Thread Number: 41868  /  Tag: 50s/60s/70s Vacuum Cleaners
Hoover Model 51 - AC current through metal body?
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Post# 442267   5/26/2021 at 20:39 by BetaM64 (Pennsylvania, USA)        

Today I've been working on my Hoover 51 a bit. Usually when I'm working on these vacuums, I'll check if there's a current running through the body with my multimeter. This time, this check paid off. There's 12-14 volts of AC running through the body of this vacuum, and from experience (not with this machine), that is enough to feel.

I've come to the conclusion that the motor is not properly isolated from the metal body, but I'm not sure how to go about fixing that aside from designing a whole new rubber gasket that covers much more of the motor.

Has anyone else had this problem with this vacuum, and if so, how did you go about fixing it? If I end up not being able to fix it, I'll probably sell this one really cheap, un-restored (even though the rest of it is technically "restored), since I don't want to sell something as restored if it has enough current going through it that you can feel.


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Post# 442271 , Reply# 1   5/26/2021 at 22:45 by huskyvacs (Indiana)        

huskyvacs's profile picture
It looks like it has a new cord put on. Check there first. Mr. Jerry Rigg himself might have missed something, connected a wire wrong, or pinched a wire when replacing the cord. That leads into the next check, inspect any and all original wiring for cracks, breaks, worn spots, or if a wire is being cut into by the body. Also if it has one of those old style screw-down replacement plug ends with the cardboard or plastic insulator disc, make sure those are snug and correctly wired too.

Non polarized appliances and electrical items will be grounded to the chassis on the neutral leg of the wire, and when there is an issue with the hot side being wired into the wrong spot or shorting to the frame, it will send stray voltage through the chassis and anything metal (also happens if some part of the device in question has a damp spot on it)

A similar situation on a larger scale for me being that my garage has the wiring miswired backwards at the subpanel, so hot and neutral are reversed. Every outlet is wired correctly, but outlet testers all report back a miswire. Anything with a metal frame and especially vintage power tools will get a bit painful when wearing anything other than rubber shoes. With modern electrically protected appliances and tools, this is no sweat as they are designed to be safe from that happening and divert the stray current to something other than the chassis. But using any older appliances or tools that are non polarized will give you a tingly feeling more or less equal to if you slept on your hand. Nothing too drastic.

No need to change the design of the vacuum or add anything to it, as many people have vacuums here this old and older with no electrocution hazard, it's just there is somewhere inside it that is bleeding current that needs to be traced out. Another theory that it could be the armature windings are shorting to the motor housing and motor mount in some way, which is then shorting to the vacuum chassis. If you do have to add anything it would likely be just little rubber grommets under some of the screws.


Post# 442272 , Reply# 2   5/26/2021 at 23:13 by BetaM64 (Pennsylvania, USA)        

Thank you for the reply! The cord looks original (the vacuum itself looks hardly used), so unless it was replaced with a newer Hoover cord, I'd say it's probably original. I did test the voltage with the cord plugged in (without the motor in place) and it read in at 1.3v AC, which is a normal and unconcerning amount of bleed.

Regarding the mounting screws...there are actually none that directly mount the motor. The motor is mounted between two rubber gaskets (front and back) that seem to aim to separate the motor from the chassis. It seems like Hoover was aware of the AC current through the motor and made an attempt to mitigate the issue.

The motor itself has 80v AC going through it, so I'm certain the current is jumping somewhere from the live line over to the motor, like you suggested.

Another thing I just thought of is that there were some fine metal shavings in the vacuum (how they got there, I have no idea)... actually, that may be the whole problem... That would explain why there's so much resistance between the different points I tested. I'm not sure why that didn't send up a red flag while I was working on it. I'll just need to clean that motor off (and the housing) REALLY well.


Post# 442273 , Reply# 3   5/26/2021 at 23:20 by BetaM64 (Pennsylvania, USA)        

Slight correction:

When I mentioned the motor has 80v AC going through it, I meant through the frame, not what's being delivered to the brushes and then commutator. The brushes are getting 120v AC.


