JRP3
Hyperactive Member
That sounds like what some people have reported when leaving a vehicle with low charge levels and coming back to find even less charge after a short time.
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Charging the Roadster
- Thread starter malcolm
- Start date
johnr
Member
I wonder if this is a characteristic of the batteries. My cell phone seems to do that sometimes. Lithium batteries are very temperamental, and it's also very difficult to accurately estimate charge level.
I could see that. In my experience, when you charge lithium batteries up to a high voltage level, as soon as you put them under load they fall to their nominal voltage and stay there for the duration of the discharge curve.
But at the end of the curve, it falls off of a cliff.
For our LiFePO4 batteries, the nominal voltage is 3.2 volts. You can charge them up to 3.6 volts easily, and 4.25 volts is the max. But it is largely a waste of time to charge them to 4.25 volts. It takes a lot of energy to get there and it is not really usable energy. It drops really quickly back down to the nominal at 3.2 volts under load.
The same at the bottom of the curve. Once you fall below the nominal, it can fall off of cliff quickly.
When an EV driver looks at a simply display showing "estimated range" or "state of charge" I can easily imagine how this voltage drop can be seen in terms of the remaining miles.
If you are at a full charge (range mode) it will easily discharge itself back to it's happy place of the nominal voltage or it max "comfort" voltage. For the roadster, max voltage is not a happy place. It doesn't want to be there. It wants to be at standard mode voltage.
I suspect a "distance to empty" gauge based primarily on pack voltage is not going to be accurate. It really needs to be more like weather prediction. Tracking historical data and looking at multiple inputs... Such as total power used since last recharge, and total power added if multiple partial charges were done. I suspect some systems need an occasional full drain and/or full charge to get their bearings again since lots of partial charges could possibly cause a slow drift in the range predictions.
Note, I have no idea what the Roadster does, or how accurate it really is. My point is that (as has been stated recently) the battery voltage drop is non-linear and not a reliable way to predict how much more charge you can get out of the pack. The voltage probably fluctuates with temperature and other factors as well.
In my RangerEV, I notice that the pack voltage doesn't directly correlate with the state of charge readings the computer is providing.
Another thing is that the pack characteristics change as it gets older.
So the algorithm to show range may need to take that into account as well.
Note, I have no idea what the Roadster does, or how accurate it really is. My point is that (as has been stated recently) the battery voltage drop is non-linear and not a reliable way to predict how much more charge you can get out of the pack. The voltage probably fluctuates with temperature and other factors as well.
In my RangerEV, I notice that the pack voltage doesn't directly correlate with the state of charge readings the computer is providing.
Another thing is that the pack characteristics change as it gets older.
So the algorithm to show range may need to take that into account as well.
JRP3
Hyperactive Member
I'm talking about a number of cases where people have had maybe 30 miles of range left showing on their meter, parked the vehicle, then returned a few hours later and the vehicle shows a lot less range or won't even move. Tesla should be keeping the pack high enough even in range mode to not allow discharge to go so low you can't move the vehicle, so I think something is draining the cells when parked.
According the the Martin Eberhard blog, the engine coolant pump consumes enough engery for a refrigerator. If you drive somewhere and leave a warm/hot battery, once you park the engine coolant pump will still be running. I am not sure if this would explain completely the situation you are describing.
I can't simply because I don't know what exactly happens. I was told by the Tech at Tesla in L.A. that some customers were having this problem with the MC120 after the GFCI tripped.
What is a better charge?
I joined the forum today and I have been reading about the unnecessary heat generated during high AMP charging such as the one created by the HPC (70A). Would it be better for the batteries to lower the charge rate to say 40A? Assuming that I can fit it within the Time-of-Use Window, I would love to use the most efficient way to charge the batteries at night.
Fred
I joined the forum today and I have been reading about the unnecessary heat generated during high AMP charging such as the one created by the HPC (70A). Would it be better for the batteries to lower the charge rate to say 40A? Assuming that I can fit it within the Time-of-Use Window, I would love to use the most efficient way to charge the batteries at night.
Fred
Rule of thumb, Charge as slow as you can get away with.
It does work out 40 amps is especially friendly to the batteries and a totally drained battery can be fully charged in the Time Of Use window.
Many owners passed on the HPC and are plenty happy.
It does work out 40 amps is especially friendly to the batteries and a totally drained battery can be fully charged in the Time Of Use window.
Many owners passed on the HPC and are plenty happy.
DrComputer
TeslaClubLA President
Take your MC 120 that is include with the Roadster, then upgrade it to a 240 volts / 40 amp mobile connector for $960.
http://www.evcomponents.com/ProductDetails.asp?ProductCode=RF40AMP
(disclosure, my company does the upgrade of the MC to a RFMC)
You can also get all of the adapters you would ever need in the wild.
14-50 in the middle of town....
Got an address? What is the breaker rating? I'd like to list this nifty location on EV Charger News
Got an address? What is the breaker rating? I'd like to list this nifty location on EV Charger News
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I was pulling the full 240 volts / 40 amps for two hours. It was clearly a 50 amp breaker. There were even more of them on the side of the post office building, but those are more difficult to reach.
Port Gamble WA Post Office
1 View Drive
Port Gamble, WA 98364
(the NEMA 14-50 is actually across the street)
We spoke with a county commissioner and the property owner about making an EV recharging parking spot with an EV sign. They have everything needed. Just need some paint and I offered to provide the sign.
EV parking signs
Thanks!
Signs are available from the Electric Auto Association. See
Electric Auto Association - Merchandise
-- the third item down. The extra-large size is the regular metal NO PARKING sign, normally pole-mounted.
Thanks!
Signs are available from the Electric Auto Association. See
Electric Auto Association - Merchandise
-- the third item down. The extra-large size is the regular metal NO PARKING sign, normally pole-mounted.
Tdave
Member
I've installed the TED 5000 meter on my 14-50 outlet in my garage. Last night was my first night of charging. Here's the graph of the power draw (in blue) and voltage (in red). I was pulling 40A.
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