This Trim Tab issue

[KnotConnected]

I.
...am *seriously*
confused.

Original issue: Bennett trim tabs were working on my '94 Larson Cabrio 280. but when they were activated, either tab, either direction, voltage dropped down to 11vdc .

Troubleshooting: I have verified the *entire* length of the harness from the pump up to the helm switches is in good shape. Cut, re-crimped and shrink tube'd ALL terminals. NO changes..

Then, I removed the harness, and using a test-harness I made, wired the pump's Red & yellow wires directly to the battery positive to activate port valve, pump reverse (lifting the port tab), and it works fine, and voltage remains at 12v. so, the pump has to be fine, and the battery has the juice to power it.

THEN, I removed the ground from the pump, thinking maybe it's weak. Replaced with slightly heavier gauge, wired back directly to battery's ground terminal (where it was before). Tested, and now the pumps don't work at ALL, and voltage drops to ~8 volts. 'EF!

SO, what I know...

*there IS 12v on the dual-rocker helm switch's 12v terminal. at it should be.

*Testing each of the other terminals on the helm switches with a multimeter, none show any voltage UNLESS the switch is pressed (working as it should..)

* +12v power source going into the helm switch comes off the ignition key switch on the helm (where it should come from, says Bennett)

*The harness is good

*The battery is good

*The ground is good (testing from battery + to the terminal on the pump is a healthy 12v

*That same engine-battery 12v power source that goes to the ignition key switch (and up to the trim tab switches) seems to be working well, as the engine cranks no issues.

the ONLY other unexplainable anomaly is that when I turn the engine battery OFF, all that stuff stops working, as I'd expect it to. ...however when testing the positive terminal on the trim tab switch with a multimeter, it shows 1/3 volt. If i shut BOTH batteries off (the other is for aux systems, lights, radio, bilge pumps, blower, etc..) the voltage goes dead. so, SOMEHOW, very slight positive voltage is still making its way to the ignition switch (which shouldn't
have any power to it.)

I'm absolutely at a loss here, so if anyone has like, *any* suggestions, or input, or ideas, I'm all ears.

thanks! (and sorry for the novel. I wanted to try to include everything I've done / concluded)

 

[Tabman]

Re: This Trim Tab issue

Ghostnode,


Take a look at the trouble shooting below

If you do step 3 right at the pump does it work?

Also please check step 6 as your boat is old enough to have one.


Here is a link to a video that covers the basic system and general troubleshooting Bennett Trim Tabs Video Player


Fluid: Automatic Transmission Fluid (ATF) any type. Hydraulic Power Unit is self bleeding, running the Trim Tabs up and down 3-4 times will purge air from the system.

Fuse: 12 volt system use 20 amp in-line fuse on positive. (24v & 32v use proportionately smaller)

Red= Port Valve
Green= Starboard Valve
Blue=Motor Forward (pump pressure)
Yellow= Motor Reverse (pump retract)
Black on HPU=Ground
Orange on Helm=Control Positive

Troubleshooting

1.If one side is not operating reverse hydraulic lines on the front of the Hydraulic Power Unit to determine if the malfunction is in HPU or actuator / hydraulic lines. If after reversing the lines symptom shifts to the other side the malfunction may exist in HPU. If the symptom remains on the same side, malfunction may exist with the actuator / hydraulic lines

2. Is the unit receiving a solid 12 volts? Low voltage will some times cause the solenoids to not open preventing the tabs from moving even though the pump motor is running.

3. Conduct the following test:
Remove the wires from the helm control and touch together as follows:
Operation=Reaction
Orange (+), blue, red= Port trim tab down
Orange (+), blue, green=Starboard trim tab down
Orange (+), blue, red, green= Both trim tabs down
Orange (+), yellow, red= Port trim tab up
Orange (+), yellow, green=Starboard trim tab up
Orange (+), yellow, red, green= Both trim tabs up

If the trim tabs function correctly for each wire grouping then the switch is at fault. Also note that any loose or missing screws on the back of the switch (whether a wire is connected there or not) can cause the pump to malfunction.

This test may also be done right at the pump by substituting a "hot lead" for orange. There is usually a connector to the wire harness within a foot or so of the pump. You want to check this connection for corrosion. You may wish to cut the connector off on the pump side and try the test on bare wires.

4. If you suspect corrosion on the wire connector near the pump, cut it out, test as above and reconnect using butt splices.

