12v battery time (sigh)

[gregd]

So now that the car is back on the road, the 12v battery seems to be done. I'm getting #428 alerts.

Since I don't have the ability to do this at home (no floor jack, and an aversion to the removal of wheels and such), I thought I'd look for perhaps an alternate solution. Hey, it worked for the PEM Fan connector, right?

When I last got the battery replaced in 2015, I had the technician connect a power pole connector up above, and wire (#12) it down to the battery terminals, so I could monitor things. So, perhaps I could add another 12 SLA battery up top? There's enough space that I could stuff a small one in there. It wouldn't last too long, but I could go through a dozen of them before matching the cost for Tesla Service to replace the one.

First, some monitoring, to see just how the car manages the battery.

As I've reported earlier, the car seems to keep the 12v battery at 13.77v constantly, whether the car is awake or asleep. Perhaps the alert is related to a transition in state? I put a meter on the PP plug, and watched as the car transitioned from sleep to awake. No change. Locked the car, let it sleep. No change. Unlock. Ha! The voltage took a large momentary dip, down below about 6 volts. That's what the #428 was complaining about.

So I grabbed a 12v 7AH SLA battery (the kind in a computer UPS), and affixed a power pole connector to it. Meter in line, attach to the car's battery through the aforementioned power pole. The meter is one of those digital units that reads voltage, power, and records peaks and averages. I note that the car charges at a several amps when it's a wake, and drops to a trickle charge when asleep, just enough to maintain the float. I unlocked the car, and in spite of the extra battery, I still got a #428. The meter reported a peak of 17.6 amps (!). Yikes! A cute little 2-ish AH SLA battery (what will fit in there) isn't going to supply that. Is that a real load (and, to what?), or is the car simply doing a battery load test (to annoy me)?

I might try a larger battery tomorrow, just to prove the concept, but wonder if anyone has any other thoughts. I really prefer not spending $500+ for just a battery swap, not to mention the hassle that is the hallmark of Roadster Service these days. I have ramps; can the 12v battery be accessed from under the car, without removing a wheel?

 

[hcsharp]

I have ramps; can the 12v battery be accessed from under the car, without removing a wheel?

In the time it took you to type that post, you could have removed the wheel with a $100 floor jack. Then you could have replaced the 12v battery in probably less time than it would have taken you to drive one-way to the service center.

You've done a great job of tackling some difficult problems with your Roadster. Out of everything you've done, this is by far the easiest issue to solve. It's cheaper to buy a floor jack than take someone to lunch here in the Roadster thread. Buy one and save your typing for a real problem. just sayin'.

edit: ok maybe i was rude... sorry. I assume you know I'm just yankin' your chain... your posts have been a great help to many of us... but I'm serious if you take me to lunch I'll give you one of the floor jacks rolling around my garage...

 

[jason.tv]

So now that the car is back on the road, the 12v battery seems to be done. I'm getting #428 alerts.

Since I don't have the ability to do this at home (no floor jack, and an aversion to the removal of wheels and such), I thought I'd look for perhaps an alternate solution. Hey, it worked for the PEM Fan connector, right?

When I last got the battery replaced in 2015, I had the technician connect a power pole connector up above, and wire (#12) it down to the battery terminals, so I could monitor things. So, perhaps I could add another 12 SLA battery up top? There's enough space that I could stuff a small one in there. It wouldn't last too long, but I could go through a dozen of them before matching the cost for Tesla Service to replace the one.

First, some monitoring, to see just how the car manages the battery.

As I've reported earlier, the car seems to keep the 12v battery at 13.77v constantly, whether the car is awake or asleep. Perhaps the alert is related to a transition in state? I put a meter on the PP plug, and watched as the car transitioned from sleep to awake. No change. Locked the car, let it sleep. No change. Unlock. Ha! The voltage took a large momentary dip, down below about 6 volts. That's what the #428 was complaining about.

So I grabbed a 12v 7AH SLA battery (the kind in a computer UPS), and affixed a power pole connector to it. Meter in line, attach to the car's battery through the aforementioned power pole. The meter is one of those digital units that reads voltage, power, and records peaks and averages. I note that the car charges at a several amps when it's a wake, and drops to a trickle charge when asleep, just enough to maintain the float. I unlocked the car, and in spite of the extra battery, I still got a #428. The meter reported a peak of 17.6 amps (!). Yikes! A cute little 2-ish AH SLA battery (what will fit in there) isn't going to supply that. Is that a real load (and, to what?), or is the car simply doing a battery load test (to annoy me)?

