Author Topic: 798 c volt meter  (Read 8943 times)

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Offline Rocketman783

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798 c volt meter
« on: May 19, 2010, 11:20:22 AM »
Kind curious about why my depth finder does not show the correct voltage. When I measure the voltage in the head plug I get 12.74 yet the depth finder will show voltage as 11.8. After I run the charger on the battery  and turn the charger off my volt meter shows 13.37 but my unit will show 12.2 or some number like that. No matter what the depth finder  is always off by about one volt. Same thing for my 788.


Offline keizerh

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Re: 798 c volt meter
« Reply #1 on: May 19, 2010, 01:10:33 PM »
Had the same with 987 and 1197 unit.
Thought that Dutch voltage was different to US voltage  ;)

hendrik
« Last Edit: May 19, 2010, 01:11:50 PM by keizerh »

Offline sonar2000

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Re: 798 c volt meter
« Reply #2 on: May 19, 2010, 01:11:06 PM »
We see this with other products also.  I think that the internal voltage is after the drop of supply internal to the unit and not the external supply. Various GPS and other sonar units do this also. 
Chuck

Offline Rocketman783

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Re: 798 c volt meter
« Reply #3 on: May 19, 2010, 04:38:38 PM »
That is what I thought.

Offline mendota

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Re: 798 c volt meter
« Reply #4 on: May 19, 2010, 05:35:12 PM »
The units are reading correctly - the lower voltage is due to the resistances of your wiring, connections, and fuses.

You will notice quite a bit less error if you turn your backlight down, for instance.  Makes a 0.4V difference with my 1197.

The error is inherent in their measurement technique.  They SHOULD have a compensation scheme, however.  Even a simple voltage offset would be better than nothing...........

Offline Rocketman783

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Re: 798 c volt meter
« Reply #5 on: May 20, 2010, 07:23:11 AM »
I assume you are refering to the electronics inside the unit, since I measured the voltage at the plug end that the unit connects into and it measures almost exactly the same as my actual battery within .02. It would be more useful if it read the actual  battery voltage comming into the unit.

Offline mendota

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Re: 798 c volt meter
« Reply #6 on: May 20, 2010, 09:49:27 AM »
Well, when you are measuring at the plug end, I assume that it is not plugged in to the unit, and the unit powered up.  Pretty hard to get at the wires under those circumstances - you would need to pierce the insulation.

You are just measuring the open-circuit voltage at the plug, which tells you virtually nothing - because the voltmeter presents a negligible load, and therefore there is no voltage drop from the wires and connections.......

I would suggest that if anyone is seeing more than a volt difference between the actual battery voltage and the display, they should definitely check their wiring, as the resistance is higher than it should be.

Offline sonar2000

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Re: 798 c volt meter
« Reply #7 on: May 20, 2010, 02:35:01 PM »
The wiring is probable ok.  There is a diode in the unit betweent the external supply lead and the inside of the unit where the unit makes the voltage measurement. this will cause about a 3/4 volt drop.   
Chuck

Offline Humminbird_Greg

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Re: 798 c volt meter
« Reply #8 on: May 20, 2010, 03:32:09 PM »
I believe that we are still compensating for the diode voltage drop Chuck (we had a problem with this a long time ago...).  I checked six different model units myself (700, 800, 900 and 1100 series units) and found each within 0.2VDC of the input voltage.  Used a calibrated digital volt meter to ensure accurate readings versus what the units showed.  My guess is that the voltage difference he is seeing is due to the unloaded versus loaded states he was measuring in (checking voltage at end of power cable with no unit attached versus checking the unit displayed voltage when powered up or “loaded”).  This shows that there is some type of current restriction in his power circuitry as it is drawing the voltage down to compensate.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline stillbear

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Re: 798 c volt meter
« Reply #9 on: May 20, 2010, 07:12:47 PM »
Rocketman my 997 basically reads the same thing yours doe's that is with a brand new battery
new dedicated circuit to the battery with marine tinned wire.Obviously there is nothing to worry about because they all read the same way.  Gary

Offline MonteSS

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Re: 798 c volt meter
« Reply #10 on: March 07, 2011, 11:10:52 PM »
Has this problem been fixed? Or are only some units affected?

All of the above statements dont sound right. The voltage readout on the unit should read the battery voltage. Period.

My 898 reads 12v. I installed two new batteries (in parralell) that freshly charged show 12.9 v each. Something is not correct with the unit. I also checked at the power plug to the unit and get 12.9v.

