Car Battery

Joe_Horner

Strider590 wrote: »

Not measuring Amps, just voltage.
You don't actually need to disconnect the charger, the voltage before the diode (which is usually separate to those solar chargers and is there to prevent the battery discharging into the panel) MUST be at least 0.7 volts higher than the battery voltage before any current can flow into the battery..... If not 0.7volts higher then effectively it's the same as having the charger disconnected.

Tis how diode's work

The problem is that, because a forward biased diode will always show (about) 0.7v once it starts to conduct, it will pull the battery voltage up to 0.7v below the panel output virtually as soon as you connect. So you can never be sure that way whether it's actually charging or just about to turn the diode on but not putting anything in.

If you measure the battery voltage disconnected and then again connected then an increase is a definite indication of charging, although an ammeter check is better cos it shows how well it's charging rather than just yes / no.

Incidentally, anyone who forgets to switch a multimeter from amps to volts before checking a mains socket won't forget the next time (although I stuck 100Ω resistors into the end of tape player mains leads cos it made a good bang a few times as a kid )

eprophet

Hi,
I just wanted to say thank you to everyone for all the advice. To be honest the technical stuff, although very interesting, is over my head.

I emailed Bosch and the RAC (they fitted the battery) as well.
Bosch sent me a kind and thoughtful reply and said that it should still be ok if left for 3 weeks. The RAC have not yet replied.

Thank you everyone I'll let you know how I get on.

gord115

Have you thought about an intelligent battery charger that can be left connected long term?
Then the battery will always be fully charged
.http://www.amazon.co.uk/CTEK-Multi-Functional-4-Stage-Battery-Charger/dp/tech-data/B004TLF4PC/ref=de_a_smtd