The Baron
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| posted on 13/4/24 at 04:17 PM |
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Alternator high output….
Hi all,
I’m in the middle of performing a rewire on my Locost.
I have the wiring at a stage where the engine will start and run quite happily, so now moving on to the other systems.
I happened to check the alternator output whilst the engine was running, before I actually connected the alternator charging cable…… it was pushing
out 28v which seems a lot……
Is this normal? (was expecting 13.8 to 14.8 ish)
Any ideas.
Cheers in advance
Baron
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obfripper
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| posted on 13/4/24 at 04:37 PM |
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Without the battery connected in the system, the regulator will not be able to control the output voltage.
There shouldn't be a fault once the battery is wired in, it's also the reason you should not run an engine without a battery (or disconnect
the terminals while running), as the voltage getting to those levels can mess up a lot of ecu's.
Dave
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The Baron
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| posted on 13/4/24 at 04:51 PM |
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Cheers,
I’ll connect the wires up tomorrow, and give it a try,
Thanks
Baron
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gremlin1234
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| posted on 13/4/24 at 05:23 PM |
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quote:
Originally posted by obfripper
Without the battery connected in the system, the regulator will not be able to control the output voltage.
There shouldn't be a fault once the battery is wired in, it's also the reason you should not run an engine without a battery (or disconnect
the terminals while running), as the voltage getting to those levels can mess up a lot of ecu's.
Dave
a friend of mine, long, long ago, had a motorbike that was doing very strange electrical things, it improved when we turned the headlight
on, to give it some load.
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The Baron
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| posted on 14/4/24 at 09:04 AM |
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Quick question,
With regards the small positive cable from the alternator, is it best to connect this to permanent positive, or switched / ignition positive?
Cheers
Baron
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obfripper
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| posted on 14/4/24 at 06:18 PM |
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Depending on the alternator you have fitted.
The main thick cable from +b directly to the battery, or to the main starter wire if it is more convenient (commonly used on many modern engines).
If it has a single auxillary wire (usually marked +d), then it should go through the indicator bulb (or load resistor/led combination) to the switched
live.
If it has 2 or 3 wires, then it will have one wired as above, and then either/other directly to switched live (marked ig), and/or one directly to the
battery (marked s).
Any other marked terminals can be ignored as they are usually test points used when the alternator is built.
Dave
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The Baron
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| posted on 18/4/24 at 05:23 PM |
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Ok… I’ve connected the alternator in.
I connected the thin brown wire to the switched live.
With the engine running, I’m getting 14.8 volts across the battery terminals, which I think is correct?
With the engine off, and the battery cables disconnected from the battery, I checked the continuity across the leads, and was surprised to see there
was still continuity. So set the meter to resistance and got 1400ohms…. Is this normal?
Thanks in advance, I’m a little out of my comfort zone,
Cheers
Baron
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obfripper
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| posted on 18/4/24 at 07:21 PM |
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That is the correct regulated voltage for a modern lead-calcium battery, alternators designed for the older lead-antimony battery technology used a
14.4v voltage regulator as a slightly lower voltage is required to achieve a full charge.
Which lead are you measuring back to earth? If it is the main battery cable, a resistance of 1400ohm would indicate a quiescent current of around 9mA,
which is a reasonably low amount, as it will be a normal combination of the regulator being in circuit and possibly slight current leakage of the
rectification diodes.
If it is the thin cable, it is connected to a switched live and so will not affect the battery without the engine running. It will draw current in use
to feed the slip rings on the alternator armature, this current is what controls the output voltage of the alternator and is a normal function of the
regulator.
For a 40Ah battery, this would give roughly 100 days+ standby and a battery will self discharge by nearly half in that time without being connected
anyway.
It's not enough to be worried about, and you may also find the way the meter operates may make the resistance appear lower than it actually is,
an accurate amp clamp or in circuit dmm ammeter would confirm the actual quiescent current but would not be necessary.
On a modern car, I would be looking for the total quiescent current with everything shutdown to be in the 20-40mA range,and issues are not normally
noticeable until it is above 60-100mA depending on the battery size.
Which terminal type(s) did your alternator have?
Dave
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