volt meter vs amp meter

[AUSMHLY]

Now that my car is finished, and I use that term loosely, I would like keep my eye on the electrical draw while I'm driving.

Still positive, with a generator.
Headlight have halogen bulbs.
Rear reflectors have 10watt halogen bulbs.
Garmin navigation system and two pairs of 15 watts each computer speakers with fuses on all, tapped into the ignition wire.

Everything seems fine, but it may be best to add a meter that shows what's going on.

Should I add a 30+ 30- amp gauge or a volt gauge. If a volt gauge, what numbers on that?

Then I'll need to know what size wire and where to tap into.

Oh, and where should I find these gauges. Been looking at the usual places, petboys, kragen, autozone, etc, with no luck for the 30 amp gauge.

Thanks in advance, Roger

 

[Keoke]

Hi Roger

To locate the gauges search British sport car gauges.

In the interests of safety, economy and simplicity use a volt meter.--------------------Keoke

 

[GregW]

Hey Roger,
I bought a couple gauges off ebay. Searching for “Smiths gauge” and “Smith gauge” will get different hits. Here is one of each amp and volt gauge. I went with the voltmeter gauge for reasons 1 and 3 that Keoke mentions.

 

[BobHorvath]

A volt meter will tell you (some what) where your system is and an amp meter will tell you where you are headed. You might want to consider what you are running on a regular basis. Headlamps 15Amps (that is a guess), heater 5 amps and all other including the garmin plus I assume radio, speakers, & ignition perhaps another 7-10 amps. You are probably near the max of your charging system. The gauges will not help except to tell you when to turn somthing off. The generator (if that is what you have) can maybe put out 30-35 amps. The amp meter will tell you if you are keeping up. A 30 amp gauge may do the job but A 50 would also and you may be going to an alt where the 50 would be required. I would put in 10 ga wire. I am in Mexico right now so I will have to look @ a wiring diagram when I get home before I suggest a location to splice into same. Keoke is correct in suggesting the volt meter for all the reasons stated. If you take his suggestion you would also have the idiot light that may come on under way if the charging system can't overcom the load.

 

[roger_abbott]

You may want to consider taking the current load off your ignition switch wire and the switch itself by using a solenoid to carry the current directly from your battery to your various added devices. That way, you don't have to replace the car's original wiring to the ignition switch. Of course, the solenoid is wired to the ignition switch to close when the ignition switch is on.

 

[anthony7777]

bog, i like your idea of the solenoid a couple of seperate fuses would probably also help. /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif

 

[Keoke]

bog, i like your idea of the solenoid a couple of seperate fuses would probably also help. /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif

Better give that some more thought 7777.---Keoke

 

[anthony7777]

keoke, sounds to me his car is still a "fuse virgin", considering hes adding "various other items" whats wrong with adding various other fuses, unless your objecting to the use of the solenoid? /bcforum/images/%%GRAEMLIN_URL%%/shocked.gif p.s. had to pick up a n.o.s reverse gear for the transmission rebuild yesterday lyn and virginia looked exceptionally pleasing. wish i could transmit a good bronx cheer. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

 

[BobHorvath]

If you use a solenoid, which is a good idea, make sure you use a continous duty design.

 

[Keoke]

If you use a solenoid, which is a good idea, make sure you use a continous duty design.

Whats good about it maybe I missed something?---Keoke

 

[Dave Russell]

Hey Bob,
Maybe it's a terminology problem. A "solenoid" is generally considered to be an electromagnetic actuator. Converts electric signals to mechanical motion.

Are you are talking about a relay? Please excuse me if I'm confused.
D

 

[BobHorvath]

The solenoid I am referring to is a ferrite core that slides within a magnetized cylinder. Much like a starter solenoid on the Healey. The solenoid I have on my Healey is designed for high current not continuous duty and it has a high holding current. A continuous duty solenoid has a lower over-all current rating but also a lower holding current resulting in less current draw and thus is less apt to over heat. Solenoids are more often used in an inductive load application like a starter. An inductive load arcs as the voltage collapses upon disconnect. A relay is usually a magnetized ferrite core that when energized pulls down on a plate called an armature. Contacts close and away you go. In this case, Dave you are correct in suggesting a relay as the load is not inductive. So an enclosed automotive relay is perhaps best.

