Dash Warning Light for DC to DC Charger

Submitted: Friday, Oct 09, 2015 at 13:32
ThreadID: 130552 Views:1913 Replies:6 FollowUps:5
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My vehicle is 24v though I have converted the ignition to 12v that runs from my 12v Deep Cycle aux battery. This battery is currently charged via a 65 amp alternator on the engine. I am going to change this to a 24v to 12v Dc charger.

The Dc to Dc charger has two small leds to indicate input power and output power and I could extend these to display on the dash. However lights coming on (like a normal ignition light) rather than going out if there is a charging issue more readily catch your attention.

An alternator ignition light is powered by the 12v battery and glows until the charge from the alternator matches or exceeds that of the battery and extinguishes the ignition light and ideally I would like this display setup for my system. However I am not sure how to wire this up.

Any suggestions.

Thanks

Garry

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Reply By: Member - Murray R (VIC) - Friday, Oct 09, 2015 at 22:10

Friday, Oct 09, 2015 at 22:10
Garry
You could use a redarc voltage sensing relay P/N VS12 and wire it to an alarm as in their diagram.
You would wire it to the 12 volt side of the DC DC charger so that if the charger fails it would trigger the relay and alarm. You could also wire in a relay controlled by the ignition switch in the supply circiut so that it only works when the ignition is turned on. Check it out on the redarc site as it should suit to do what you want.

Murray
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AnswerID: 591418

Follow Up By: garrycol - Friday, Oct 09, 2015 at 22:35

Friday, Oct 09, 2015 at 22:35
Thanks for that - I will look at the Redarc site.

However if the charger does fail wouldn't the voltage sensing relay just then be powered by the battery and only activate when battery voltage is reduced to the relay preset level.

Cheers

garry
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Reply By: Allan B (Member, SunCoast) - Friday, Oct 09, 2015 at 22:26

Friday, Oct 09, 2015 at 22:26
Hi Garry,

Arranging for a pair of 'reverse' repeater LED's on the dash is not difficult if you know your way around electronics but complex to provide detailed instruction for the inexpert.

An easier, and more effective arrangement, may be achieved by simply installing a digital voltmeter on the dash connected to the 12v auxiliary battery. This will not only provide indication of charging activity but also will supervise the battery's SOC when not on charge.
Cheers
Allan

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AnswerID: 591419

Follow Up By: garrycol - Friday, Oct 09, 2015 at 22:41

Friday, Oct 09, 2015 at 22:41
Thanks - I will research these reverse repeater LEDs.

I already have a digital voltmeter on the dash that monitors the 12v system but if the charger has failed it continues to simply monitor battery voltage which will only drop slowly and will be only when it drops low that I will realise there is a failure in the system.

Cheers

garry
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Follow Up By: The Bantam - Sunday, Oct 11, 2015 at 15:09

Sunday, Oct 11, 2015 at 15:09
an inline ammeter would tell you the whole story combined with the voltmeter ...... there have been a couple of combined voltmeter and ammeter uints come on the market at a reasonable price.

Check jaycar, altronics and the other usual suspects

cheers
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Reply By: Member - Murray R (VIC) - Friday, Oct 09, 2015 at 23:27

Friday, Oct 09, 2015 at 23:27
Yes it would but if you set the set voltage say .3 .4 volts lower than the float voltage of the charger that should let you know that it has failed. If the charger fails the 12 volt battery voltage will decrease hence triggering the relay letting you know that the charger has failled.

Murray
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Follow Up By: Member - Murray R (VIC) - Friday, Oct 09, 2015 at 23:46

Friday, Oct 09, 2015 at 23:46
Garry
Should have also said that the surface charge on the battery would drop off ralatively quick with some load on the battery in a short time. How many amps are drawn when you turn the ignition on and what else is drawing off the aux battery while the car is running. The bigger the load the quicker the voltage will fall.

Murray
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Reply By: Nomadic Navara - Saturday, Oct 10, 2015 at 09:34

Saturday, Oct 10, 2015 at 09:34
Quote "and I could extend these to display on the dash. However lights coming on (like a normal ignition light) rather than going out if there is a charging issue"

Easy to do. One relay per circuit will do the trick if the outputs for these lights will drive a small relay. Wire your conversion circuitry to the ignition circuitry. Wire the indicator light extensions to its relay. Wire your dash indicator to the NO side of a change over relay contact. When the chargers indicator light fails the relay will release and the NO contact will light up your warning light. (If you are keen enough you could also wire a pizo buzzer in parallel with that light.)
PeterD
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Reply By: garrycol - Saturday, Oct 10, 2015 at 15:00

Saturday, Oct 10, 2015 at 15:00
Thanks to everyone for your ideas - they have focussed my thoughts.

What I am going to try is to run a micro relay (the type that is off when has power applied) from the wiring that works the inbuilt output led on the charger. Switched power for the dash light will go through the relay so that when the charger is making power the relay will cut power to the dash light with the ignition on. If there is an issue the relay will open allowing switched power to the indicator light - when the ignition is off the dc charger is off and there is no power available to the dash light.

However the on fault is that that if the system is working the the dash light will never light up so I will not know if the globe/led has blown. I will use a time delay relay to actually switch on the DC charger when the ignition is switched on so the dash light will illuminate until the charger is switched on by the time delay relay.

I appreciate the advice provided - it has been very helpful.

Garry
AnswerID: 591436

Reply By: duck - Sunday, Oct 11, 2015 at 08:12

Sunday, Oct 11, 2015 at 08:12
Just for interest, my isuzu nps 300 had 5 x redarc bc to bc 24volt to 24v charges they just kept failing the 6th one was built for my truck & now seams to be working fine the std bc bc charger that can run 24v to charge 12v has not mist a beat.
AnswerID: 591449

Follow Up By: garrycol - Sunday, Oct 11, 2015 at 11:53

Sunday, Oct 11, 2015 at 11:53
Thanks - I am wary about changing to the DC to DC charger from my alternator because of possible reliability issues so I have two small 24v to 12v converters that I can still run the ignition from and leave the battery to recharge from solar.

My charger is an OEX 60amp charger so with only one battery and some other electrics to run it should not be running anywhere near max capacity and that should also help with reliability.

Cheers

Garry
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