I might try a larger battery tomorrow, just to prove the concept, but wonder if anyone has any other thoughts. I really prefer not spending $500+ for just a battery swap, not to mention the hassle that is the hallmark of Roadster Service these days. I have ramps; can the 12v battery be accessed from under the car, without removing a wheel?

Find someone off the roadster group in your area that does garage calls or knows how to service lotus elise; Luckily someone found me on the group and it was the right person to have working on my car here in Florida.

He repainted my Battery bracket from corrosion in which Service center will not do things like these.

 

[gregd]

Find someone off the roadster group in your area that does garage calls or knows how to service lotus elise; Luckily someone found me on the group and it was the right person to have working on my car here in Florida.

He repainted my Battery bracket from corrosion in which Service center will not do things like these.

View attachment 609446 View attachment 609447

Hi Jason,

Thanks for the pictures. Question: Are the connections to the battery really just the push-on F-type? Those can't be robust enough for a 17 amp tug every time the car is unlocked. I wonder if they've simply become loose or corroded, given the discoveries at the other end of the car...

And, if so, I wonder how the service tech attached my power pole pigtail? I assumed they were screw-type, and they just wedged the wire under the nut.

It looks like I should be able to access the battery by removing the cover at the bottom of the car, at least enough to check the terminals.

 

[X.l.r.8]

I got the lithium battery, the terminals were exactly the same, the battery is 1/2 the size but comes with lots of insulation to protect it. Time was less than 30 minutes, it took longer to make my coffee that do the job. It’s well within anyone’s ability. I don’t remember if I took a wheel off, but I change my wheels almost monthly so quite possibly

 

[ML Auto]

An STX14L-BS is the cheap battery that fits. $40 on Ebay or $50 at Walmart. Jacking it up and removing the wheel is the hardest part.

 

[Bunnak]

An STX14L-BS is the cheap battery that fits. $40 on Ebay or $50 at Walmart. Jacking it up and removing the wheel is the hardest part.

Or when your car is at Gruber's getting other stuff done let him relocate it to the trunk(~$300). Then in the future you can change the battery in 2 minutes.

 

[gregd]

Or when your car is at Gruber's getting other stuff done let him relocate it to the trunk(~$300). Then in the future you can change the battery in 2 minutes.

Interesting idea, though I kind of like the trunk the way it is.

I've been side tracked with other things, but will get back to the battery problem tomorrow. The plan is to remove the panel on the bottom, and see if I can check the connections from there. But given the substantial current tug that I see when unlocking the car, and the size of the wires involved, and that pushing that current down from the power pole pigtail that I have isn't sufficient... the whole picture is just not making a lot of sense right now. More poking to do. It's intriguing that Gruber can put the battery so far away and not have the same problem with a voltage sag during Unlock, given that I essentially tried (and failed) the same thing with my power pole lash-up in the front. I must be missing something obvious.

Small challenge is that the car is too low in the front to clear the ramps that I have. Plan is to add some virgin fir or pine to the front of the ramps, to make the slope a bit more gentle.

 

[X.l.r.8]

The power for the door locks comes from the switchpack, the signal may generate from the 12v circuit at the battery but when I was looking at the schematics of the switchpack I saw the power locks connection. Maybe an OVMS poor gram we can chime in as that can control the power locks also.

 

[gregd]

The power for the door locks comes from the switchpack, the signal may generate from the 12v circuit at the battery but when I was looking at the schematics of the switchpack I saw the power locks connection. Maybe an OVMS poor gram we can chime in as that can control the power locks also.

The 17 amp tug on the battery is coincident with the push of the unlock button on my key, not the door latch. One thought is that the car is doing a couple of things at once here, waking up (so, cranking up the APS), and flashing the headlights. So perhaps the headlight flash is started before the APS is properly awake, causing the current tug? I should have some time today to do some more tests.

 

[jason.tv]

The 17 amp tug on the battery is coincident with the push of the unlock button on my key, not the door latch. One thought is that the car is doing a couple of things at once here, waking up (so, cranking up the APS), and flashing the headlights. So perhaps the headlight flash is started before the APS is properly awake, causing the current tug? I should have some time today to do some more tests.

you make everything so complicated; just change the battery..

 

[gregd]

you make everything so complicated; just change the battery..

