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Old 05-30-2022, 04:08 PM   #1
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Electrical question - blower fan current too high?

Hello everyone - I'm renovating my 1981 Bayliner 3270 and have a question about my under-stairs cabin heater. It has two fan blower motors (probably original), mounted to a radiator-type bus heater. They run okay, but seem to be drawing too much power.

My normal house voltage readout sits at 12.3. But when I turn on the two cabin heater fans, it drops to 11.0. As a comparison, when turning on my two engine room blower fans, it only drops to 12.1. That seems more normal.

I've pulled the unit and spun the fan blades by hand. They both do spin, but not 'freely'. When I try to spin and release, they stop immediately. They feel 'equal' to each other.

I've looked up the replacement motors for the heater and they are supposed to draw 3.6 amps max each. So 7.2 amps for two of them. It's a two-speed motor, they are $70 each, and I need two of them, so I'm reluctant to order them if I don't need them, since the unit seems to be working okay. They look like automotive heater/defroster fan motors.

Even though they 'work', I'm concerned they will draw more power than necessary when away from shore power.

So here are the questions for the electrically experienced.. is this a normal current draw for these two fans? Or are these old fan motors probably too old, dusty, tired and in need of replacement? Or is there any lubrication or cleaning I can do to possibly revive them? Or is there a possibility there is a completely different electrical issue causing this result? Bad connection? Bad ground?

Thanks in advance for all your help and advice.
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Old 05-30-2022, 04:27 PM   #2
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You seem to be trying to measure current by observing the voltage drop of your battery bank. It’s true the bank voltage will drop but in no way is it relatable to some other load. It could be the battery is shot, or there is a bad connection somewhere or the motor has a bad bearing or about two dozen other problems. What you need is to borrow a DC clamp-on ammeter (and someone that knows how to use it) and measure the current directly and compare that to the full load current on the fan motor label at the specified voltage. New cost about $50 for the very cheapest a DC clamp-on ammeter.
Another possibility is to use the DC amps measuring capabilities of a DVM. Most can measure 0-10 amps DC when properly configured. Most people do not know how to do that and will blow the internal fuse.
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Old 05-30-2022, 04:33 PM   #3
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As mentioned above you need to measure actual amperage draw to rule out a wiring issue. Many multi meters will allow you to test up to 10 amps DC. If you have a VOM read the directions to determine whether you can use it for up to 10 amps.

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Old 05-30-2022, 06:02 PM   #4
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I agree that you need to actually MEASURE the current drawn.
If there is a label on the motors look at it and it should tell you how many amps at what voltage it needs.

However, the fact the fans quit quickly when spun would indicate the motor bearings are in need of some attention and the motor a cleaning.

THe bearings are likely Oilite, a porous bronze bushing. Over time the oil dries up and gets sticky. I have reoiled them in several applications, in place, by taping one side of them and filling them from the other side with a synthetic oil which is quite thin, 10/40 or even 5/40 , in this case Royal Purple which will penetrate those porosities. Let them sit overnight , look at how much was absorbed, not leaked, and top up again. When the bearings quit absorbing the oil they are ready for use.

Then reassemble.
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Old 05-31-2022, 09:55 AM   #5
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couple of things, first, your voltage. if that's your resting voltage it probably means it's time for new batteries. at the very least you should take a hard look at the wiring and connections. also, look at your charging method. a fully charged fla battery at rest should be around 12.7 volts.
secondly, i don't really worry about the amp draw on stuff that only runs when the engine is running. (within reason) these heaters are really only putting out heat when the engine is circulating water. so if the circuit is designed properly, with adequate wire size and proper fusing, that's what matters the most to me as the alternator will provide the power to run it.
as was mentioned, a good cleaning of the motors will probably provide better performance, but might not lower the amp draw any substantial amount.
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Old 05-31-2022, 10:17 AM   #6
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I agree with all of the above. The motor bearings are probably shot. My RV furnace blower pulls about 5 amps. A 5 amp load should not pull down your battery's voltage by more than 1 volt.

But as noted above, the batteries also sound old and worn out.

So replace the motors and look at your batteries.

FWIW there is a neat and cheap shunt based battery monitor on Amazon for less than $50 that will let you know exactly how much current the motors are pulling by noting the change in amperage drawn. See: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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Old 06-01-2022, 06:45 AM   #7
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Remember that the heater only works when the port engine is running. The alternator/voltage regulator will maintain proper voltage.

Are you checking the voltage with a multimeter or the gauge at the helm? A lot of corrosion, loose connections can exist in a 41 year old vessel.

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Old 06-01-2022, 10:43 AM   #8
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YOu can measure the actual current draw of each motor separately.
I assume you have them out of the unit.

