Best practice- charging

[mikewroe]

Bit puzzled, when I charge my engine battery I have always disconnected the earth to protect other devices. This is something I have always done, going back to dynamo times.
When I think about it, some new style solar charges have a feed to enable the engine battery to also be charged.
Is the current so small that it's not an issue, or have I been mis informed for years?

 

[RichardHelen262]

when we go off to Europe I connect both the wife’s car and mine to car charges whilst we are away otherwise we come back to flat batteries, and I have never disconnected the battery,

 

[wildebus]

Bit puzzled, when I charge my engine battery I have always disconnected the earth to protect other devices. This is something I have always done, going back to dynamo times.
When I think about it, some new style solar charges have a feed to enable the engine battery to also be charged.
Is the current so small that it's not an issue, or have I been mis informed for years?

Why do you think it is neccessary to to disconnect the earth when you are charging the engine battery? (I presume you mean when you connect a mains charger direct to the battery terminals).
If that was neccessary to protect other devices, what is protecting those devices when the engine battery is getting charged by the vehicle alternator?

 

[Molly 3]

Bit puzzled, when I charge my engine battery I have always disconnected the earth to protect other devices. This is something I have always done, going back to dynamo times.
When I think about it, some new style solar charges have a feed to enable the engine battery to also be charged.
Is the current so small that it's not an issue, or have I been mis informed for years?
[/QUOTE
Trev will explain later

 

[mikewroe]

Why do you think it is neccessary to to disconnect the earth when you are charging the engine battery? (I presume you mean when you connect a mains charger direct to the battery terminals).
If that was neccessary to protect other devices, what is protecting those devices when the engine battery is getting charged by the vehicle alternator?

Sorry, my phrase "devices" is misleading. I should have said Alternator, ECUs etc.
Could be that I remember something about old 4TR alternator regulators not liking a back feed?
Forgive me if I am talking out of my behind.

 

[wildebus]

Sorry, my phrase "devices" is misleading. I should have said Alternator, ECUs etc.
Could be that I remember something about old 4TR alternator regulators not liking a back feed?
Forgive me if I am talking out of my behind.

I don't know about old 4TR alternators, but you say "ECUs etc."? they are not disconnected when the engine is running and the vehicle battery is getting a charge (ie subjected to a higher voltage) from the alternator (so just the same as from a mains charger), so my point has not changed.

FWIW, I have never heard of anyone needing to do what you are suggesting and can see no reason for it.

 

[wildebus]

As an aside, on the topic of disconnecting things when charging a battery, there is a model within the Sargent EC range of PDU (Power Distribution Units) that has a charge voltage of ~15V and there is a note in the manual for that specific EC model not to connect anything to the Leisure Battery other than their PDU due to the high voltage.
The hab electrics connected to the PDU presumably go through a regulator?
I can't remember which model of EC this was and I think (I hope, anyway!) it was quite a short-lived one as a terrible idea for multiple reasons

Anyway, nothing to do with vehicle battery charging

 

[mikewroe]

Thanks for the replies. Next time I need to charge the engine battery I will just hook up under the bonnet rather than access the under floor compartment.

 

[Geek]

Is the current so small that it's not an issue, or have I been mis informed for years?

The latter, I think.
In the days of dynamos, the regulator used to switch off charging using a relay. This, combined with the high inductance of the dynamo coils, coul produce amazingly high transient voltages. Maybe 80 volts.
Of course, cars weren't full of electronics in those days.
Nevertheless, every part of modern vehicle electronics has to be able to cope with transient spikes and longer voltage surges.
A small mains charger is/was never going to pose anything like as much risk as something like turning off the heater fan.

 

[merl]

This matter has cropped up previously on WC when Barry (who else) pointed out that the Ducato manual advised against charging the starter battery while it was connected. I haven't studied the manual but AI confirms this.
I can't see an issue myself and the advice fly's in the face of everyone who has a battery maintainer that trickles the starter battery from the leisure batteries.
I think the advice probably stems partly from ancient ritual and also Fiat and most other companies covering their ass against anyone using a dumb charger or a charger with a maintenance or desulphation phase as they could possibly bring the system voltage way above the 14.4 volts maximum you'd see when alternator charging and supposedly could damage parts of the electronic system??
Pretty crappy system that won't tolerate a slight over voltage though especially when they use over voltage on modern smart alternator systems to achieve regenerative breaking.