Charge or jump start?
Discussion
I've been recovering from an operation for the last 6 weeks and my weekend MK 3 MX5 has been in the garage for all of that time as a result. And the battery is flat. The remote control unlocks the car and all the warning lights come on when I tried the ignition...just wondering whether it's totally dead and needs jump starting or whether I can buy a charger and that will sort it out?
shake n bake said:
A battery charger will give it a thorough charge, if you do jump it, leaving it to just idle does close to nothing. Driving it's ok though.
True - at the moment I probably can't drive it far so maybe a trip to Halfords for a charger is the best option at the moment. Ta for the reminder.Galveston said:
shake n bake said:
if you do jump it, leaving it to just idle does close to nothing.
It should charge very well at idle.
Old cars with dynamos were hopeless at idle but a modern alternator should be capable of simply increasing the load on the engine to get the desired output regardless of engine speed. However, a good variable-voltage battery conditioner (as opposed to a simple charger which isn't the same thing at all) is capable of recovering a battery which a fixed-voltage alternator cannot. It's a useful thing to have anyway.
Buy a Ctek from fleabay if you can. They're currently (sic) the best out there for a charge or to leave attached for a maintenance charge. They also have recovery capabilities to desulphate heavily discharged batteries. If you're in no rush, give it a good charge. As a caution note, some modern vehicles do not respond favourably to jump starts. While the chance is very slim, there have been some electronic component failures due to jump starting. The VW T5 and the new Ford Ranger are two.
Another vote for a ctek. I have the MXS5.0 charger and it's bloody great. Also been recovering from an op which meant my licence has been revoked for 12 months, I've had friends drive it periodically but the charger has stayed on pretty much every time the car isn't in use and the car has started faultlessly every time.
Thanks for that - just reading about the CTEKs now. My old Camaro never seemed to mind being stuck away for a few weeks - the worst that would happen is the electronic trip counter would reset to zero but it would always start first time. The MX5 I guess has a far smaller battery. Lesson learned! Looks like a CTEK is a good idea.
I've got a CTEK and am very happy with it. It's recovered at least two batteries that I would have thrown away before I had it so in that respect it's paid for itself. Regularly conditioning my Elise's battery (the Elise alarm is renowned for killing the battery) has taken it from lasting 3 days before it goes flat to being perfectly happy after two weeks. 
If you've depleted the battery enough to require a jump start then at the earliest opportunity you should remove the battery and charge it for around 20 hours to ensure that it is fully replenished.
Lead acid batteries charge best at a rate of C/10 where C is the capacity in Ampere hours; for a 105 Ah battery this would be 10.5 Amps.
http://batteryuniversity.com/learn/article/chargin...
"During the constant-current charge, the battery charges to about 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours. The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If continually deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge."
Lead acid batteries charge best at a rate of C/10 where C is the capacity in Ampere hours; for a 105 Ah battery this would be 10.5 Amps.
http://batteryuniversity.com/learn/article/chargin...
"During the constant-current charge, the battery charges to about 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours. The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If continually deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge."
Flip Martian said:
My old Camaro never seemed to mind being stuck away for a few weeks - the worst that would happen is the electronic trip counter would reset to zero but it would always start first time. The MX5 I guess has a far smaller battery.
Or more always-on electronics giving a bigger drain.Galveston said:
It should charge very well at idle.
Well my experience says all the cars that go flat on the forecourt and are left to idle for hours to try and charge then generally last a few days at best. If charged properly then they are fine for weeks after. Anything Japanese, Korean or fords are the worst culprits.
Something to do with only producing enough power on idle to keep it running apparently.
If that's the case, they have a really crappy charging implementation. Surely the whole point of having an alternator over a dynamo is that engine speed has no bearing on electrical output?
I wonder if not charging the battery at idle is another one of these adft things they do to fool the emissions tests? NEDC spends quite a lot of time idling and I bet they don't check that the battery is in the same state of charge at the start and end of the test.
I wonder if not charging the battery at idle is another one of these adft things they do to fool the emissions tests? NEDC spends quite a lot of time idling and I bet they don't check that the battery is in the same state of charge at the start and end of the test.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff