Alternator Charging Light - Dc Charger

[garrycol]

My truck runs 24v but to provide 12v for many of its accessories a previous owner had installed a 12v 60 amp alternator. On the dash there is a 24v ignition light and a 12v ignition light - obviously these go off when alternator voltages exceeds the relevant battery power as per the majority of vehicles.

I have removed the 12v alternator and replaced it with a 24v to 12v 60 amp Dc to Dc 3 stage battery charger to charge the 12v aux battery. As was with the fitted alternator I would like the 12v ignition light to be able to light up if the DC charger fails. Now I could take power from the "on" indicator lamp on the Dc charger and through a relay to light up the dash lamp but that will only indicate that 24v power is being provided to the charger even if the charger has failed and not producing power.

What I want to do is create a circuit like is in an alternator that lights up the light on the dash when there is 12v to the alternator but it is not producing power and switches off when power is being produced. I am not sure how to do this as simply taking power for the dash light from the output side of the Dc charger will not work when it is off or failed as the battery will still provide power. The only way I can think of doing it is putting a big - say 100amp diode between the Dc charger and the battery so that battery power cannot go back to the charger but this seems a rather crude way of doing it.

Any suggestions with a bit more finesse (ideally with a circuit diagram) would be appreciated.

Thanks

Garry

[bob_m_54]

Which DC-DC charger are you using?

[VroomVroom]

might be simpler to use a voltmeter on the DCDC's output , and monitor that.

[lsemmens]

Just as a thought, did they remove the 24v alternator when they attached the 12v one or just added a 12 alternator, too? If you have two alternators, why mess with it?

[mtv]

Just as a thought, did they remove the 24v alternator when they attached the 12v one or just added a 12 alternator, too? If you have two alternators, why mess with it?

I read it as a 12V alternator was added to power/charge a separate 12V battery used for 12V accessories in a 24V truck.

This is common practice in many fire trucks.

It's a very effective method, so I too would leave it as is if that's the case.

[garrycol]

Thanks for the responses - gotta love forums as responses cover a lot of stuff often related to other issues.

Ok - charger is an OEX, yes the original engine ran both the 24v alternator and a secondary 12v alternator - truck has been re- engined and it is not practical to put the 12v alternator back on - easier, simpler and cheaper to use the Dc Charger - note this is not a 24v to 12v converter .

I already have a 12v meter in the system but if 12v is not charging I would like a light to come on immediately to alert me when there has been a failure - just like it does if the alternator has failed.

I am well aware of other various options but hoping someone can give me a lead on how to replicate the ignition light from an alternator.

Thanks

Garry

[lsemmens]

What about something like a normally operated relay that drops out if 12v disappears.

[garrycol]

What about something like a normally operated relay that drops out if 12v disappears.

Yes but then the battery powers it so nothing happens until the battery is flat. Hence my crude option of having a big arse diode to prevent power from the battery flowing back.

So if power stops from the charger and the relay kicks in as you suggest - the diode will stop power from the battery keeping power on to the relay.

Thanks for your comments.

Cheers

garry

[mtv]

Many DC-DC chargers will maintain a battery at a constant low current, so voltage output from the charger is usually constant whilst the engine is running... (depends on wiring configuration).

Your diode method sounds feasible, but to make it more reliable, you could add a voltage alarm module, which when set to a voltage just below the lowest charger output voltage, could in turn switch the alternator indicator lamp on.

The voltage alarm could be wired to a relay so that it only operates when the vehicle ignition is on, otherwise it would be switching the indicator lamp on due to no output from the charger when the ignition is off.

[porkop]

Zener diode to a LED???

[bob_m_54]

What about one of these?

[garrycol]

Thanks = that is just a battery charge indicator - I already have that readout - I am after a means of telling me when the battery is not being charged not what its actual level is (already have that).

Thanks to everyone for your input - looks as if there is not a circuit that will mimic a alternator ignition light in my system - I will proceed with a 100amp diode in the 12v power lead from the charger to the battery and connect an indicator light via a relay that comes on when the Dc charger is not charging. The diode will prevent the battery powering the relay when Dc power is lost.

Thanks

Garry

[Tom Mix]

Alt warning light is an idiot light, can be off and batt not charging ifi. Load is high. I fit dual volt, ammeter led gauge, only few $ from alibaba. At glance, batt health indicated.

[bob_m_54]

Thanks = that is just a battery charge indicator - I already have that readout - I am after a means of telling me when the battery is not being charged not what its actual level is (already have that).

Thanks to everyone for your input - looks as if there is not a circuit that will mimic a alternator ignition light in my system - I will proceed with a 100amp diode in the 12v power lead from the charger to the battery and connect an indicator light via a relay that comes on when the Dc charger is not charging. The diode will prevent the battery powering the relay when Dc power is lost.

Thanks

Garry

It will tell you when the battery is not being charged, or more correctly, when you aren't getting alternator input. If the light is not green, your battery terminal voltage is below 13.2VDC ie no alternator input. It's probably a tad low for some deep cycle batteries, where 100% charge is close to 13V, but even for them, any load on the battery will drop the voltage quickly enough for the yellow led to illuminate.