The International Cessna 170 Association

Hi all—

I've been very busy fixing many of the issues on my plane I've asked for help with on the site, but my ongoing electrical problem is troublesome.

I have a 55 170B model with a new 20 amp generator, new 20 amp regulator, and brand new battery.

However, when I have my radio, transponder, and just nav lights on (LEDs), I get a negative deflection even at full power. When I have ZERO electrics on, I have only the smallest positive deflection. This means during night flight with my landing lights, nav lights, strobe, cockpit lights, radio/trans I'm at a HUGE negative deflection on my ammeter, even at full power.

I met up with Charlie yesterday who gave me some great advice to run a ground wire from my battery to firewall. I currently have a ground wire from my battery to accessory case.

What are everyone's suggestions here—bad wire, bad ground? Thoughts?

Are you sure that small positive reading on your amp meter isn't just the natural resting place of the needle when there is not power in the system? It sounds like your generator/regulator is not working at all. Did you flash the regulator? This procedure needs to be done in order to have a generator and regulator work after they have been disconnected from each other. Oh yes, more than occasionally you don't have to flash the regulator but many times you do. I don't have the time to tell you how to flash the regulator but it is easy. See these instructions: viewtopic.php?f=26&t=4854&p=42449&hilit ... tor#p42449

Also if you are going to fly around with landing lights, nav lights, strobe, cockpit lights, radio/trans, your 20 amp gen is not going to keep up. Maybe if you have LED landing lights it will.

He has a new generator. Tried two different regulators, but we did not flash them. His negative battery terminal goes to the engine, and he has seaplane bushings on the firewall. I suggested the ground wire as I could not see any straps around engine rubber mounts. At full rpm I measured only 12.8v at fuse bus. Seemed low to me?

The most common failure of the generator system is loss of polarization. This can happen when the regulator is changed...when a new battery is installed...anytime the electrical system is “jump started” or other major event to the system.

“Flashing” the regulator/generator is the “old timers” phraseology.... What you are doing is “Polarizing”.... restoring the polarity of the field-coils in the generator so they retain residual magnetism... by momentarily exciting the field-shoes the field windings are wrapped-around. The easiest method is to turn the Master switch ON...do NOT start the engine...and use a paper-clip or jumper wire or etc to momentarily connect the regulator ARMature and FIEld terminals to each other. You’re DONE. Start the engine and run it up to high idle (1700+) and you should have a charge.

GAHorn wrote:...“Flashing” the regulator/generator is the “old timers” phraseology.... What you are doing is “Polarizing”.... restoring the polarity of the field-coils in the generator so they retain residual magnetism...

Anyone who’s actually done it knows why “flashing” is a fairly appropriate term for the procedure.

12.8v is definitely low for your charging voltage. double check that at the battery to make sure you don't have a problem between the battery and circuit breaker as well. your charging votage should be close to 14.25v. If it is only 12.8v at the battery it will never get a full charge and possibly cause other problems as well. You should also have additional ground cables to the one you mentioned. Engine to mount, mount to airframe, or engine to airframe. Inspect all grounds for possible corrosion.

And last be sure the regulator is grounded.

I 'flashed' the regulator and it fixed the problem.

I'm now getting 15V at full RPM with zero electronics on. Then, with all my lights/radios on I'm getting 12.8V.

To my understanding, as long as it's above 12V I should be OK in flight? Even if the ammeter is showing a discharge...?

reecewallace wrote:I 'flashed' the regulator and it fixed the problem.

I'm now getting 15V at full RPM with zero electronics on. Then, with all my lights/radios on I'm getting 12.8V.

To my understanding, as long as it's above 12V I should be OK in flight? Even if the ammeter is showing a discharge...?

Assuming your ammeter reads zero when the master switch is off, and it’s wired correctly (shows discharge when systems are turned on without the engine running), the answer to your question is NO. If the ammeter is showing ANY discharge, it means that the electrical system is consuming more current than the generator is supplying, and the battery is making up the difference. The battery will eventually deplete under those conditions.

Charging voltage should be 13.7 to 14.7, depending on battery temperature.
http://www.gillbatteries.com/Content/PD ... manual.pdf

DaveF wrote:Charging voltage should be 13.7 to 14.7, depending on battery temperature.
http://www.gillbatteries.com/Content/PD ... manual.pdf

E2B5DBE8-69E1-4EC1-8EB8-9C6DAE0702A8.jpeg

And, that voltage is measured at the battery, not downstream somewhere like the cigarette lighter, through an unknown number of wires and terminals, each with an unknown resistance.

