Smegnoguk Posted March 29, 2014 Share Posted March 29, 2014 Help! 😳 My son's car. Battery went flat so I charged it up. Went flat again after 3 days so I replaced it with a new one from Halfords. Also went flat. Have read that circuits can jam on even when all is switched off an drain battery. Have charged battery again and tested all fuse tops with a multimeter to see if there is a voltage across any of them but no luck. If I switch meter to amps and put it in series with the negative terminal on 250 milliamps there is a strong reading off the scale. Does that mean there is a current flowing when there shouldn't be? Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted March 29, 2014 Share Posted March 29, 2014 Yes. When you say it goes off the scale ...... you need to choose another scale ...... so you know the real current draw. Go for 1A or 10A scale ? Anything over a few milliamps will drain the battery. Some cars suffer boot light or self-dimming interior lights not shutting down fully. Switch these off or take bulb out of boot light. Then measure again. Could anything be left turned on ?? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 29, 2014 Member Share Posted March 29, 2014 AMENDED AFTER CROSSED POSTS Probably. Modern cars do drain some current at rest for alarms and life support for some fancy electronics, and IIRC someone in another thread had a rule of thumb for allowable current. I'd take it to an auto electrician after simple things as suggested above. Just one other thought: it's unlikely with your story, but new batteries can be duff. Jonathan Edited by - Jonathan Kay on 29 Mar 2014 12:16:47 Link to comment Share on other sites More sharing options...
garybee Posted March 29, 2014 Share Posted March 29, 2014 250 milliamps is quite a lot and does suggest a current draw that shouldn't be there. Leave your multimeter measuring current and pull fuses out one by one. When there's a big drop you've found your culprit. Edit: just noticed the 'off scale' bit. same advice applies regardless except you would be better using an ammeter that is capable of reading the current draw that you have now. Edited by - garybee on 29 Mar 2014 12:20:05 Link to comment Share on other sites More sharing options...
Smegnoguk Posted March 29, 2014 Author Share Posted March 29, 2014 It is a crude multimeter but I have tried again and after the initial deflection it settles at 50 milliamps. Link to comment Share on other sites More sharing options...
Smegnoguk Posted March 29, 2014 Author Share Posted March 29, 2014 I have located the 50 milliamp drain to fuse 9 which is described as "Backup" in the manual. What does this do? Can I just leave it out? Link to comment Share on other sites More sharing options...
tbird Posted March 29, 2014 Share Posted March 29, 2014 50mA is negligible that would take well over a month to drain a 50Ah battery, if it was 50 mA it should not have gone off the scale on the 250mA range doesn't make sense, can you borrow a decent Multimeter ?, to drain a 50Ah battery in 3 days would be closer to 700mA but to flatten it enough not to start Maybe 500mA which would fit with what you said re going off 250mA scale, are you sure its reading 50mA not 500mA.  Tim Edited by - tbird on 29 Mar 2014 14:25:00 Link to comment Share on other sites More sharing options...
Smegnoguk Posted March 29, 2014 Author Share Posted March 29, 2014 Talking to myself here but nothing unusual there. Backup lights are REVERSING LIGHTS! 😬 Might just leave that fuse out for a bit to see if it solves the problem Presumably making sure the gear stick is nowhere near reverse when parked is also a good idea. Thanks to those who responded. Just spotted your reply Tim. It was definitely off the scale at least twice so fault may be intermittent. Will get a better meter today. Many thanks again to all. Edited by - Smegnoguk on 29 Mar 2014 14:24:44 Link to comment Share on other sites More sharing options...
tbird Posted March 29, 2014 Share Posted March 29, 2014 various Honda forums suggest the fuse marked "Backup" is for radio / head unit, and clock, there do seem to be a few similar problems around,, he hasn't just fitted a new stereo system by any chance, Tim Link to comment Share on other sites More sharing options...
Smegnoguk Posted March 29, 2014 Author Share Posted March 29, 2014 No new stereo. Seems to me that if 50ma is normal and there is an intermittent 250+ma drain I haven't yet located the correct fuse. Link to comment Share on other sites More sharing options...
tbird Posted March 29, 2014 Share Posted March 29, 2014 Intermittent drains are not only very unusual but will be a real bugger to find, so 500mA at 12v you are looking at something using around 5 or 6 watts of power exactly what a bulb would use, Boot light maybe, under bonnet light, has he got a big PA fitted, maybe not shutting down properly, powered sub don't know just chucking some ideas in the pot, but its going to be fun :-) Sorry Ian just noticed you suggested same Tim   Edited by - tbird on 29 Mar 2014 14:44:02 Link to comment Share on other sites More sharing options...
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