Replacing the 12V aux Battery

[gregd]

So, I guess the charging behavior is different than on the Model S? I remember reading that the 12V battery charging on the Model S kicks in at some minimum voltage and then stops at some maximum voltage, and that voltage cycling repeats 4-5 times per day. Does the 12V battery not drain and recharge as often on the Roadster?

That's the fundamental question. I thought the answer was that both cars were very similar, that the car "runs" off the 12v battery when it's asleep, and recharges it as needed. Several of the posts in this thread say that's correct. My car, however, seems different.

I'm going to an event at the Rocklin SC tomorrow. If I can gently corner a Roadster tech, I'll ask.

 

[gregd]

That's the fundamental question. I thought the answer was that both cars were very similar, that the car "runs" off the 12v battery when it's asleep, and recharges it as needed. Several of the posts in this thread say that's correct. My car, however, seems different.

I'm going to an event at the Rocklin SC tomorrow. If I can gently corner a Roadster tech, I'll ask.

So, queue the theme music for "stump the band". I think I might be there on this one.

I talked to one of the ex-Roadster techs during the Rocklin event, and we kind of came up empty. He confirmed what we all understand, that on a 2.x car, when the car is asleep(i.e. not charging, not key-on), the only source of power to the car is the 12v battery. And a 12v lead acid battery under light load should settle at about 12-ish volts. Therefore, lacking a "champ battery" (his words), there is nothing to support the battery measuring 13.8 volts, or anything close to that, when the car is asleep.

He did say, however, that the source of the 13.8v is within the battery, i.e. that there is not an external 400v-to-12v converter like I was thinking. It's inside the battery and the battery management system therein, basically simulating the system of the 1.5 cars where the 12v is derived from the first two ESS battery sheets. So, apparently my car is subtly (but perhaps usefully) misbehaving in this regard, and is outputting 13.8-ish volts even when the car is otherwise asleep.

Next time I take the car in (presumably next spring for its annual leaf-and-debris-ectomy), they can take a closer look. Doesn't seem to be a problem, and keeping the 12v battery at about its float voltage is probably fine too. I say "about" because I don't know exactly what the voltage is, or what this type of battery wants. Blunt tools. But it's been this way at least since I got the battery replaced about 2 years ago (first time I measured it), so presumably if it was actually cooking the 12v battery, it would have done so by now.

 

[markwj]

I talked to one of the ex-Roadster techs during the Rocklin event, and we kind of came up empty. He confirmed what we all understand, that on a 2.x car, when the car is asleep(i.e. not charging, not key-on), the only source of power to the car is the 12v battery.

Yes, that is correct.

OVMS measures 12V voltage that powers it (from DIAG connector), and here is what it typically sees on my car:

2017-01-03 17:30:59.753245 +0800 rx msg D 128,0,1,43,30,23,8161,573084,63,0,22,2,120,120,13.1
2017-01-03 17:40:58.029154 +0800 rx msg D 128,0,1,40,48,24,8259,573184,69,0,23,2,119,119,13.1
2017-01-03 17:51:06.947751 +0800 rx msg D 128,32,1,45,66,25,8340,573263,40,0,20,2,118,118,13.1
2017-01-03 19:19:48.040153 +0800 rx msg D 96,8,4,35,47,26,8354,573279,0,5123,20,0,112,112,11.6
2017-01-03 19:57:59.702678 +0800 rx msg D 96,8,4,35,47,26,8354,573279,0,7397,20,0,114,114,11.6
2017-01-03 20:54:45.494514 +0800 rx msg D 96,8,4,35,47,26,8354,573279,0,10825,20,0,117,117,11.1
2017-01-03 21:26:35.284990 +0800 rx msg D 96,8,4,35,47,26,8354,573279,0,12711,20,0,115,115,11.6
2017-01-03 22:37:37.237899 +0800 rx msg D 96,8,4,35,47,26,8354,573279,0,16985,20,0,115,115,11.6
2017-01-03 23:05:20.033294 +0800 rx msg D 96,8,4,35,47,26,8354,573279,0,18663,20,0,120,120,11.6

First two records are the car driving. ESS is around 23C rising to 26C, and ambient temperature is 22C,23C,20C...

That "2" in the 12th column is what OVMS call 'car doors 3'. Bit #1 is the cooling pump indicator. During the drive it is on. As the drive ends it is on. A few hours later it is off. The car is sleeping.

The "13.1" in the 15th column is what OVMS sees as the 12V line powering it. It is not very accurate (based on a resistor network with 2x 1% tolerance). But, you can see in the fourth line that it drops from 13.1V to 11.6V. That is the switch from ESS DC-DC convertor to 12V battery.

It is pretty consistent: coolant pump on, 13.xV, coolant pump off, 11.xV.

 

[gregd]

It is pretty consistent: coolant pump on, 13.xV, coolant pump off, 11.xV.

...which is why my car is such a puzzle. Asleep or awake, 13.77 - 13.80 volts (maybe 20mv different).

