Longer term Ohmmu experiences?

[Rottenapplr]

If you get three years of reliable operation from the OEM LA battery without any codes, you're an outlier on the end of the curve. 2 years looks more possible. 12-18 months, probable. By those numbers your approach does not look like it saves any money at all over an aftermarket battery that admittedly requires jiggering and resets but that lasts 4-5 years.

Fine change it every 18 months lol. still cheaper that the lithium aftermarket battery. Ohmmu is $478 w/ shipping.

Three OEM battery changes is $333 over 5 years if replaced every 18 months lol. And You are not the one doing the battery replacement. If you want to be a risk taker and live on the wild side, change it every 24 months!

 

[dfwatt]

Fine change it every 18 months lol. still cheaper that the lithium aftermarket battery. Ohmmu is $478 w/ shipping.

Three OEM battery changes is $333 over 5 years if replaced every 18 months lol. And You are not the one doing the battery replacement. If you want to be a risk taker and live on the wild side, change it every 24 months!

Tesla quoted us $148 here to replace the battery not sure where you're getting your numbers from?

 

[Rottenapplr]

Tesla quoted us $148 here to replace the battery not sure where you're getting your numbers from?

Socal.

 

[AlanSubie4Life]

Tesla quoted us $148 here to replace the battery not sure where you're getting your numbers from?

It used to be $85 for 12V ( no idea if has increased in past year). Makes sense to quote uninstalled price unless you plan to have someone install the Ohmmu for you.

I think 12V probably last a little longer than they used to because Tesla may have reduced the actual sleep drain a little at some point.

Mine lasted 3.5 years and I know several people going on 4.5 years. Of course there are counter examples. Maybe there were some bad batches too.

But these days three years seems safe most of the time.

I did spend some money to ensure I have a backup plan to avoid inconvenience in case of failure. Maybe another $100 or so.

 

[dfwatt]

It used to be $85 for 12V ( no idea if has increased in past year). Makes sense to quote uninstalled price unless you plan to have someone install the Ohmmu for you.

I think 12V probably last a little longer than they used to because Tesla may have reduced the actual sleep drain a little at some point.

Mine lasted 3.5 years and I know several people going on 4.5 years. Of course there are counter examples. Maybe there were some bad batches too.

But these days three years seems safe most of the time.

I did spend some money to ensure I have a backup plan to avoid inconvenience in case of failure. Maybe another $100 or so.

What's interesting in all these finally nuanced analyzes about cost is the failure to include the 15% differential 'round trip efficiency' of lithium ion phosphate versus lead acid that means essentially that roughly 15% of every kilowatt hour that goes in or out of the 12 volt system is saved by the better chemistry. Without knowing what the total load on the low voltage subsystem is it's hard to calculate that but I would bet it's low hundreds of kilowatt hrs at least over the four year to five year span that we're talking about. Whether that's worth the grief of occasional resets is another matter. For me it is but for somebody else it might not be. Then there's the weight savings. Ditto on that question as well.

 

[Flybyglass]

What's interesting in all these finally nuanced analyzes about cost is the failure to include the 15% differential 'round trip efficiency' of lithium ion phosphate versus lead acid that means essentially that roughly 15% of every kilowatt hour that goes in or out of the 12 volt system is saved by the better chemistry. Without knowing what the total load on the low voltage subsystem is it's hard to calculate that but I would bet it's hundreds of kilowatt hrs or over the four year to five year span that we're talking about. Whether that's worth the grief of occasional resets is another matter. For me it is but for somebody else it might not be. Then there's the weight savings. Ditto on that question as well.

It appears Ohmmu may have a solution coming. From Support:

1. We have identified the issues causing these errors.
2. Ohmmu is currently developing a hardware revision (Rev4+) to resolve this issue for existing customers, which should be available at the end of June 2023.

This should be in the form of a software update via the Ohmmu app for V4+ users. The app is undergoing revision to allow updating the battery and data collection of any issues if needed. My issue occurred at low temperatures the battery would not charge with low (1 amp or less) charging. Higher amps at low temperatures (6 amps) no problem. When the temperature dropped (near freezing) the car normally trickles at .1 amps or less (as seen on the LV battery page in service mode). No charge accepted causes the error chain.

 

[AlanSubie4Life]

it's hard to calculate that but I would bet it's low hundreds of kilowatt hrs at least over the four year to five year span that we're talking about.

This is actually not that hard to estimate. The standby drain is around 7W for Model 3. (Call it 10W.) This results in 1 mile per day or so of phantom drain due to sleep - we don’t care about other sources; they do not come from the 12V.

So assuming all the time is spent in sleep (not true since it has to wake up), that is 88kWh per year. That all has to come from the 12V.

15% of that is 13kWh of savings per year.

At my rates of 16 cents per kWh (night rate) that is $2 per year savings.


Call it $5 per year to be safe.

 

[dfwatt]

This is actually not that hard to estimate. The standby drain is around 7W for Model 3. (Call it 10W.) This results in 1 mile per day or so of phantom drain due to sleep - we don’t care about other sources; they do not come from the 12V.

So assuming all the time is spent in sleep (not true since it has to wake up), that is 88kWh per year. That all has to come from the 12V.

15% of that is 13kWh of savings per year.

At my rates of 16 cents per kWh (night rate) that is $2 per year savings.


Call it $5 per year to be safe.

What about loads on the 12 volt system while you're actually driving? You're assuming those are zero? Everything except the AC is powered from the 12 volt system as I understand it.

