Automobile battery protection

[dgbland]

Hi! This looks like an excellent forum. I have a situation on a 1986 Buick Riviera that randomly kills its battery overnight. After many years, I have finally discovered the culprit. The car is equipped with a dash mounted touch screen CRT. Within the CRT case is a relay that randomly develops contacts that stick leaving 12 volts on the CRT filament which draws 2 amps.

I have identified the battery voltage supply lead to the CRT unit. Now, I am looking for a circuit that will monitor the battery voltage and remove the 12 volt supply when the battery voltage drops below a set voltage. The circuit must not draw too much current since it must be active all the time and, therefore, must not discharge the battery itself.

This need just occurred and I am going to attempt to design such a circuit. It just seems silly to do that if such a circuit already exists. So, if anyone knows of such a circuit, I would like to see it. If I do not find one and have to design one, I will post my solution here for others to find.

For anyone interested, I cannot easily repair or replace the CRT unit. The unit was manufactured by Zenith and data (schematics) nor parts are available for it. It is no longer available. I think GM discontinued its use in 1989.

Thanks and I really enjoy reading the forum.

 

[williB]

Hi! This looks like an excellent forum. I have a situation on a 1986 Buick Riviera that randomly kills its battery overnight. After many years, I have finally discovered the culprit. The car is equipped with a dash mounted touch screen CRT. Within the CRT case is a relay that randomly develops contacts that stick leaving 12 volts on the CRT filament which draws 2 amps.

I have identified the battery voltage supply lead to the CRT unit. Now, I am looking for a circuit that will monitor the battery voltage and remove the 12 volt supply when the battery voltage drops below a set voltage. The circuit must not draw too much current since it must be active all the time and, therefore, must not discharge the battery itself.

This need just occurred and I am going to attempt to design such a circuit. It just seems silly to do that if such a circuit already exists. So, if anyone knows of such a circuit, I would like to see it. If I do not find one and have to design one, I will post my solution here for others to find.

For anyone interested, I cannot easily repair or replace the CRT unit. The unit was manufactured by Zenith and data (schematics) nor parts are available for it. It is no longer available. I think GM discontinued its use in 1989.

Thanks and I really enjoy reading the forum.

why not just connect a relay to the ignition switch , so that when the car is on , the power is available to the crt , or replace the origional relay..
ps i'll be passing by raleigh in a couple of days .. i'll wave..

 

[Sebi]

I agree with williB.
When the battery voltage monitor say "battery low" it's too lait, You cannot started the motor...

 

[tansis]

perhaps a solid state relay or mosfet circuit
may be the answer to your problem

**broken link removed**

 

[Ravi]

Perhaps you may use a "deep discharge preventer" which will prevente the BATT running down below a preset level. Many circuits of this nature are available in battery charging/monitoring links.

 

[john1]

Hi dgbland,

I agree with williB, as you have identified the feed to the
intermittent unit, i would seem an easy matter to insert a
relay so that the supply to it is cut when the ignition is
turned off.

However i would personally try to spray WD40 (or similar)
into the innards of the offending relay before doing any
thing else.

I have been surprised in the past by the effectiveness of
this rather cack-handed approach.

Cheers John