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Location:
Canberra
Registered:
February 2004
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Voltage question, with ignition on.
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Fri, 04 November 2005 03:29
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Bit of a weird one here, the problem I have is that when my engine has been running for a while the voltage at the battery is going down to 13.6 volts and below. I've upgraded the battery to alternator cable and the alternator gives the same voltage at the pole. I've noticed one strange thing though, with the ignition on I'm getting a bit of a power drain, the battery voltage is dropping to 12.0 volts without the engine running. The question is what sort of amp draw should I get with the ignition on? I'm thinking maybe the diodes have shorted in the alternator.
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Location:
SE. Melbourne
Registered:
August 2002
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Location:
Brisbane
Registered:
July 2005
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Re: Voltage question, with ignition on.
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Fri, 04 November 2005 05:47
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Yeah doesnt sound like there is anything too abnormal if this is at idle.
Like was said, get some revs happenin and tell us if the voltage goes up with revving which it should.
What kind of battery do you have too...
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Location:
Bottom of the hill, Sydney
Registered:
April 2004
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Re: Voltage question, with ignition on.
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Fri, 04 November 2005 09:46
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To really know if the alternator is working correctly you need to check how much current it is putting out.
With the engine running all the vehicles electrical system should be running off the alternator. There should also be current going into the battery. The alternator will put out alot of current when the battery is flat and taper the current off as the battery charges. The voltage should be somewhere around 13.6v to a max of 14.4v but some newer cars can have a max charging voltage of around 15v.
If you can get your hands on an amp meter check the charging current with all the electrical systems turned on (ie head lights on high beam, fan on full speed, rear window demister on, etc).
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Location:
Townsville North Qld
Registered:
June 2003
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 Re: Voltage question, with ignition on.
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Fri, 04 November 2005 10:09
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sounds normal to me. With the amp meter, i would not suggest doing that unless you are familiar with the use of high current ammeters and have good connections. The current put out from an alternator is enough to cause a major engine bay fire, and can really sting if you get in the way of it. This should be left to the very experienced home mechanic, or professional auto lecky. Personally, even after 6 years of home mechanics, working as a mechanic at auto dismantlers and also doing performance upgrades and major vehicle modifications... i wouldnt do this myself because of the risk of injury and fire, and the cost of the ammeter required for the job (need 5 amps more than what the ammeter is capable of putting out... so 40amp for the average 18RC)
If in doubt, see a professional with that one.
Cheers, Owen
-1 month from being an electrical/electronic engineer (BEelec)... YAY!!!
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Location:
Canberra
Registered:
February 2004
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Re: Voltage question, with ignition on.
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Fri, 04 November 2005 17:06
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Bit more to this story guys, i'm using a Ford Fairlane 60 amp bosch that I got in the wreckers, that looked about right. Didnt take too much effort to put in and gets rid of that old external regulator. It went pretty good for a while but when you buy second hand it might last a day or a year. Even at 5000 revs the voltage might drop as low as 13.0 measured on a muiltimeter not on the dash out of wack scale. The car is a ra40 with a 18r-c fitted. I'll measure the amp draw at idle and see if theres a draw in the ignition circuit. Its gives about 13.9 at idle untiln it warms up and then it drops to 13.6 or even 13 flat. Its not too easy to get out because I had to change a lot to make it fit in the first place. I think when it heats the diodes mess up and drop one or two of the fields. ( I think that theres three in a bosch alternator). Anybody got any ideas?
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Location:
Canberra
Registered:
February 2004
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Re: Voltage question, with ignition on.
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Sun, 06 November 2005 13:57
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Well, one set of brushes later and we are looking good. I'm going to get the alternator load tested anyway in case its not reaching its full potential. Maybe stick in a new diode set if its not. Bosch alternators are everywhere so the parts are pretty cheap. Next time I'm down the scrap yard I'll get something like the commy 135 amp and see if I can fit the guts into my creation.