The fully charged battery cell voltage is 2.2v times 6 cells on your battery, that equals 13.2v fully charged with no load. The charging voltage needs to be above that. the 13.7v - 14.7v that dave's chart reflects is in line with That, The 14.25v value I gave is average temp value. Your battery is a "source" of electrical power when its voltage is greater than that of the generator like when you are on the ground with master on and engine not running. With your engine running and your generator generating 15v, it is the higher voltage and the 'source' and your battery is an electrical "load". The point I'm trying to make is that your battery cannot be discharging unless it has a higher output voltage than the generator and it isn't possible for your battery to be above 15v. your generator is either not putting out 15v in flight or your ammeter indication is in error.

When you say all your lights, you are including your 2 landing/taxi lights? And these incandescent or quarts?

If both answer are yes, this is your issue. If you have the 4509 bulbs , each of them pull nearly 8 amps from your system. That only leaves 4 amps for everything else. This is why you are seeing 12.8v and a discharge with this load. You can not continuously run your landing/taxi lights. Turn them off. You should see a positive amp charge and your voltage should go up to an acceptable range.

cessna170bdriver wrote:

GAHorn wrote:...“Flashing” the regulator/generator is the “old timers” phraseology.... What you are doing is “Polarizing”.... restoring the polarity of the field-coils in the generator so they retain residual magnetism...

Anyone who’s actually done it knows why “flashing” is a fairly appropriate term for the procedure.

It’s really not necessary to do it Naked.

FredL wrote:The fully charged battery cell voltage is 2.2v times 6 cells on your battery, that equals 13.2v fully charged with no load. The charging voltage needs to be above that. the 13.7v - 14.7v that dave's chart reflects is in line with That, The 14.25v value I gave is average temp value. Your battery is a "source" of electrical power when its voltage is greater than that of the generator like when you are on the ground with master on and engine not running. With your engine running and your generator generating 15v, it is the higher voltage and the 'source' and your battery is an electrical "load". The point I'm trying to make is that your battery cannot be discharging unless it has a higher output voltage than the generator and it isn't possible for your battery to be above 15v. your generator is either not putting out 15v in flight or your ammeter indication is in error.

The “spirit” of FredLs’ comments are good but there are technical issues with it. Voltage is similar to water-pressure in pipe. For current to flow into a partially-depleted battery the output of the charging system must have a higher voltage. However, an Ammeter measures Amps...not voltage. Amps are similar to “gallons” of water in that pipe...flowing in the direction of the lesser pressure.

Reece, You should perform an “electrical load” analysis of your airplane. Take all of the loads (appliances) demands and add them up. If they exceed the 20A capability of your charging system (generator/regulator) then you will have a discharge of your battery. In that case you have a choice to make: Either reduce the load by turning off some equipment (such as landing/taxi lights) or increase the capacity of your charging system (by upgrading your generator/regulator to a higher-capacity system such as a 35A gen/reg set-up ($400) or convert to an alternator system. ($1500). (estimated materials cost, labor will be extra.)

Keep in mind that only FULL TIME loads are usually considered when conducting an electrical analysis. Landing and Taxi lights are “Intermittent” loads and not considered full time. It is commonly accepted that full-time loads should not exceed 80% of generating capacity. This means that your full-time appliances should not add up to more than 16 Amps with your current 20A system.

You are a Member of the Assoc’n. You rec’d a free copy of the Electrical Systems Service Manual authored by an Idiot but can be downloaded free from the Members Only page of this website. It will give you a basic understanding of the system and how to Troubleshoot and correct any Problems.
It is unlikely based upon your description, but possible, that your regulator needs adjustment and the manual also tells how to accomplish that. Do NOT attempt that until you have performed your electrical analysis and told us your results, IMO.

GAHorn wrote:

cessna170bdriver wrote:

GAHorn wrote:...“Flashing” the regulator/generator is the “old timers” phraseology.... What you are doing is “Polarizing”.... restoring the polarity of the field-coils in the generator so they retain residual magnetism...

Anyone who’s actually done it knows why “flashing” is a fairly appropriate term for the procedure.

It’s really not necessary to do it Naked.

One of your better efforts, George!