voltage limiter part number

[hemi68charger]

Does anyone have the limiter part number? I'm here at work and don't have my parts book....... Trying to see if I can order one............

Troy

[Plumcrazy]

Have you thought about building an electronic limiter?

Cost me about $5 in parts at Radio Shack.

[hemi68charger]

Have you thought about building an electronic limiter?

Cost me about $5 in parts at Radio Shack.

Can you point me to a link or something?... I just priced a new one from MaMopar and it's $65 !!!!...

Thanks....
Troy

[Plumcrazy]

Check out this site.  http://www.martinihenry.com/temp/instrumentreg/instrumentreg.html

What I did different was that I didn't solder the wires to the circuit board.  I used the male terminals from a couple of old extension cords and just plugged them in where the voltage limiter goes.  I mounted limiter chip where the original capicitor attached to the cluster housing, the housing is metal so it should make a good heat sink.

Use Radio Shack's voltage limiter #276-1770 and a couple #272-1027 capacitors.

[hemi68charger]

Hey Paul...
Looks easy enough, except I'm a little confused on the wire connections.. Looks like the black is the middle prong which is ground. The capacitor obviously goes to the "black" ground, but in the illustrations, I can't tell which one of the red or green wires it's connected to.......

Troy

[DanishDude]

If anyone is interested, then I wouldn't mind at all making an 'illustrated guide' on how to do this modification properly. The original article skips quite a few important details in regard to mounting and component selection IMHO, and the original circuit can easily be improved by adding a single component, thus enhancing long time reliability.

The assembly shown in the color photos contains a grave mistake I'm afraid, plus a few general minor ones as well.

Frank 'Ask Me About Electronics'. 

[Plumcrazy]

This may help.

The top slot in this photo is ground.
The middle one is the 12v feed.
The bottom one is the 5v output.

[hemi68charger]

This may help.

The top slot in this photo is ground.
The middle one is the 12v feed.
The bottom one is the 5v output.

Thanks.   

But I was looking to see which prongs the capacitor marries with on the limiter at the component end of the modifications.... From the pictures from the article, it's hard to see......

Troy

[hemi68charger]

If anyone is interested, then I wouldn't mind at all making an 'illustrated guide' on how to do this modification properly. The original article skips quite a few important details in regard to mounting and component selection IMHO, and the original circuit can easily be improved by adding a single component, thus enhancing long time reliability.

The assembly shown in the color photos contains a grave mistake I'm afraid, plus a few general minor ones as well.

Frank 'Ask Me About Electronics'. 

Any additional information is always welcome......   Thanks.. 

Troy

[DanishDude]

Any additional information is always welcome......   Thanks.. 

OK, hang on. I need to go make a few snapshots.

[Plumcrazy]

This may help.

The top slot in this photo is ground.
The middle one is the 12v feed.
The bottom one is the 5v output.

Thanks.   

Troy

I don't have a picture but here's my best description.

You have the voltage limiter chip with 3 terminals.  Ground, 12V input and 5v output.   The package it comes in will show you which is which.
You need 2 capacitors. Each will have 2 leads.  One of them will be marked by a black stripe, that's the negative lead.

Attach 1 of the positive leads from each capacitor to the 12v feed lead on the limiter.
Attach the negative lead from one of the capacitors to the ground lead of the limiter.
Attach the negative lead from the other capacitor to the 5v output lead of the limiter.

Then attach a wire to each limiter terminal and run them to the correct slot on the circuit board.

I used shrink tubing at all the connections.   Also I encased the capacitors and limiter with some glue to keep the terminals from breaking off the limiter.l

[DanishDude]

OK, here are my comments and suggestions in a somewhat abbreviated form. I'm not sure just how much detail people are interested in, so please feel free to ask for clarification as needed.

*) The core problem with this modification is longevity of the components involved. Under and below the dash, just next to the firewall, the temperatures are of course often anything but a comfortable room temperature. This means that we must take pains to rate everything ridiculously conservatively when making DIY modifications. It is better to spend a few bucks too many than having to tear out the dash again in the not too distant future IMHO.

Circuit:

*) I have added a power resistor, 3.9 ohm / 25 watt, in front of the voltage regulator. The total power dissipated by both circuits will be the same, but this will help spread out the heat generated, thus lessening the heatsink requirements for the IC regulator. The resistor also to some degree help to protect the IC and the first capacitor from voltage spikes generated elsewhere in the car's electric systems. Photo 1.

A 25W rating is quite a bit above the maximum expected dissipation of 4W, but in a hot environment the next smaller standard size, 15W, may be too small. Additionally there are easy to bolt on aluminum clad resistors in this power rating available. These are made by Welwyn and others. See photo 2 below and look for the pair of power resistors, both anodized a bright orange. Photo shows 10W units though.

*) The first capacitor must have a voltage rating of at least 25V and more is preferable. I'm not even sure where the author of the article has the 15V figure from, since the closest standard is 16V. A 16V rating is OK for the output cap.