5. If you conclude the problem is in the pump, contact me. Bennett Trim Tab Systems carry a five year warranty.

6. Check to see if there is a relay in line on the wiring harness near the hydraulic power unit. If there is it is an Interrupter Relay (IR1000). It prevents the system fuse from blowing if you try to actuate one trim tab up and the other down at the same time. After you test as outlined above, try removing the relay from the wiring harness and retest the unit.(Note: the interrupter relay is no longer used in current Bennett Trim Tab systems and has been replaced with a Switches that "lock out" preventing a blown fuse).

 

[Grandad]

Re: This Trim Tab issue

Hi ghostnode. My thoughts:
1. It's normal to see a drop in voltage when a load is switched on. How much drop will depend on the size of the load and the resistance of the circuit. Resistance depends upon the size of the wire supplying the current and the integrity of all the connections, which you say are good. You've proved there is no voltage drop with a (shorter?) lead of lower resistance.
So, is a 1 volt drop too much? I think not, but if you want to reduce the voltage drop, supply the load from a larger diameter (or shorter) wire.

2. If the pumps were working, but then didn't work when all you did was rewire the negative, then your temporary wiring is highly suspect. Perhaps you disturbed a failing negative lead at the pump.

3. In regard to the 1/3 volt reading: When you have 2 batteries that share a negative return path, you essentially have a 3 wire distribution system. Turning off the positive to one battery doesn't really isolate the 2 systems or the accessories connected to them. Particularly if the negative wire is undersized for the load, you can get a "rise" in voltage when a heavy load is applied. I assume that your temporary negative is somehow disfunctional, so it follows that when voltage is applied, the current will be trying every available path back to the negative post. This path may include other accessory circuits, even idiot lights on the dash. Seeing such a voltage rise, depending upon exactly where it's measured is normal when you have a poor negative path.

It's an accepted fact that voltage "drops" over the length of a wire due to resistance. It's often readily recognized on the positive side of the load, but what is often overlooked is that on the negative wire, the opposite is happening. Under heavy load, the terminal end of a long or undersized negative connected wire will have a voltage higher than zero. So, depending upon what points you choose to measure voltage between, you'll see "normal" voltage readings other than zero or twelve, particularly with a digital meter. - Grandad

 

[04fxdwgi]

Re: This Trim Tab issue

With the voltmeter connected to the +12VDC supply to the rocker switch and a good ground, operate the tabs and read that voltage. Is it relatively steady at 12 VDC or does it drop severely? If the voltage drops when the motor is operated, you have a connection problem between the battery and the supply voltage input to the switch (bad fuse holder or connection). A bad ground between the motor and battery negetive terminal can be detected by doing the following. Try connecting the meter POSITIVE to the motor ground terminal and the meter negetive to battery ground terminal on the battery. Operate the motor. Do you see a voltage on the meter? If you do, you just found your problem, a voltage drop indicating a bad ground. If you see zero volts on meter, then the grounding is OK.

If +12VDC at the switch is steady at +12VDC, you can place the leads of the voltmeter across each device (meter + lead facing the +12 VDC supply side), being a switch or any connection and measure "voltage drop" across those points. You should read zero (or very close to it) when the switch is operated, telling you the contacts are a no (or very low) resistance connection. Any time you read a voltage across a device, such as a switch, it would indicate that the device has a resistance across it, indicating a poor connection.

After confirming you have a constant 12 VDC to the switch while the motor operates, connect your + voltmeter lead to the +12VDC supply to the switch and the meter negetive lead to the +12VDC input to the motor. Operate the motor and you should see zero volts, or very close to it. If you have a voltage indication when the motor operates, move the positive meter lead to the "load side" of the next device / connection and do it again and test. Keep doing this until you see zero voltage indication when the motor operates. When you see this change, it will tell you that the device you are connected to is the problem child.

If you know for certain that the +12VDC is constant at the supply side of the switch and you have +8VDC at the load when the motor operates, you now know you are dropping 4 volts somewhere. This indicates a bad connection or a resistance across a device / connection. Now the fun part is, finding it, but it's not very difficult once you understand how to read voltage drop in the circuit and across all connections and devices.

As Grandad stated, if one uses wiring that is too small for the run length or the load, that also will show as a voltage drop, since the resistance of the wire itself, will restrict the the current flow, showing the drop in voltage. My testing proceedure will show that too, but am thinking that the supplied wiring used on a 28' boat may be marginal for that length of a run.

Let us know what you find.