Car battery charging current.

[Roger Hayter]

on a battery charger, the starting currents through the charger would be around 4 amps in the worst case, coming down slowly to 0.5 amps in about

12/16 hours; if this is any guidance the alternator charging load would

Unfortunately, it isn't any guidance at all. Battery chargers are limited in current by price, and thus the size of critical components. They take a day to significantly charge a flat battery, while the alternator has to recharge, say, a quarter of the capacity in a matter of tens of minutes. I looked up maximum charge rate for lead acid wet batteries and apparently 0.3C (a very few tens of amps for a car battery) is recommended routinely but up to 1.5C (over 50A) can be used for short periods with a partially discharged battery. (C of course is a current in amps equal to the amp hour capacity of the battery to a first approximation.)

[GB]

It's all in your tin foil head .

[Dave Plowman (News)]

6 to 10 hours driving is far more than many cars ever get.

Given most cars these days have plenty alternator capacity, there really shouldn't be the need to ever charge the battery externally. Unless the car is not used for such a time as the battery goes flat.

[Dave Plowman (News)]

Yuasa is the posh brand Halfords sell for car batteries. Used to be Bosch.

[The Natural Philosopher]

1.5C in a 75AH battery is around 110A.

I used to charge nickel chemistry batteries at 3C! LiPo at 1C, but even those are now able to be charged harder

Anyway the point is that even at idle a big alternator is capable of tens of amps. Not the <5A originally claimed.

Manufacturers have a trade off between having batteries fail through being flattened in multiple cold starts or failing through overcharging.

But they are not limited by alternator technology.

[Dave Plowman (News)]

The internal impedance of a battery is a bit of a red herring. Given they can deliver perhaps 600 amps at starting.

[Dave Plowman (News)]

Both Lidl and Aldi do a rather nice SMPS one for about £14. Aldi may have it available online at all times - Lidl as a special offer a few times a year. Similar in spec to a Ctek at 4 times the price. Much smaller than a traditional charger, and better too.

[Dave Plowman (News)]

If it were to measure everything in a modern car, it would need to be 100

0 100 or more.

But a pure analogue ammeter is very expensive to fit, due to the very heavy cable needed to the dash. Hence them not being fitted these days.

You can measure the voltage drop in a battery lead - either plus or minus

- and calculate the charge/discharge current to the battery. But doing this to sufficient accuracy to be of use, likely not cheap.

[Dave Plowman (News)]

That is a crude charger. And a pretty small one if it peaks at 4 amps.

[Dave Plowman (News)]

Brilliant devices. Work near instantly. Unlike the car heater.

[Roger Hayter]

Exactly. The situation changed dramatically when alternators replaced dynamos. After this the limitation was rather crude electo-mechanical controls. Before that, everyone had a battery charger!

[charles]

It's now 7 weeks since I used my car.

[gopalansampath]

I guess everyone is talking Of the order 80 Amps and higher without thinking. A casual observation of cables that carry the currents are not thick to carry such high currents and such high current handling is a safety hazard. Also, given the fact that cars move and hence the vibration will cause heavy sparking and damage the wiring. Only the cable from battery to the starter motor is thick as it carries a peak current of upto 400 amps At engine cranking moment but then to a fraction of a second and not continuously!

[Roger Hayter]

The idea that disturbing a fitted cable can cause huge electric discharges and fires is a Hollywood meme with no basis in reality.

[Fredxx]

That's not my experience for a Chinese sourced Bosch replica on a boat application, where the alternator will happily kick out 150A over a prolonger period.

One of the reasons why high amperage alternators is specced is all the electrical power needed when all the car appliances are used, rather than just topping up the battery between starts.

[Fredxx]

Most battery manufacturers suggest a charging current at C should be considered a maximum, so an arbitrary 50A doesn't cover many battery specs.

YMMV

[mm0fmf]

The alternator on my car is 180A.

2x heated seats 1x heated steering wheel 2x heated mirrors 1x heated rear window 1x cabin heater booster 1x electric water pump 1x electric power steering

Plus dashboard/infotainment electronics and God knows how many ECUs/processors elsewhere. 100% LED lighting.

The current for charging the battery is a small part of the current drawn by the car. Full ECU controlled alternator with dynamic load shedding and regenerative breaking.

Driving to work and back twice a day kept the battery well topped up and the start/stop became active quickly as the engine/trans warmed and the battery was charged enough. Driving short distances twice a week at most, the start/stop never becomes ready. Not seen stop/start become ready since I started working from home, a week before lockdown.

[mm0fmf]

How dare you question the turnip.... he's got a special degree.

[williamwright]

Yes, intelligent chargers with a temperature sensor strapped to the side of the battery.

Bill

[Dave Plowman (News)]

The peak output of a dynamo on the average car fitted with one was under

30 amps - 24 being a common size. Plenty 50s cars didn't have enough output to drive all the electrical bits then - let alone what we are used to now.

Rolls did fit an adequate size dynamo with electro mechanical regulator.

An alternator is much cheaper to make than an equivalent dynamo. But had to wait for cheap enough rectifiers to be practical. So saying, electronic control can improves the performance of a dynamo too - if not the peak output.