kW-hr 1.782 kWr/hr

December (full month)
162 hours 49 minutes 266 kW-hr 1.636 kWr/hr

January
143 hours 19 minutes 241 kW-hr 1.681 kWr/hr
 

·
Registered
Joined
·
3,454 Posts
Saghost

I know the data sound weird but I need to work with what Myvolt.ca gives me........
I measure and record every charge, using a Killawatt device, ( I know several of you have had these melt on you, I view this as a one day at a time activity...)

As a general rule, I have seen that, for my setup, it takes about 35% more power to charge the car at 12A, than it consumed on the previous drives, and that onstar underreports power used by about 6%. (this is too large to be just the losses in the EVSE and plugs and cables, so I call it "underreporting") As an example: if the car reports that I consumed 7.1 KWh on a drive, then the OnStar charge record will be 9.1 KWh and the Killawatt device will record 9.6 KWh. AS usual, there is variation with Temperature and with wall voltage (at home I see 120 volts while charging, at work about 116.).
BUT- onstar misses a lot of charging events and a lot of recharge power, so if you must know your power usage, it is better to keep a note book and write down your plug in time and charging rate.... or use the Killawatt device that has a memory, as I do....

Paul

yes, I know, this sort of record keeping is a sign of some sort of unmet emotional need... yadda yadda yadda- get over it... it gives my kids something else to laugh about....
 
1 - 6 of 6 Posts
Top