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Location:
Brisbane
Registered:
July 2005
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Re: Voltage question, with ignition on.
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Sun, 06 November 2005 22:40
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Think that they have different size stator packs. Unless you wana go as far as rewinding it...
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Location:
Townsville North Qld
Registered:
June 2003
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Re: Voltage question, with ignition on.
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Sun, 06 November 2005 23:15
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Why would you need 135 amps?? Thats just extra weight to spin. your not running an efi fuel pump... so you only need a 40Amp unit, even if you have a big coil. Ive run quite happily an 18R-C powered RA40 off the stock 35A alternator with 180WRMS competition amp, 2*10" alpine subs, pair of 6 1/2" splits and a CD head deck without ever having voltage problems even when lights and everything was on. So unless your going EFI, you shouldnt need more than a 60A alternator. Any more, and you dont get any extra advantage from it, and it slows your acceleration further.
Cheers, Owen
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I supported Toymods
Location:
Frankston, Victoria
Registered:
April 2004
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Re: Voltage question, with ignition on.
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Sun, 06 November 2005 23:49
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I only just hooked up my 4AGE alternator recently (Had been taking battery out to recharge it once a week, engine still isnt running properly and I was starting it alot to fix timing issues etc.). But yeah with the Alternator plugged in, at lock it shows 12.6V, at ignition on position it shows 12V, with starter motor running it shows around 10-11V, engine idling it shows 13.6V, and with some extra revs it goes up to around 14V.
Kev.
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Location:
Canberra
Registered:
February 2004
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Re: Voltage question, with ignition on.
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Mon, 07 November 2005 02:41
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The reason that I put it in was that my old alternator was getting noisy at the bearings and this was a heap cheaper then getting a new one. I want to run pretty strong lights up front as well so the extra power wont be going to waste. I found that upgrading the main battery wire from the alternator was pretty effective. I've found most Bosch's to sit at around 13.8-14. For some alternators back in Europe you can buy an adjustable transistor regulator that allows you to change the cut off point for the transistor. Giving you a closer to Toyota voltage of 14.2 - 14.4.
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Location:
Canberra
Registered:
February 2004
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Re: Voltage question, with ignition on.
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Tue, 08 November 2005 15:51
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As a matter of interest, if your looking for an easy 18r based upgrade in alternator then theres a 55 amp one form a hilux, I think that bolts straight in. Externally regulated, just hook it up. You'll need a longer alternator bracket though, easily made. Just the thing for all you guys who love big stereo systems.
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Location:
Canberra
Registered:
February 2004
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Re: Voltage question, with ignition on.
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Thu, 08 December 2005 16:58
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I've actually found a way to changing the charging voltage of a Bosch alternator. Apparently its affects by heat charging higher when cold and lower when hot. You can jack up the voltage by putting a resistor or diode on the regulator earth. If you remove the Bosch regulator you'll see what I mean. Don't blame me if you over cook it with too much resistance though.
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Location:
Brisbane
Registered:
July 2005
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Re: Voltage question, with ignition on.
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Fri, 09 December 2005 03:08
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You're only sacrificing charging amps for volts here arent you?
Why? Whats the benefit.
Copper wire has resistance. Its bugger all, but it goes up quite a bit with heat. More so than other conductors like silver.
There is a lot of metres of copper wire in an alternator, i think most of em charge better when they're cold...
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Location:
Canberra
Registered:
February 2004
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Re: Voltage question, with ignition on.
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Sun, 11 December 2005 18:09
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This is different mate, if you put more resistance on the regs earth you can make it switch at a higher voltage. It wont change its amp output. Bosch set their transistor switch point a bit low. I'd like to state that this is my opinion and if you want to hear from somebody that has a qualification then search elsewhere.
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Location:
melb
Registered:
May 2002
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Re: Voltage question, with ignition on.
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Mon, 12 December 2005 00:51
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I dont see what the problem is...
is your battery going flat?
if not then just get on with something else..
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