 

[AlanSubie4Life]

What about loads on the 12 volt system while you're actually driving? You're assuming those are zero? Everything except the AC is powered from the 12 volt system as I understand it.

No, that is not correct. The 12V is floated (unless it is being charged) while driving.

The 12V system is driven by the DC-DC (which has a few kW of output capacity), which is floating the 12V, as I understand it.

You can drive with a 12V missing apparently (it warns you that it is missing the 12V - note I have not tried this myself, so not sure the veracity, but multiple people have mentioned it).

 

[Flybyglass]

What about loads on the 12 volt system while you're actually driving? You're assuming those are zero? Everything except the AC is powered from the 12 volt system as I understand it.

With the Ohmmu app, you can see the LV battery loads. They are near zero with the 12 volt needed being supplied from the HV battery through converters. The LV battery would be primarily used for wake up.

 

[AlanSubie4Life]

I feel like the Ohmmu battery would be well worth the price if it could give warning-free operation for more than 10 years. There is value in having no worries about the 12V at all, if that were realizable, in all weather conditions. But this thread makes it sound painful.

 

[dfwatt]

No, that is not correct. The 12V is floated (unless it is being charged) while driving.

The 12V system is driven by the DC-DC (which has a few kW of output capacity), which is floating the 12V, as I understand it.

You can drive with a 12V missing apparently (it warns you that it is missing the 12V - note I have not tried this myself, so not sure the veracity, but multiple people have mentioned it).

With the Ohmmu app, you can see the LV battery loads. They are near zero with the 12 volt needed being supplied from the HV battery through converters. The LV battery would be primarily used for wake up.

When I get my new one I'll be curious to see because it's hard to believe that the 12 volt battery does literally nothing except when the vehicle is sitting. I'm sure it puts something out from time to time and then gets charged particularly if you've got near instantaneous loads from the audio system which can draw a lot of current to supply the subwoofer amp

 

[Flybyglass]

When I get my new one I'll be curious to see because it's hard to believe that the 12 volt battery does literally nothing except when the vehicle is sitting. I'm sure it puts something out from time to time and then gets charged particularly if you've got near instantaneous loads from the audio system which can draw a lot of current to supply the subwoofer amp

I will qualify my statement. I haven't observed any significant amounts draw (more than 1 amp) after the car is awake. It also draws upon wakeup to charge.

 

[dfwatt]

I will qualify my statement. I haven't observed any significant amounts draw (more than 1 amp) after the car is awake. It also draws upon wakeup to charge.

How does the DC to DC Bridge allow for the rapid demands for high current for example from the audio system? I don't understand that? Wouldn't that system be too slow?

 

[AlanSubie4Life]

When I get my new one I'll be curious to see because it's hard to believe that the 12 volt battery does literally nothing except when the vehicle is sitting. I'm sure it puts something out from time to time and then gets charged particularly if you've got near instantaneous loads from the audio system which can draw a lot of current to supply the subwoofer amp

The charging voltage is about 14.4V. The float is 13.5V. The undriven full charge is about 12.8V.

If the DC-DC sags over 0.5V, or as much as 1V, it would seem there would be an issue with the DC-DC robustness. Maybe it does, but seems like a bad design because it would rely on the 12V to function.

The 12V cannot supply current above somewhere between 12.8V and 13.5V, I don’t think.

 

[voltaholic]

"It appears Ohmmu may have a solution coming. From Support:

1. We have identified the issues causing these errors.
2. Ohmmu is currently developing a hardware revision (Rev4+) to resolve this issue for existing customers, which should be available at the end of June 2023.

This should be in the form of a software update via the Ohmmu app for V4+ users. "

How can a ' hardware revision ' be in the form of a software update ???

 

[Flybyglass]

"It appears Ohmmu may have a solution coming. From Support:

1. We have identified the issues causing these errors.
2. Ohmmu is currently developing a hardware revision (Rev4+) to resolve this issue for existing customers, which should be available at the end of June 2023.

This should be in the form of a software update via the Ohmmu app for V4+ users. "

How can a ' hardware revision ' be in the form of a software update ???

"It appears Ohmmu may have a solution coming. From Support:

1. We have identified the issues causing these errors.
2. Ohmmu is currently developing a hardware revision (Rev4+) to resolve this issue for existing customers, which should be available at the end of June 2023.

That quote is from the quote is from the web site. The quote:
This should be in the form of a software update via the Ohmmu app for V4+ users. "
Is my interpretation since the battery is again for sale and the revision for existing owners of V4+ appears to be timed with the app revision that will allow software updates to the BMS. Since the battery is for sale and no swap program is mentioned my conclusion is the software update that Ohmmu has talked about so often. I have made several inquiries about new hardware needed with no answer.

 

[Perscitus]

Any news from Sean re the Ohmmu app, firmware update? I have not hears anything but the Apr to Jun 2023 edit above is the second delay this year.

 

[(@r8[]np4nd4]

Looks like Sean doesn't respond to emails anymore.

 

[dfwatt]

Looks like Sean doesn't respond to emails anymore.

I suspect they are hanging on by their fingernails and trying to get this last revision tuned up so that they can actually sell something that does not require regular resets. If they can't do that then obviously they can no longer sell to Tesla Model 3/Y owners. For sure one of their biggest markets. They have tried to segue into other directions but we'll have to see if version 4 plus actually works.