Leadership Team SLR No.77 Posted January 30, 2022 Leadership Team Share Posted January 30, 2022 When I bought my present car the battery isolator key switch was wired such that when "isolated" headlights were still live, the wiring had been substantially messed with prior to my ownership but I have heard of other cars with the same setup. Now corrected along with a whole load of other wiring issues.Even with the headlights not on there would clearly be a live supply under the dash area, if this was used for something such as a USB charge socket it could easily add enough load to drain the battery over a fairly short period. Also with an injection car my understanding is the ecu needs a minimum voltage of around 11v to actually wake up.Stu. Link to comment Share on other sites More sharing options...
John Vine Posted January 30, 2022 Share Posted January 30, 2022 Re #23:Well Jonathan, it was indeed a lovely sunny day, so I fired her up for a blat. Some voltage readings:On disconnection from the Accumate = 13.25v With ignition turned on = 12.25v During cranking (lasted just 2 secs or so) = 9.3vAre they reasonable values?JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 30, 2022 Member Share Posted January 30, 2022 "During cranking (lasted just 2 secs or so) = 9.3v"Thankyou, John.From what I can tell there's a risk of electronic components dropping out below 10.5 VIf there's no reason to think that that battery will ever improve then I'd replace it.JonathanPS: For anyone new to this... that measurement of minimum voltage while cranking is a convenient DIY load test for the battery. And those dropouts can mean that satisfactory cranking is not a good test of why a Seven isn't starting. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 30, 2022 Member Share Posted January 30, 2022 "During cranking (lasted just 2 secs or so) = 9.3v"How about repeating that test while the Seven is connected with fat jump leads to another vehicle running at 3,000 rpm?Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted January 30, 2022 Share Posted January 30, 2022 How about repeating that test while the Seven is connected with fat jump leads to another vehicle running at 3,000 rpm?I'm not sure what that would demonstrate. Can you elaborate, JK?Just to be clear...The car started within 2 secs of hitting the big red button. (Actually, Mrs V did this bit so that I could concentrate on the meter probes.) There was no hint of not wanting to start, but I agree that, given its age, a new battery would be a wise move.Can anyone confirm what the minimum voltage during cranking would be for an MBE 992? JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 30, 2022 Member Share Posted January 30, 2022 "How about repeating that test while the Seven is connected with fat jump leads to another vehicle running at 3,000 rpm?"..."I'm not sure what that would demonstrate. Can you elaborate, JK?"...My guess is that the minimum voltage would be much higher. If it isn't I'd like to know what's going on. And the logic of changing the battery in the Seven would be much weaker.Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted January 30, 2022 Share Posted January 30, 2022 Thanks, Jonathan. I'll try that next week. Or..... I could try with my NOCO booster hooked up. Would that be a valid test?JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 30, 2022 Member Share Posted January 30, 2022 Yes. Anything that would give more current when asked nicely.Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted January 30, 2022 Share Posted January 30, 2022 OK, I'll give it a whirl tomorrow.JV Link to comment Share on other sites More sharing options...
Ivaan Posted January 30, 2022 Share Posted January 30, 2022 To help find out what's causing the drain, keep repeating the test but pull out the fuses one at a time. Hopefully, you'll isolate the "bad" circuit. Link to comment Share on other sites More sharing options...
John Vine Posted January 31, 2022 Share Posted January 31, 2022 Re #33 + #34:Well, I repeated the test, this time with my NOCO attached. I also disconnected the inertia switch so as to extend the cranking. Result = 9.8v but fluctuating slightly. Trying again without the NOCO gave 9.3v (fluctuating) as before.I called SBD and mentioned the 9.3v. They were surprised the car even started, but did say that a digital multimeter wasn't the best tool for measuring this voltage accurately. They couldn't quote a general minimum value for the 992 as it would vary according to the vehicle and application.As a precaution, I'll be fitting a new battery shortly.JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 31, 2022 Member Share Posted January 31, 2022 Thankyou, John.Interesting comment from SBD on the starting!One of the issues with cheap digital multimeters is whether they can record and display transient voltages. For this sort of problem I think that they can. And the limited reports on those little meters that plug into cigar lighter sockets are also encouraging.But Andrew's analysis of the problem with Brise starters hinged on the recording of much briefer transients where an oscilloscope (including its modern incarnation) was essential.JonathanPS: Have you decided which battery will be in there next? Link to comment Share on other sites More sharing options...
