Low alternator output at startup

[10G]

I've noticed the last few days that the scanguage is telling me at first start up in the morning, that my voltage reading is at high 11's low 12's eg: 11.9v. This is while it's still idling in the shed.

Once driving it goes up to high 13's.

Is that normal??

Should the alternator be throwing out high 13's low 14's from the very first second?

Could it indicate that the alt is on the way out??

Thanks for any help.

[mudnut]

Give it above 1500 rpm just after start up and see if it immediately raises the voltage. It should be around 14.2 volts after that.

[10G]

Thanks Craig, I'll give it a go this evening.

[the evil twin]

More likely battery than Alt if indeed anything is wrong at all.
Esp for a Diesel with high current load on startup from the Glow Plugs etc.

As Mudnut said give it a few revs to check Alt and maybe give the Battery a tickle up with a smart charger in Recond mode to get rid of any Battery sulphation.

[10G]

Thanks ET.

Checked it again this morning. Immediately after start, first think in the morning, the scanguage said 12.1v, checked that with a multimeter on the battery, same reading.

Gave it a rev for maybe 1.5 secs, it came up to 13v and sat on 13.9 as I drove.

I will charge up the batteries and see what happens.

I was also wondering if I'm asking too much of the alternator??? I have 3 batteries. Normal crank (105Ah), a 2nd (105Ah) which is charged via a Redarc SBI12 and a 3rd (210Ah lifepo4) which is charged via a 40A DC-DC charger.

I was wondering, if the alternator is being asked to do alot of work, would it get hot/very warm??? After a 45 min drive, it was just warm. I don't know if that indicates that it's not being asked to do alot or not???

[mudnut]

Drive the vehicle for a while, to top off the battery after startup. Check the output with the headlights, radio and wipers on. If the volts drop significantly, even with over 1500rpm, then maybe get the alternator checked out.

13.9 V is on the lower end of OK, and should rise after a few ks of driving.

[10G]

Thanks Craig, I'll do that this arvo.

Been looking at alternator specs. Apparently the alternator in the Y61 (ZD30 / CRD) is a 90 amp unit. It only puts out 55-60 amps at 2200 - 2500 rpm (which is my rev range at 100km/h), you get close to 90 at 4000rpm.

The TB45 alternator puts out 80 amps at 2500 rpm. This has me wondering if a TB45 alt can be modded to fit the ZD30??????

[mudnut]

The oil burner gurus will have to help you with that.

[the evil twin]

Thanks ET.

Checked it again this morning. Immediately after start, first think in the morning, the scanguage said 12.1v, checked that with a multimeter on the battery, same reading.

Gave it a rev for maybe 1.5 secs, it came up to 13v and sat on 13.9 as I drove.

I will charge up the batteries and see what happens.

I was also wondering if I'm asking too much of the alternator??? I have 3 batteries. Normal crank (105Ah), a 2nd (105Ah) which is charged via a Redarc SBI12 and a 3rd (210Ah lifepo4) which is charged via a 40A DC-DC charger.

I was wondering, if the alternator is being asked to do alot of work, would it get hot/very warm??? After a 45 min drive, it was just warm. I don't know if that indicates that it's not being asked to do alot or not???

OK... few things to comment on in the quote.

At idle your Alt will be lucky to put out 40 maybe 45 amps so any load over that will cause the voltage sag you are seeing.

I reckon your Alt is fine, if you had dropped a diode/s on any phase then you wouldn't get 13.9 Volts at higher RPM.
On cold start at idle with glow plugs etc the load on the Alt is causing the voltage to sag to 12 ish volts due to high current draw.
The few revs generates a higher current output from the Alt so the voltage can now rise as well until the current draw is low enough for the Reg to do it's voltage limiting job at 13.8 to 14.2 nominal volts.

Cranker and Aux of the SBI12 will not be much of an issue unless the Aux is down on charge as well.
If the Aux is 80% or better then it won't pull much current.
If the SBI12 is energising within a minute or so and linking the Aux then the Cranker and Aux should be OK
If the SBI12 is energising/deenergising IE "cycling" then the Aux is drawing a lot of current so it is down>

The LiFePo current draw is limited by the DC/DC to 40 amps max BUT that is a fair wack if the battery is down even a little and the DC/DC wants its share of the load from the Alt as well as Glow Plugs, Cranker etc (etc meaning A/C fan, lights and anything else).

Bottom line is I reckon everything is probably OK and maybe do a recon with a smart charger or capacity check of the Cranker.
FWIW I used to try and have the same batteries (I like Caterpillar Batts) as Cranking and Aux and swap them across every 12 months or so and used to get 4 or more years life out of them easy peasy.

[10G]

OK... few things to comment on in the quote.

At idle your Alt will be lucky to put out 40 maybe 45 amps so any load over that will cause the voltage sag you are seeing.

I reckon your Alt is fine, if you had dropped a diode/s on any phase then you wouldn't get 13.9 Volts at higher RPM.
On cold start at idle with glow plugs etc the load on the Alt is causing the voltage to sag to 12 ish volts due to high current draw.
The few revs generates a higher current output from the Alt so the voltage can now rise as well until the current draw is low enough for the Reg to do it's voltage limiting job at 13.8 to 14.2 nominal volts.

Cranker and Aux of the SBI12 will not be much of an issue unless the Aux is down on charge as well.
If the Aux is 80% or better then it won't pull much current.
If the SBI12 is energising within a minute or so and linking the Aux then the Cranker and Aux should be OK
If the SBI12 is energising/deenergising IE "cycling" then the Aux is drawing a lot of current so it is down>

The LiFePo current draw is limited by the DC/DC to 40 amps max BUT that is a fair wack if the battery is down even a little and the DC/DC wants its share of the load from the Alt as well as Glow Plugs, Cranker etc (etc meaning A/C fan, lights and anything else).

Bottom line is I reckon everything is probably OK and maybe do a recon with a smart charger or capacity check of the Cranker.
FWIW I used to try and have the same batteries (I like Caterpillar Batts) as Cranking and Aux and swap them across every 12 months or so and used to get 4 or more years life out of them easy peasy.

Thanks ET, I tend to agree.

Everything seems to be working like it says in 'the book'. Last night I sat her in the driveway, turned on the AC, fan, lights on high, wipers, rear light and the reading on the cranker was high 13s. The AC kicked in and it dropped to 13.2.

I did a full recondition charge on the cranker last night. I'll do one on the aux battery tonight.

How long do the glow plugs stay on for??? I just thought they got turned off once the light went out on the dash.

Thanks for the help.