Lead acid battery charger (or alternator) switching to trickle with (2025 Update)

Scotland.

I've seen Ford, Fiat, VW, Renault, Rover, Range Rover. Always 2 or 3 cables. Far easier to attach them all to the battery. That way you have a wire straight from the battery to the starter, no junction boxes to give resistance.

Probably because you're replacing just one of them.

As above, resistance. And of course you don't need a junction box which needs to be mounted somewhere and thoroughly insulated from the chassis. In my current car, the battery is mounted right next to the fusebox. A wire goes from the battery to that, to supply power to lights, etc, etc. The starter is about 2 feet from the battery, diagonally below it and under the engine - another wire goes to that. The alternator is on the other side of the engine, a third wire goes to that. It would be pointless to join these anywhere other than the battery terminal itself - why would you want to do that? To save a tiny bit of wire at the expense of having a junction box providing resistance and taking up space?!

It makes your post pointless as you're not conveying your meaning.

Yip - same reason in your house you connect the wire to power your sockets from the fusebox to one socket, then another, then another, you don't have seperate wires going from the fusebox to each socket. That would be utterly pointless. In the car you might aswell use the battery terminal as the junction box. That way everything has the full battery voltage only one cable away.

And my claim that my car's alternator drops from 144V to 13.8V when the battery becomes full.

You do realise wires have resistance?

I can tell you how an alternator does it, chargerscan do it differently. AN alternator doesn't "switch to trickle charge". AN alternator limits the output voltage. A battery will only accept a certain amount of charge at any voltage. At 14.6 volts it basically stops taking a charge. The regulator is set to limit the voltage to a specified voltage - 13.8 or 14.2, or something similar. An alternator is intrinsically current limitted so will not provide more than the rated current, If the battery open circuit voltage is below 12 volts it will tale pretty close to whatever the alternator can put out, as the open circuit voltage increases, the amount of charge it will accept decreases, untill at 14.6 volts or whatever is designed as full charge, it will no longer accept ANY charge. As the load changes, the alternator provides more or less current as required to maintain the fully charged voltage.

Clear as mud???

A generator generally used a "3 unit regulator" Onewas the cut-out - which is replaced by the diodes in an alternator. The alternator cannot drain the battery attempting to "motor" itself like a generator. The second unit was the current regulator, because a generator is NOT self limitting. If you full feild a generator into a dead short it will melt itesrlf down.

An alternator is self limiting due to it's higher stator resistance.It will ONLY put out a certain amount of current into a load, regardless of the resistance of the load. This is due to both the stator resistance and the maximum flux of the rotor - so the current regulator (actually "limitter" as it only controls the maximum output) is not required on an alternator either. This leaves the voltage regulator, which controls the feild current either linearly or by "chopping" - or pulse width modulation. The more current flowing in the feild the higher power produced - in volt-amps. As the current changes, the voltage changes in reverse, for the same feild strength. Higher current = lower voltage. By sensing and controlling the voltage the current pretty much looks after itself - as the regulator controlls the feild strenth by varying the feild current. It controls the feild current by controlling the voltage impressed across the feild coil.. As the engine speeds up, it requires less feild strength to produce the same voltage.

SOME chargers - and some vehicles that use the computer to control charge, use a "3 step" algorythm which uses constant current to "bulk charge" the battery to a certain level, then switch to constant voltage untill output current drops below a certain point where it switches to "float charge". Not COMMON on cars, but getting pretty common on higher end chargers to prevent overcharging and gassing of the battery when left on charge. The old service station type chargers had a simple timer to accomplish this - and some of the later ones had a combination - when charging voltage exceded a certain point it would charge for anothe X number of minutes before shutting down.

Automotive charging systems that actually sense current are EXCEDEINGLY RARE.

It senses voltage so it can keep it steady. Voltage does not change when the battery gets full, the current draw changes.

How can the battery change the voltage when it's kept steady by the regulator? Find a graph of a battery being charged. Once it draws less than the maximum current the charger can provide, it stays at precisely the same voltage for the rest of the charge, and the current gradually drops. The charger senses this current drop and changes the voltage to different levels to enter the three charging phases.

Well sane people only moan about something daft he says once, when he says it. Collecting the quotes and repeating them over and over just makes you more of a troll than him.

Show us any reference that says this is what is actually done. Waiting...... Nuff said.

The Zener will limit the voltage to something like 14.2V or thereabouts, with temperature compensation. The ideal rate for charging a battery lies in the range 13.8-14.1V. This range provides the maximum battery service life and limits the heat generated within the battery. The disadvantage is that the charge time is much longer and there exists a risk of sulphation. Between 14.4 and 14.7V there is less risk of sulphation but a higher risk of grid corrosion on the positive plates and gassing. This will require topping up of the water content of the electrolyte and can cause severe overcharging if ambient temperatures are high.

And that voltage increase is in step with battery internal resistance.

It will only be muddy to those without a clue. ;-)

I wouldn't have thought it a particularly difficult set of concepts to understand, especially in this day and age when there are heaps of texts on the topic describing the operation of *all aspects* of a vehicle's electrical system and freely available on the internet. All that is required is an understanding of the fundamentals of electricity and, these days, electronics.

A car charging system is unlikely to ever really *need* a float charge mode since it has to deal with other electrical system loads as well as the needs of the battery. That and the type of use the car battery gets adds a layer of complexity to it all that I can't see is really warranted. A battery charger, on the other hand, has to deal only with one load, the battery.

I've never seen one.

His car clearly doesn’t, f****it child.

Don’t need one, he car clearly doesn’t keep the voltage constant, f****it child.

It looks at the *voltage*. It operates on the *voltage* and it alters the voltage according to the needs of the battery and the rest of the electrical system.

The voltage is referencing the battery internal resistance. That resistance changes (rises) as the battery charges.

The open circuit voltage of a battery is indicative of its state of charge;

Voltage | 11.7 | 12 | 12.2 | 12.4 | 12.6 or more % Charge | 0% | 25% | 50% | 75% | 100%

No need to look at *current* to work out charge rate, the voltage reading does the same thing.

Bullshit it is when the battery is being charged by the alternator in a car.

Bullshit it does when the battery is being charged by the alternator in a car.

There is no open circuit voltage then its being charged by the alternator in the car.

Pity that there is no open circuit voltage then its being charged by the alternator in the car.

Just because YOU added no loads doesn't mean the loads in the car are not changing.

I think it actually dropped gradually if that means anything. I actually did that test because someone in one of these groups (although some troll has deleted half the groups, so I've added them back in AGAIN) told me that a car alternator changes voltage, this was in a post 6 months ago.

Given that it's typically a dumb, passive component device, that seems unlikely. And if it's true, then there should be plenty of discussion about it at online resources, yet so far, neither you nor Rod can produce anything.

How about you stop speculating and show us some references?

Yeah, the UK is a real powerhouse in the auto industry, what with Triumps that fell apart and all.

We had a mechanic confirming it when I was saying it since I am also a mechanic. Served an apprenticeship and been in the trade since the 60s. ;-)

Oh, didn't know that. There may be a different, more advanced charging system on some new cars, but no one has been able to show it or why it would be used. And meanwhile making claims about it, how it works, is just the usual BS. And we know the basic alternator/VR system that just targets a voltage has worked for the better part of the last century.