Probably. But if I had done that with the PEM Fan connector, I would have missed the failed connectors down by the blower, and not have really solved the root problem. I'm seeing something here that's not making sense, so thought it would be a good idea to apply a similar approach.

 

[markwj]

One thought is that the car is doing a couple of things at once here, waking up (so, cranking up the APS), and flashing the headlights. So perhaps the headlight flash is started before the APS is properly awake, causing the current tug?

^ this

I suggest you try waking up first (open charge port door). Then try the door lock.

Only emergency systems are actually powered by that little 12v. Thinks like hazard warning lights. Brake lights. I am not sure if door locks would fall under that category, but it is likely. The immobiliser certainly is (powered by little 12v).

 

[gregd]

^ this

I suggest you try waking up first (open charge port door). Then try the door lock.

Only emergency systems are actually powered by that little 12v. Thinks like hazard warning lights. Brake lights. I am not sure if door locks would fall under that category, but it is likely. The immobiliser certainly is (powered by little 12v).

Hi Mark, that was exactly the next test I did. Interesting result. Still failed. In fact, the car doesn't even need to be locked. Doors open, car awake, little pump humming, all happy. Hit the Unlock button on the key, and the current tug still occurs! It's short, so the measurement changes from one test to the next, but I saw up to 19 A peak on one test. Bummer. That means that one can't work around the problem in the short term by simply waking the car up first before unlocking.

Good news (I think?) is that putting a fairly new 55AH SLA battery on the Power Pole was sufficient to prevent the #428's from occurring. So, it appears that the power pole and wires are in fact robust, and that a pair of my used 7AH bricks is simply too lame for this. I don't know if a new one (they were pulled from a UPS a few years ago) would be good enough, or if the surge is just too much for the smaller batteries. Might be interesting to try some, just to see what the requirements are.

So I think this means that I'm actually looking at an exhausted battery, not simply a loose contact or something more drastic (e.g. APS startup issue). Still a puzzle why the car would behave like this on a no-op unlock, but so be it.

Looking at the thread from Scotty2541 (Replacing the 12V aux Battery), his battery has screw terminals. Jason's picture showed F-type. I'm going to guess that the screw terminals are the original? If so, that would explain how the tech connected my wires in, answering that puzzle.

Time to dig into the car a bit deeper.

 

[X.l.r.8]

 

[eHorses]

Top is OEM and bottom is good alternative. Same size.

I recently installed lithium alternative from ohmmu..(I believe principle(s) of ohmmu is roadster tmc member also).
https://www.ohmmu.com/product-page/12v-lithium-battery-for-tesla-roadster

 

[gregd]

Thanks for the pictures and references. What amazes me is the (tiny) size of the battery. 8-9 AH. That's all?

I realized last night that I have another pair of 9 AH UPS batteries on the shelf, and tried hooking one of them to the Power Pole connector. The batteries have been sitting on the shelf for about 2 years, and for some reason, it's still fully charged. Seems to be working! No alert, though there was still a large drop in voltage, which is then (mostly) recharged after a few minutes. So, a solution within reach...

I'm thinking an important characteristic for the battery longevity is to get one with a CCA rating, which will cover that sharp 20 A "starting" surge better than one designed for a UPS where the draw is longer and lower. The OEM battery is, round numbers, 2x the cost of a 9AH SLA UPS battery. Will it last 2x longer in this application?

I'm really tempted to stuff one of the UPS units that I have into the space in front of the brake booster, on the driver's side. Looks like there's just enough space, and certainly easier for the wiring than, say, the trunk. Properly supporting it may be an issue; nothing to tie it to. But better approach is probably to just dig into the front fender. I think I have enough space to "do it properly" without removing the wheel, by turning it fully to the right. I may tackle this after Thanksgiving.

 

[jason.tv]

Grubers is 13Amps Led Acid; I would stick with that if you are not worried about money because it's $40-45 for shipping or something. This should provide a longer duration of cycles.

 

[markwj]

Are you sure that the old, dead, battery still being in the circuit is not affecting things? 16A for a couple of door solenoids seems ridiculous.

 

[slcasner]

I'm really tempted to stuff one of the UPS units that I have into the space in front of the brake booster, on the driver's side. Looks like there's just enough space, and certainly easier for the wiring than, say, the trunk. Properly supporting it may be an issue; nothing to tie it to.

You certainly would not want a heavy object in your car that is not securely mounted.