Do you have a meter that can measure 10amps? Many meters can read up to that level. Some only allow a lot less, maybe 1 or 2 amps.

If yours reads up to 10 then use it to actually check the draw. You will need some leads with alligator or bulldog clips and a battery to use to connect it to.

Even the old analogue units can be used. A DMM is not necessary as it won't matter if there is a slight difference in measuring ability. If the meter shows substantially more than the rated of 3.6 then the motors need some work or a replacement.


Check the battery voltage first though. You car would be a good source.
Just be carefull with the leads.
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Old 06-01-2022, 12:53 PM   #9
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Your motor has dry bearings.

A lot of small motors run out of lube after a few years. Most can be relubed and run a few more years before it's needed again. When the motor starts to drag from dry bearings it draws more amps, eventually burning out the motor. On the boat I have a box fan, my dad bought about 1950. Every 5 years I give it a few drops of oil and it continues to run.
Better motors have ball or roller bearings and they need grease. Sealed ball bearings can have the cover removed, greased and resealed. Back when bearings were $3 or less I didn't bother, but now that that $3 bearing is $20 I regrease.
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Old 06-01-2022, 05:54 PM   #10
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Thanks David. I have the Victron monitor on my shopping list, but this looks like a decent option.
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Old 06-01-2022, 06:19 PM   #11
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Thanks, and follow up

Hello everyone - I'm the OP on this thread. Thanks again for all your suggestions - I learned a lot (again!!)

Yes the motor bearings are probably dry - I'll try to lubricate.

Yes my 41 year old boat has many sketchy electrical connections - I'm working my way through them, including replacing the old glass-barrel fuse panels with modern updates.

Yes I have a multi-meter that will measure up to 10amp current so I will check that too.

Yes I acknowledge that a reported voltage drop is not the best way to measure current being drawn, but now that I know I can use my multimeter up to 10 amps, I'm good to go.

But here's the REAL lesson learned.. I've been reporting these voltage drops to you, as they appear on a readout attached to a small switch panel I purchased recently to control some LED lights. The voltage readout is just part of the switch panel.

And a fairly inexpensive Amazon-sourced switch panel at that..

So.. I attached my multimeter directly to the house battery bank and tried the same set of tests. Even thought the two resting voltages were pretty much the same, once I started turning things on, the two readings differed dramatically.

Turns out the cheap switchplate readout was vastly overstating the actual voltage drop. So I tried turning everything on.. all the lights, fans, etc. The switchplate readout was 9.8 volts. The batteries said 12.0

Any idea why this would be? Bad connections somewhere between the batteries and the switchplate readout? Cheap Chinese switchplate circuitry? Or is it measuring something different than what I would read at the battery terminals?

So.. my thanks again to the folks who took the time to respond. Every time I do this I learn so much!
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Old 06-02-2022, 11:05 AM   #12
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how far between the switchplate and the batteries? what gauge of wire?
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Old 06-03-2022, 03:26 AM   #13
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The switchplate is probably 10 feet from the panel. 16 guage I think. But the final couple of inches within the switchplate to the voltage readout circuitry is super thin.
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Old 06-03-2022, 08:58 AM   #14
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Quote:
Originally Posted by BrentwoodBayliner View Post
The switchplate is probably 10 feet from the panel. 16 guage I think. But the final couple of inches within the switchplate to the voltage readout circuitry is super thin.
16 awg is fairly small. i'd do a voltage drop test on it to see how much loss you have. is the blower the only thing on the circuit?
seems like a funny place for a volt meter to me. the panel meters should ideally be connected at the main distribution panel or battery terminals.
some boat owners do funny things though, part of the joy of buying a used boat is undoing all of the "less than ideal" additions to the electrical system.
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Old 06-05-2022, 02:26 PM   #15
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Quote:
Originally Posted by Bmarler View Post
...part of the joy of buying a used boat is undoing all of the "less than ideal" additions to the electrical system.
We clearly have WIDELY different views on what constitutes "joy".

But yes, you're absolutely right about the very high likelihood of having to 'untangle' what previous personnel may have attempted to do to the wiring.

For questionable power consumption issues I find it's VERY useful to have a spare bit of 14ga 2-conductor wire handy to do direct connections between a battery and a device that's having trouble.

Take the in-between wiring out of the equation and use something known-good. If the device still draws the same amperage (use a clamp meter) then you know have reasonable evidence to believe it's not the existing wiring. But if the consumption differs, then you've got a step-by-step, segment-by-segment, debugging effort tracking down just WHERE the loss is along both the +/- sides of the circuit. Could be a bad connection, corroded or loose, or could be hidden corrosion inside of what looks an otherwise OK piece of wire.

Best of luck to you!
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