Subaru alternator set up question

[Sir Fergie]

Good evening guys and gals

Giving consideration to purchasing a new to me car at some point soon (hopefully)

Looking at different options and have already been on the Ford section with a query.

Like the look of the Forester - the original type and the 03 to 04 era type.

Just a question for you guys on the alternator/battery set up on the Subarus, i seem to recall reading (in Auto Express or somewhere) that foresters have a set up where the alternator doesn't start charging the battery until the engines warmed up.

Is this correct - and if it is - two questions - when did Subaru bring it in or is this something theyve always done. And is it possible to safely modify the set up so that it starts charging the battery right from engine start up (im not talking about a botch job - i mean somethng like - a simple by pass of the switch so theres a supply of power from alternator to battery.

I realise that it may not be possible to do this safely - which is fair enough - would leave well alone in that case. Ive seen a car go on fire (not mine thankfully) and its not an experieence i want to see again.

Incidentally - do Legacys have the same set up as well

Thanks guys

Sir Fergie

[cheesesliceking]

I remember reading this about the Impreza bugeye too, so maybe its all the Subaru range from around that period? I think its Parkers that stated it.

Anyway, I've had a bugeye for 12 months and never had a problem with the battery not charging, so not sure if it would be a problem?

[peter8171]

A few years ago, I had to change the battery in my Impreza due to a faulty cell. I was told that if you want to override when the alternator comes on, use dipped beam and this forces the alternator to start charging. Having said that, I do short runs fairly often and haven't had an issue with this battery for about 4 years now.

[ScoobieWRX]

There are tables in the ECU mapping on all subaru that regulate idle rpms when you're either using air-conditioning, at high electrical load, coasting out of gear, or cold startup.

From about 800-850rpms the alternator starts charging.

[Sir Fergie]

Thanks guys

ScoobieWRX - im assuming reading your answer that the alternator will work above 850 rpm - without the need for the car to warm up. Is that correct.

Thanks a million

Sir Fergie

[ScoobieWRX]

Yes.

Best way to check it is to get a multimeter across both terminals when you start it from cold and see what voltage is going in.

You'll find cold start rpm's could be as high as 900-1000 in which case it will definitely be charging at somewhere over 14v and as the rpms come down you can see the charge rate come down too till it settles at around 13-13.5v when it's warm and idles at the usual 750rpm. It still trickle charges when it's on idle so there isn't ever a time when it's not charging.

There is nothing in any of the ECU maps that as far as i can tell from looking at the tables on any ROM that have anything to do with regulating the alternator due to engine coolant temperature although there may well be unidentified hidden tables (as there are still many) that play some part in that job.

Right now and without physically checking i can say it charges from cold but please check for yourself.