What gives???

....Bill


Offline Ddorriety

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Re: 798 c volt meter
« Reply #11 on: March 08, 2011, 05:59:46 AM »
I just went through this with my unit. The unit is measuring the voltage correctly.
It is indeed a voltage drop. I was getting approximately 1 volt drop. I measured
a 0.5 volt drop across the in line fuse holder and 0.2 volt drop across the accessory switch
on the boat switch panel. I assumed the balance was from the wiring. I up sized some of the
smaller wire to a 16 gauge and replaced the quick disconnect terminals. I replaced the fuse
and cleaned the fuse holder. In total this resulted in a 0.5 volt improvement. I plan to replace
my fuse holder when I get a chance.

 

Offline MonteSS

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Re: 798 c volt meter
« Reply #12 on: March 08, 2011, 11:20:16 AM »
Voltage is not be affected by two small of wireing. Current would be. I did professional car stereos and know a little about wiring.

The wire going in to the unit measures currect voltage. The unit displays wrong. It is a problem with the unit, or design/software of the unit. Not the wiring.

Thanks....Bill

Offline sonar2000

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Re: 798 c volt meter
« Reply #13 on: March 08, 2011, 11:36:24 AM »
Unless the "switch" or "fuse connection if slip in or bayonet type" has a resistance due to poor connection,
Then some volts would drop at that point.
Make sure all connections/connectors that are not soldered are clean and free of corrosion.
I would measure at each connection point with the positive lead of the meter. Leave the ground or minus side of the meter on the neg of the supply.
chuck
 

Offline xSilmarilSx

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Re: 798 c volt meter
« Reply #14 on: March 08, 2011, 02:29:36 PM »
Voltage is not be affected by two small of wireing. Current would be. I did professional car stereos and know a little about wiring.

The wire going in to the unit measures currect voltage. The unit displays wrong. It is a problem with the unit, or design/software of the unit. Not the wiring.

Thanks....Bill


You seem to skip some important information about wiring in this case..

Since unloaded circuit will always show a good voltage at it's terminal point,
Which is your case.
Since all cable have a "resistive" function that varies with the length and gauge of cable, if you try to pull to much current in a cable that have a higher resistive standard, you will have a voltage drop across the cable under load that you will not have in the unloaded state.

If on top of that you use poorly designed fuse holder (spring type) and shoddy crimps connectors that are not soldered on the cable, you add more "resistive" contact points that will further add to your voltage drop.

Good electrical connection is important in the 12V DC world. Since a voltage drop of only 0.3 can mean a good amount of AMPs wasted in cables/switch/connectors.

Just to make you an idea, 10 ft of 18 gauge cable, supporting a 1 Amp load will show you a 0.2V drop across the cable, not counting the connectors.

20 ft of 14 gauge will be 0.1V

Offline MonteSS

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Re: 798 c volt meter
« Reply #15 on: March 08, 2011, 10:17:55 PM »
If I measure volts with a good voltmeter at the batterey I get 12.9 fully charged. If I then measure at the power plug going into the unit, I get 12.9. So why is the unit showing way off. Obviously using an external voltmeter shows the wiring is fine. The 898 shows the wrong voltage, and it seems I am not the only one to have this problem.

I will remove the voltage reading from the readout. Would have been a nice feature though.

...Bill

Offline xSilmarilSx

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Re: 798 c volt meter
« Reply #16 on: March 09, 2011, 03:24:30 AM »
You didn't read my post.....

With NO LOAD attached at the end of your cable, it's normal that you have the SAME voltage reading as the battery...

Now, as you seem good with electricity, just plug a turn signal bulb (around 20 watts, which should provide you with a load of 1.6A) on the end of your Humminbird power cord. And then measure the voltage across the bulb terminal. With LOAD, you will not have the same voltage.

This is what you have to do to test your connection.
Don't blame a company if you didn't test it correctly!!

Offline ITGEEK

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Re: 798 c volt meter
« Reply #17 on: March 09, 2011, 07:47:32 AM »
Anytime you add load to a battery the voltage is going to drop.
The only reason that you can even see a voltage reading on your unit is because it is powered up (hard disk spinning, backlight lighting).  There's no way the voltage at the unit is going to match what is at the battery or at the power connection wires.  Unless, the voltage shown at the unit is just a calculation and not an actual voltage reading.