John Vine Posted January 31, 2022 Share Posted January 31, 2022 It's not clear to me what the true significance of the 9.3v is here. As I said, the car starts within 2 seconds, although when the ambient temp is low (say 5C or less), the starter does churn a bit. During my testing today (in the comfort of the garage), it spun the engine ok (pretty much as normal, in fact). AFAIK, my DMM (Draper 41818) doesn't have a max/min voltage hold feature. I don't think there's a need for an oscilloscope (yet).I'll try jump leads from the tintop tomorrow and report back.Have you decided which battery will be in there next?Yes, another Banner. PS: We seem to have wandered a bit from parasitic drain. I hope the OP doesn't mind too much.JV Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2022 Share Posted February 1, 2022 Re #38:Hooked the battery up to Mrs V's Fiesta this morning, with revs at 2500.Voltage with the ignition on = 14v (presumably showing the Fiesta's charging rate?)With the inertia switch disconnected, cranking voltage = 11.6v. The engine was spinning fit to take off, but what does that say (if anything) about the state of my battery?JV Link to comment Share on other sites More sharing options...
ChrisC Posted February 1, 2022 Share Posted February 1, 2022 The real question is what are you going to do when you find the drain on a 7. It's not as if the drain will be caused by a can bus signal waking up modules, the 7s electrical design is just not that complicated. The ECU and immobiliser are permanently powered by design, if you have a upright dash then I bet that module is also powered permanently. Beyond that is simple switch and device electrics. All this means is the draw (assuming nothing if faulty) can't be changed without wiring loom redesigns. Link to comment Share on other sites More sharing options...
SM25T Posted February 1, 2022 Share Posted February 1, 2022 Disconnect the battery with a cut off switch. Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2022 Share Posted February 1, 2022 #41: Agreed. But did we ever resolve the mystery drain in #7?JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2022 Member Share Posted February 1, 2022 "The real question is what are you going to do when you find the drain on a 7."Yes, great question.A few suggestions:1 Gain a better understanding of what's happening and why there are such different reports.2 Know more about who would be wise to fit a battery isolator (as above). 3 Adopt a smarter charging strategy. 4 Fit a more suitable battery."All this means is the draw (assuming nothing if faulty) can't be changed without wiring loom redesigns. "5 We might be able to try some quite simple improvements. As with the MFRU and cooling systems. And that might avoid some battery replacements."The ECU and immobiliser are permanently powered by design... "I wouldn't assume that on the goulash that is a Seven. : - )Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2022 Member Share Posted February 1, 2022 "Hooked the battery up to Mrs V's Fiesta this morning, with revs at 2500.Voltage with the ignition on = 14v (presumably showing the Fiesta's charging rate?)With the inertia switch disconnected, cranking voltage = 11.6v. The engine was spinning fit to take off, but what does that say (if anything) about the state of my battery?"Mmmmmm... data! Thankyou very much.First thoughts:1 A better battery is going to lift that minimum voltage during cranking.2 It's cranking (and starting) at the moment and not noticeably slowly. But more oomph made it crank much faster. So cranking and starting is not a good test of the state of the battery. (But it's the one that most of us use most of the time.)(3 That jump starter pack doesn't deliver anything like as much oomph as the Fiesta.)Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2022 Share Posted February 1, 2022 Thanks, Jonathan.A better battery...Do you mean a new Banner or a different make?JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2022 Member Share Posted February 1, 2022 I only meant better than what you have in there at the moment... and that could include a new Banner... ... but always happy to discuss the best battery! : - )Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2022 Share Posted February 1, 2022 Thanks, Jonathan.JV Link to comment Share on other sites More sharing options...
ChrisC Posted February 1, 2022 Share Posted February 1, 2022 Maybe I should be more specific, the ECU and immobiliser have been permanently powered on my Sigma (circa 2015) and both my Duratecs (2016 & 2019). None of my cars had the high end dash, so never had a full fat dash control module, but my 2019 has the £35 version dash control module, which I assume is nothing more that a connection block for that price. agree with the goulash, or as I would put it "old school". Which in a way is still better than having a BCM and computers everywhere. Link to comment Share on other sites More sharing options...
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