Does anybody's Audio/Nav unit display anything other than 12.x (small x) volts? ("Disp" button on the JVC unit.) I know it taps into a different place in the 12v distribution network, but I've never seen it in the 13v range. Before my battery was replaced, it was indicating down in the 11.6v range, if I recall. Not below 12v now, so I guess my battery is still good.

 

[ML Auto]

11 days and finally just got power back--100+ gallons of propane later...

There is a standby 12V (probably 13.8V) power source from the ESS that is not connected to the 12V battery. It runs thru the small plug under the ESS disconnect. It mainly supplies the VMS and VDS-so they still function when you completely turn off the APS.

 

[hallvardr]

Shoai LFX09L2-BS12

Is you battery still working perfectly now?

I got the warning now, and my initial though was that I should just charge the one I have and put it back. On a gas car here in Norway it's recommended to charge them a couple of times a year to keep them healthy. Is there a reason the Roadster battery should be any different? (Should I choose the motorcycle icon on the charger when I charge it?)

If that does not work, where did you buy the Shorai?

 

[ShawnA]

Last fall I purchased the "Tesla Roadster Secondary Battery" from Gruber on eBay For about $53 which includes
US ground shipping.
It is a 12 Amp/Hour battery instead of the 8 Amp/Hour battery supplied with the car...
It is a bit smaller than the original battery. I installed it myself on its side.
I also attached a Battery Tender 0.8 Amp charger.
I threaded the charger cord through the front "grill." It is on a timer to charge 1 hour per day.
It has worked well so far.
I have to remember to unplug it before driving...

The roadster technical people I spoke with say that this battery only charges while the car is driven.
This is why I added the 1 hour per day trickle charger...

Shawn

 

[Stefan T]

I have bought a litium battery and shall replace mine old 12v battery with that

The new battery is a Shoai LFX09L2-BS12 (same as the uk guys one)
I cost me 1280Skr aprox $150 including shipping and 25% sales tax

I maybe will take some phots when i repace it but it won't befere the weekend

It's still working with out replacement

 

[hallvardr]

It's still working with out replacement

Awesome, do you remember where you got it?

 

[Stefan T]

Awesome, do you remember where you got it?

Not for the moment, but it was from some motorcycle parts dealers web page in sweden,

 

[n2mb_racing]

https://www.amazon.com/Shorai-LFX09L2-BS12-Extreme-Lithium-Powersports/dp/B005FIUGPQ

 

[hallvardr]

I have had my the main battery on the car on for a day now for the first time in a month. And when I came out this morning the 12v warning did not come up? Has the 12v battery been charged by the main battery the last day?

 

[hallvardr]

Not for the moment, but it was from some motorcycle parts dealers web page in sweden,

I saw you wrote that you got the same battery as Perrin, but he actually got one that was twice as big and with twice the capacity. I'm assuming you would still recommend the one you got since it has been fine for 3 years now?
Have you charged it at all in that time with a normal charger to top it opp, and can a normal charger do that on a battery like that?

 

[Stefan T]

I saw you wrote that you got the same battery as Perrin, but he actually got one that was twice as big and with twice the capacity. I'm assuming you would still recommend the one you got since it has been fine for 3 years now?
Have you charged it at all in that time with a normal charger to top it opp, and can a normal charger do that on a battery like that?

I done nothing with mine
Worked perfect, i have not charge it under the winter or somthing like that

 

[hallvardr]

My car has not been working the last 3 months. And when I got it working again I got a 12v battery warning. This warning went away the following day. So does the 12v battery get charged from the main battery?

I measured it and it was around 13v. Connected it to my "smart" charger and it finished charging it after 1 minute. So everything looks fine at least.

 

[ML Auto]

The 12V battery gets charged by the switchpack when the key is on. So if your car sat without being turned on for 3 months that would explain the warning. If there is a next time, charge the 12V battery before turning the car on, as charging a low battery can't be good for the expensive switchpack.

 

[smorgasbord]

OK, so my 2.5 is giving me the message saying the 12volt battery needs service.

I can get a YTX9-BS AGM battery very easily. What about lithium options - are they worthwhile?

Here's an Amazon query https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias=aps&field-keywords=ytx9-bs+lithium

Any suggestions from that list?

 

[X.l.r.8]

Seeing as people have had great success with the Shorai one, would it not be prudent to just use that one.

 

[n2mb_racing]

I'm still a little bit unclear on the lithium car batteries.... Do they have a balancing circuit or not? They seem to be 4S batteries that are constantly bulk charged / discharged. Once in a while the cells should be balanced. Unclear how the drop in replacements do that.

I might also be slightly concerned about a drop-in lithium ion battery, since the car will attempt to charge it at any temperature. Lithium ion batteries usually can't be charged below freezing without damage.

It seems like it could be done correctly, but I'm not sure if any of the drop-in replacements do all the right battery management things.

 

[X.l.r.8]

Shorai have a bms, as do Lithiumax, the other one referenced also had one but that was north of $500. As for the rest, I doubt it. My friend went to lithium in his motorcycle because he was tired replacing it every year. He researched and ended up with the same Shorai battery. Mostly because it was one of the few that had a BMS.