Here's something else to think about:
  What quality is the volt meter you are using, and what quality are the volt meters inside the Humminbirds?

It's actually better to show the loaded voltage, because this is what the unit is really working with.  You will also be able to spot a bad battery more easily this way. A bad/burnt-out unloaded battery can show 12.5 volts and drop to nothing when a load is put on it.

Offline mendota

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Re: 798 c volt meter
« Reply #18 on: March 09, 2011, 10:08:26 AM »
I disagree - the unit SHOULD read the battery voltage, because THAT is the critical quantity.  It does me no good to read 11.9V at the unit, indicating a near-dead battery, when my battery is a perfectly functional 12.6V.

The technique to compensate for voltage drop in the wiring is well known, and HB SHOULD implement software IR compensation for their voltage readout.

We do this routinely in the battery charging world.  The major variability in current draw for their units is the backlight level, so the software would have to compensate using the backlight level and a user-variable wiring resistance.

Really, pretty trivial stuff to program, and absolutely critical in 12V systems.  I've always been disappointed with HB over this, as it shows a lack of technical savvy you would expect of a company that wants to be a leader.

Offline ITGEEK

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Re: 798 c volt meter
« Reply #19 on: March 09, 2011, 11:38:51 AM »
But here's the problem.
Electricity travels in a circle.
In order to read the battery voltage, the unit must be on and working properly, and thus drawing current.  So, the current draw is part of the electrical loop which allows the unit to read the real-time voltage.
Real-time loaded voltage will always be lower than static (no draw) voltage.

The amount the voltage drops on the battery depends on how many amps it's drawing and also on the condition of the battery.  HB could work in a how many amps draw algorithm, but they don't have any idea the condition of someone's battery.

All the 12.6 volts is showing you is that your battery is fully charged.  It does NOT indicate that you have a GOOD battery.  The true test of a battery is a load test.

A bad/poor battery will drop the voltage very quickly.
I've read that 10.5 is the magic voltage.
If a 12 volt battery drops below 10.5 volts under a reasonable load, it's bad.  It doesn't matter if the battery started off at 13 volts.

Offline MonteSS

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Re: 798 c volt meter
« Reply #20 on: March 09, 2011, 12:43:50 PM »
I do not want to know if I have a good or bad battery. I know they are good and want to know the state of charge. I want to know how much longer I can fish without over discharging them.

Just did a test. Unit off at the plug I get 12.75v. Turn unit on (batteries under load) I get 12.72 at the plug. Unit reads 12.1v. Just not sure why you dont see the problem here.

Thanks for the advice everyone....Bill

Offline sonar2000

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Re: 798 c volt meter
« Reply #21 on: March 09, 2011, 02:37:46 PM »
The only reliable way to tell if a battery is good or bad is to have it tested by a devie made to determine a battery condition by varying loads. Volt meters do not do this. Battery level displays do not do this.
All the level indicator on your unit will do is let you know if the supply voltage drops. It is your responsibility to check the level on the unit periodically to see if a drop is indicated since you turned it on thus showing a discharge beyond the usual. Ort you could set a level alarm to let you know when the supply reaches that setting...
HB could build a battery tester into the unit but the cost would go out of the price range for most users.
Anyone who has a boat or watercraft will have the batteries(s) checked at least once a year and if during the year experience slow cranking or some other unusal indication have the battery checked then.
Or you could invest in a battery load tester.....
Chuck
« Last Edit: March 09, 2011, 02:39:17 PM by sonar2000 »

Offline Ddorriety

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Re: 798 c volt meter
« Reply #22 on: March 09, 2011, 09:12:22 PM »
Bill,
The point is if all the components between the battery and the unit are in good condition
and the wire is properly sized the voltage drop will be negligible. HB could never anticipate
what corrosion you may have on your terminal ends for example. These voltage drops are caused
by weaknesses is your power delivery. To find the source of the voltage drop or drops simply measure
the voltage across each component with your unit on and measure the drop. For example place one lead from your voltmeter to the supply side  of your fuse holder and the other lead  after the fuse holder if the meter reads 0.5V then  the fuse holder is contributing 0.5v drop to the total voltage drop. Do this at all the suspect points like terminal connections, switches etc..  If you have a run of small wire check across it
as well. Once you identify the problem the solution will be easy. You may want to goggle Ohms Law,
after a little study it will become clear. I hope you follow through, if you do instead of being disappointed
you will please with the outcome.

Good Luck!
Dennis


 

   


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