car battery charger

If the car has a good sun outlook buy a solar charger.

EdGasket wrote: »

It's not just relays though; unsmoothed rectified AC will take out electronics as will switch-mode supplies if not properly smoothed. All in all its safest to disconnect the battery but I accept that can be inconvenient and cause issues with programmed accessories.

A car is one of the most hostile environments for electrical and electronic devices, there is constant electrical noise and transient voltage spikes from the ignition system and the charging system.

The biggest issue with charging on vehicle, is that if the charger voltage exceeds the alternator output voltage (usually 14.4v), the alternator tries to regulate that voltage down and in doing so may fry itself. Also and i'm speculating, the alternator isn't moving, therefore it's cooling fan is not doing anything.


A smart charger regulates the voltage and current, a switching charger (like relay controlled one from Aldi), outputs a constant high voltage, doesn't regulate, it just cuts off the output when the battery voltage reaches a certain level, this perfectly fine until it switches back on, at which point there will be a spike of it's maximum voltage (which could be anything up to 18 volts).

Best way to describe it, is like a tap, if you fully open that tap instantly, you get a burst of water and then it quickly slows to it's normal flow rate.

ian103 wrote: »

Thats what I thought, it gets used 2-3 times a week for 10-20 miles etc time, I just dont think that gives it a sufficient boost given the amount of things that draw current.

That's exactly the situation I had a few years ago with a daily commute of only 10 miles with more significant mileage only at the weekends.

In the Winter what with wipers, radio, heater fan, heated screens front and rear, heated seats plus heated steering wheel on, the battery was struggling to start the engine come Thursday morning.

That's why I bought the Lidl charger to leave on the car overnight on the Wednesday thereby having a full battery for Thursday morning run.

Strider590 wrote: »

The additional electrical load doesn't help, but the real winter battery killer is simply the cold. The alternator can easily handle all the electrical systems and still put the usual charging current into the battery.

Very true. We've had a few noticeably colder days here, and my MX-5 (tiny battery) is really feeling it. When I leave for work (6 pm, approx. 10 degrees) it turns the engine over fine, but when I come home (6.30 am, approx. 3 degrees) it struggles a bit. And that's with a battery less than 2 years old.


There is also the point that with a low usage pattern the driving may not be putting back the current used by the starter, so even without lots of electrical loads the battery charge may be on a downward trend. I used to know a guy who kept his old car in the garage over winter and started it up once a week 'to make sure everything was OK'. He ran it no more than 30 seconds each time (bad idea for all sorts of other reasons) and was surprised that come Spring his battery was dead. "But I started it every week!" Yes, that's why.