 

[Ed_K]

Hi Roger,
I may as well give you my 2 cents worth, now you may have enough cents to buy one of those volt meters, which is what you should use instead of an amp meter in my opinion. If you can get a black faced Smiths gauge off of ebay, it will look like it " belongs " in your car. As said by others, one side to frame ground. the other to a wire that only has voltage when the ignition switch is on.
Ed

 

[Keoke]

The solenoid I have on my Healey is designed for high current not continuous duty and it has a high holding current.

And so what in the world are you using this brutish item for and what good is it?


An inductive load arcs as the voltage collapses upon disconnect.

True but its inrush current is much higher and potentially more destructive to other circuits.



In this case, Dave you are correct in suggesting a relay as the load is not inductive. So an enclosed automotive relay is perhaps best.


This is not the case. In most cases a relay is used to;

energise and deinergise an inductive load. To wit: the lowly "Horn Relay"

---------------------------------Keoke-?

 

[BobHorvath]

The one I refered to on my Healey is the starter solenoid (high current, high induction and no contact bounce). The in-rush on a coil, such as a solenoide or a relay is curent not voltage and therefore should not cause damage to any device on the load side. When the solenoid is switched off @ the key all loads connected to this lug on the key will see a voltage spike as the field in the solenoide or the relay colapses. For this application your suggestion is a good one all electronic devices such as powered speakers, radio & possibly electronic ignition should connect to the load side of either a relay or a solenoid. All other resitive loads such as lights should not be bothered by the collapsing coil

 

[Keoke]

The one I refered to on my Healey is the starter solenoid (high current, high induction and no contact bounce...---We all have one of them so whats new!


The in-rush on a coil, such as a solenoid or a relay is cu rent not voltage and therefore should not cause damage to any device on the load side.----Ah Yes as I said it be current.However you, cannot produce a voltage with out current flow,and in an inductive circuit the faster the current flows the higher the voltage produced.



When the solenoid is switched off @ the key all loads connected to this lug on the key will see a voltage spike as the field in the solenoide or the relay colapses.



Very little since this voltage is not DC and the high reactance of the small wire will attenuate it significantly.


For this application your suggestion is a good one all electronic devices such as powered speakers, radio & possibly electronic ignition should connect to the load side of either a relay or a solenoid.

All other resitive loads such as lights should not be bothered by the collapsing coil

Then why does every smart car use a headlight relay? Because this is a good way of isolating the circuit from transients, provides for less voltage drop in the circuit as well as relieving the switch of the need to switch the high current in the circuit.---Keoke-?

 

[roger_abbott]

I guess I should have said "relay" when I said "solenoid". Some people equate "solenoid" with the starter relay or solenoid.

I used a 30 amp relay from Radio Shack, catalog item 275-226, list price $6.49. It draws 160 millamps at 12 volts, so its current draw when energized is almost imperceptible. It is rated at 30 amps continuous load. It weighs a couple of ounces.

It worked quite well for me. My headlights, heater blower and radio all go through this solenoid - er - relay, bypassing the ignition switch wiring.

 

[GregW]

It worked quite well for me. My headlights, heater blower and radio all go through this solenoid - er - relay, bypassing the ignition switch wiring.

In a stock wiring harness, don’t the headlights and radio bypass the ignition switch anyway? /bcforum/images/%%GRAEMLIN_URL%%/crazy.gif

 

[roger_abbott]

GregW, actually you are right. The headlight circuit does not go through the ignition switch. It comes directly from the regulator. I did not insert a relay in this circuit in my Healey but on another car where the light switch was well worn and the contacts iffy. Sorry for the error.

 

[GregW]

No worries Roger. I’ve been leery of the headlight wiring. I bypassed the regulator connection and routed the headlights to their own fuse in the fuse box.