Post# 442276 , Reply# 4   5/27/2021 at 01:14 by Lesinutah (Utah)        
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lesinutah's profile picture
The uk made hooversthey have I forgot exactly what but I believe a tv or radio wire. It makes it so the vacuum doesn't blow the tv or radio. It's weird as heck but it could be something similar coming off the coil and it's grounded running through the body.

Post# 442277 , Reply# 5   5/27/2021 at 01:27 by MadMan (Chicago, IL, USA)        

madman's profile picture
A megohmmeter would really be the thing for this. You could just test the motor and all the different bits for leakage.

Here's an idea. Bring the machine into your bathroom. Plug it into the GFCI outlet (that you should have to prevent bathroom users from making toast while taking a bath). See if it trips the GFCI just by running. If not, short the metal body to a good ground (use the outlet, plumbing can be unreliable). That'll tell you for sure if, and under what conditions, you are having ground leakage.

Remember it's entirely possible the motor windings are shorting to the core.

If you're getting 12v, get a car light bulb and try to light it up with the ground leakage. If it lights, you really have a problem - like a partial short. If it doesn't light, it might simply be excessive capacitive leakage.


Post# 442278 , Reply# 6   5/27/2021 at 01:31 by MadMan (Chicago, IL, USA)        

madman's profile picture
Adding to Les' comment - *does* this unit have a radio noise suppression capacitor? (That's what you meant, Les.) If so, snip that old cap out. IIRC, some vac motors had the cap as almost part of the motor, as opposed to being a separate piece. Like permanently mounted to the motor frame. Worth investigating.

Post# 442280 , Reply# 7   5/27/2021 at 02:24 by BetaM64 (Pennsylvania, USA)        

A megohmmeter is something I'd really like to get in the future, and would make it much easier to find the source of the problem... Fortunately, this one doesn't have a noise suppression capacitor!

I will try those things out, thank you for the suggestions!

I have a strange feeling that whatever metal shavings I found may be a possible culprit. I cleaned the larger debris out and wiped down the motor briefly, but think it may need an alcohol bath with a scrub brush.


Post# 442291 , Reply# 8   5/27/2021 at 11:39 by BetaM64 (Pennsylvania, USA)        

Welp, turns out I'm stupid; hopefully anyone else who runs into this problem sees this thread and comes to the same conclusion as me!

Basically, that voltage reading I tested on the chassis means nothing. I've been doing a lot of reading, and the voltage is only really half of the equation, the current is what matters in this scenario.

How did I figure this out? I took a look at one of my other vacuums, a Hoover 700, and measured its voltage while it was running. It had 80v AC all the way up the handle, and I know I've touched this handle before, so when I touched it with my hand and the multimeter at the same time, the voltage plummeted to 1.5v AC.

The same thing happened for this canister. The voltage plummeted to 1.5 volts as soon as I touched it.

This is yet another reason I wish I'd have gone to school for electrical engineering!

Anyway, moral of the story is, if you measure the voltage coming off your vacuums' metal chassis, it will NOT tell you if your vacuum will shock you. And, furthermore, the canister is fine.

I feel like I've done the poor thing a disservice now, so here's some glamor shots! It's only missing a few attachments (aka all of them except the crevice tool)!


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Post# 442310 , Reply# 9   5/28/2021 at 01:14 by MadMan (Chicago, IL, USA)        

madman's profile picture
That's what I was trying to tell you. I guess I didn't explain the technical side of it. It's probably all either capacitive leakage or induction, either way, as you put it, current is what matters. And there being no real connection to power, and only minimal capacitance and inductance, the power source (the chassis) has no juice behind it to move current.

Electricity's a funny thing.

Anyway, that's why I recommended the GFCI, they trip based on current. The light bulb, too, an incandescent bulb would only light with a considerable current.





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