WattsLeft™ Monitor (Parallax SX28AC/DP SOC/CAN Project)

[tbleakne]

A couple of questions about your impressive product. From pg 9 Quick Guide, am I correct to assume that SOC in upper left corner of screen 1 is the State of Charge % relative to the current battery capacity, and not Gids/281?

I have become very comfortable with % = Gids/281 on my original Gid meter, now 1.5 years old. I call this value Gid% to distinguish it from the first definition. With my driving, 1 mile is very close to 1% Gid%, and I can apply corrections based upon upcoming elevation changes to estimate my margin at my destination. This relationship doesn't change as my battery loses capacity.

Since you have access to the Gid values with WattsLeft, unlike the current ELM287, would you consider adding an option to display Gid% instead of SOC on Screen 1?

[Turbo3]

WattsLeft SOC% is gids/281.

[TonyWilliams]

WattsLeft SOC% is gids/281.

Ok, then my request would be to rename this to Gid% instead of SOC%.

[Turbo3]

In the WattsLeft world there are only Gids so 100% 'SOC' =281 Gids.

When you sell a product to the general public you have to keep it as simple as possible.

There are no 'SOC' labels on the display anyway so nothing to change there, just xx.x%.

Just look at all the discussion going on about AHr, SOC, gids. I don't want to get into all that.

When you hit a certain gid level the car gives you a low battery warning or very low battery warning. So the amount of Gids you have left is of some importance to the car and should be to the driver.

[Luft]

How many gids per KWh?

A new fully charged battery pack holds 281 gids. Does that represent the usable 21 KWh or the maximum 24 KWh?

I'm thinking that the 281 number is based off of the usable KWh in a fresh fully charged pack which would make it about 13.4 gids per KWh but I want to be sure.

Thanks.

[TonyWilliams]

How many gids per KWh?

A new fully charged battery pack holds 281 gids. Does that represent the usable 21 KWh or the maximum 24 KWh?

I'm thinking that the 281 number is based off of the usable KWh in a fresh fully charged pack which would make it about 13.4 gids per KWh but I want to be sure.

Thanks.

300 Gids represents 24kwh, since each Gid unit is 80 wattHours stored. When you consume those Gids, the value is about 76 wattHours each. That 76 value per Gid will decrease with temperature below 70F degrees, plus the sensors themselves have a hard time being accurate with temperature change. In addition, the total quantity of Gids at a full charge will decrease with degradation over time, cycles, exposure to heat, depth of discharge, time left at high states of charge, etc.

281 Gids is a fully charged, new condition LEAF battery, or about 22.48kWh stored. When that is consumed, there would be about 21.4kWh to be burnt to a completely dead battery, however, approximately 400 wattHours are not available to be burned at the bottom to prevent "bricking" the battery. That leaves 21kWh burned for about 281 Gids minus about 5 Gid at battery low energy cutoff.

281 - 5 = 276 Gid available * 76 wattHour each = 20.976kWh available to you. All this assumes new condition battery at 70F degrees. Again, a colder battery will have less available energy, and a degraded battery will be reflected with lower than 281 Gid at full charge.

There is no magic bullet of Gid = X kWh, however 276 Gid / 21kwh available = 13.14 Gid per kWh at 70F.

[Luft]

How many gids per KWh?

A new fully charged battery pack holds 281 gids. Does that represent the usable 21 KWh or the maximum 24 KWh?

I'm thinking that the 281 number is based off of the usable KWh in a fresh fully charged pack which would make it about 13.4 gids per KWh but I want to be sure.

Thanks.

300 Gids represents 24kwh, since each Gid unit is 80 wattHours stored. When you consume those Gids, the value is about 76 wattHours each. That 76 value per Gid will decrease with temperature below 70F degrees, plus the sensors themselves have a hard time being accurate with temperature change. In addition, the total quantity of Gids at a full charge will decrease with degradation over time, cycles, exposure to heat, depth of discharge, time left at high states of charge, etc.

281 Gids is a fully charged, new condition LEAF battery, or about 22.48kWh stored. When that is consumed, there would be about 21.4kWh to be burnt to a completely dead battery, however, approximately 400 wattHours are not available to be burned at the bottom to prevent "bricking" the battery. That leaves 21kWh burned for about 281 Gids minus about 5 Gid at battery low energy cutoff.

281 - 5 = 276 Gid available * 76 wattHour each = 20.976kWh available to you. All this assumes new condition battery at 70F degrees. Again, a colder battery will have less available energy, and a degraded battery will be reflected with lower than 281 Gid at full charge.

There is no magic bullet of Gid = X kWh, however 276 Gid / 21kwh available = 13.14 Gid per kWh at 70F.

Thanks Tony, that's very helpful.

[surfingslovak]

When you hit a certain gid level the car gives you a low battery warning or very low battery warning. So the amount of Gids you have left is of some importance to the car and should be to the driver.

Jim, I really appreciate all the work that has gone into WattLeft and the ELM327 project, and I don't want to open another unnecessary discussion, since I know how hard it is to get consensus here. It took a lot of effort to get an agreement on 21 kWh usable and on 24 kWh rated capacity a while back, for example. There will always be folks with some kind of bias or a personal opinion. It's just the way it is with these things. That said, Nissan has not indexed the instruments in the LEAF to some imaginary values. No, they have been calibrated to certain levels of stored energy.

Take the low battery warning, for example. It comes up at 4 kWh stored energy remaining, which is a constant and does not change over time as the battery degrades. The very low battery warning comes up at 2 kW stored energy remaining. This is not just my opinion, these design decisions are a matter of public record. Since we are essentially reverse engineering the car, it takes effort and sometimes even faith to bridge the gaps in our understanding. Gids are units of stored energy, and not SOC, as was originally assumed. They represent watt-hours and kilowatt-hours, which are universally understood as units of energy.

WattsLeaf is an excellent product, and you might not want to redesign it. That said, before the next revision of the LEAF platform and before a different battery pack is released, it would be good to agree that it's beneficial to find a way to express stored energy in universal units of measure. It won't help matters if a certain group of LEAF owners was looking at raw CAN bus values, which meant one thing, and another group of owners would use something different, because their LEAF had a new battery pack and new software.

Going from an old LEAF to a new LEAF would be a big transition, since these aftermarket devices would use different raw values from the CAN bus. If kilowatt-hours were used, then the transition would be seamless. Besides, isn't one of the goals that Nissan should show kWh directly on the dash? It would be good if the strong engineering community we have here set the right tone at some point in the not-too-distant future, and demonstrated that this approach can work.

[lion]

Do you have any yellow OLED units left? Is the firmware field upgradable? Have you ever considered installing a rechargeable battery to prevent data loss in case of 12V battery failure (or someone unplugging it)?

The yellow OLED screens look amazing.

[Turbo3]

From the last production run I have three of the Yellow WattsLefts remaining. However, I have two on hold that are just awaiting PayPal payment before I ship them which should happen on Monday. So that leaves just one Yellow OLED unit remaining.

I will start another build the middle of June and all those will have the option of the Yellow OLED display. There is also one base Blue LCD without Bluetooth available.

The firmware is upgradable but it requires a special adapter ($60+) so the unit would need to be shipped back to me if I ever come up with newer firmware (no plans at this time). Shipping would be around $5 and I would ship the unit back free.

I have thought about a supercap but that is about it.

With the bluetooth option the history data can be externally saved with an Android app I am working on. There is a test version of the app that just displays the history data on the android device but does not currently save it. When finished it would merge the history data into a CSV file.

Yes the OLED display is very nice.