*) Input cap should have a capacitance of 100 micro Farads (uF) or larger to have any serious effect on transient suppression. I would probably use at least 1000uF here. The output should be 10-100uF but no larger to avoid a nasty problem with lockup of the regulator at power-on.

Components.

*) The voltage limiter is an industry standard 7805 voltage regulator in a TO-220 case. Any ever so small electronics parts shop worthy of the name will have these in stock. Price is around 50 cents (US) in quantities of one.

*) The type of capacitors used are known as 'electrolytic capacitors' if people need to ask for them. They are available with two different physical layouts of the leads, axial and radial. Photo 3. There is no difference in function and either may be used. Depending on how people intends to assemble the voltage regulator, it might be useful to know the options available.

*) Electrolytic capacitors are available in many different quality grades and for use at different maximum operating temperature. Apart from time, then high temperatures are the single most important factor affecting longevity. Note that when electrolytic capacitors die, they sometimes 'explode' with a large pop and spreads the corrosive chemicals within on the immediate surroundings. Not something I want to happen behind my dash.

The most common temperature ratings are 85 and 105 degrees Centigrade. Capacitors are rated in Centigrade everywhere, including in the US. Running a low quality 85 deg. C component at elevated temperatures may result in an expected lifetime of only a few hundred hours, worst case. Read: It might be worth finding and paying a premium of a few cents a piece for high quality 105 deg. C capacitors...

It may be possible to spot the different temperature markings on the capacitors in photo 3.

*) The small heatsinks shown in the photos in the article are way too small. The larger one shown in the color photos is a bit more to my liking, but I cannot help wonder if it will be enough. Remember that the fins should be vertical when mounted in the car to allow a better airflow due to convection.

*) There are small and correctly shaped heat conducting silicone pads available for mounting between the 7805 and the heatsink at a cost of 5 cents or so. Use them, they help even out any irregularities and air pockets between the 7805 and the heatsink. If the silicone pad starts to visibly deform as the 7805 mounting hardware is tightened, then the torque used is excessive and should be reduced.

Assembly.

*) Rule #1: Solder is not glue, nor is the bond a welding!

The strength of a solder joint is nowhere comparable to that of a weld or a good epoxy glue, and solder will develop cracks and fracture when subjected to a combination of elevated temperatures, strong vibrations and mechanical torque from unbalanced components.

As an unbreakable rule in a high vibration environment, then a construction must not fall apart in any way if we imagine every scrap of solder was somehow instantaneously removed from all joints! Consider yourself warned.

What this means is that:

1) Wires soldered to the back of the printed circuit board should be secured with a small drop of silicone sealant after soldering and cooling. Preferably a bit away from the solder joint, so it can be inspected and repaired if required.

2) All wire and component lead junctions should be bent and mechanically joined by twisting etc. before solder is applied.

3) Capacitors should also be fastened with silicone or in a similar fashion to relieve the strain on the solder connections. Again a tiny drop will be sufficient, and it will still be easy to remove if required.

Also see freehand wired ex-military electronics for more on this.

*) Since high temperatures kills the capacitors, they shouldn't be mounted directly at or on top of the hot voltage regulator. Placing them a few inches away, say on the back of the printed circuit board, is perfectly OK.

*) The resistor can be located anywhere convenient and preferably cool, the lengths of the connecting wires are completely unimportant.

*) Something like a 35W soldering iron will be ideal for working on most wiring on a car. I mostly use a 25W unit, but it is sometimes a bit on the cold side for complex junctions. A 100W unit as suggested by the article will be way too hot most of the time. One risks ruining the printed circuit board when doing the connections on it, since the copper traces lifts off quite easily when hot. The components will not enjoy the experience either.

*) The wire bundle from the regulator IC going to the circuit board should also be fastened to the surface with silicone sealant or in a similar way, as previously mentioned in this thread. The leads from the IC are quite fragile where they exit the black epoxy moulding and will break off if subject to too much torque or shear.

*) Soldering wires and component leads freehand is done by:

1) Clean component leads and circuit board pads as needed with fine carborundum paper or similar. (This was forgotten in the color photos referenced above.)

2) Strip insulation from hookup wire, twist and tin the exposed copper strands. Photo 4.

3) Mechanically join hookup wires and component leads by forming with needlenosed pliers etc. Photo 5 & 6.

4) Solder. Since everything was already cleaned and perhaps even pre-tinned, this will be quite easy. Photo 7 & 8.

5) Optional but recommended: Cover all exposed solder joints with heat shrink tubing. May require a bit of planning ahead.

6) The next time I see some goofball on TV 'tag' the electronics together  with a soldering iron when restoring a multi-kilobucks car, I'm gonna scream...

Frank.

[DanishDude]

The last photos.

[ChargerRob]

How much would you charge me to make one for me. 

[DanishDude]

How much would you charge me to make one for me. 

Joking aside, then I wouldn't mind lending a hand if we lived a bit closer to each other. Realistically I feel this is something one needs to do with full access to the car. If I attempted to make a finished unit, chances are good that it wouldn't physically fit and would foul with something important.

...and I like your '69 as well. 

Frank.