The place for technical discussions about GA and flying.
Forum rules: Technical discussions about GA only, please.
By thegasguy
#1560715
I have changed out my very very old B and C alternator
for a new model (200G) due to bearing failure.
The new one is up rated, to 12 amp from 8 I believe, and it came with a new regulator.
The replacement now comes with a crowbar over-voltage device and a warning lamp, all wired in and tested as far as possible.
So far so good.
But, now I get the ( Grand Rapids )EMS warning light coming on at anything under 1500rpm and sometimes at any revs, and the 'voltage' reading flashing to indicate an out of parameter issue.
It reads that the voltage coming into the EMS is 12.5 volts, which it doesn't like. When it raises to 12.6V or so it 'satisfies' the EMS and the light flashes regularly or goes out by itself.
Putting a load on by turning on the landing light has no effect, which suprises me as it's a big old fog lamp.
I'm told 13.5V. Is the proper charging voltage but there is no adjustment I know of.
The battery has started the engine ok on the 4 flights ( duration 4.5hrs) so far and doesn't seem to be going flat.
Any ideas?
I might be able to go into the settings and lower the trigger point for the EMS under-voltage warning light but is the 12.5 volts going to damage my battery?
Local opinions vary widely, any help would be appreciated.
By cockney steve
FLYER Club Member  FLYER Club Member
#1560770
Sounds like your regulator is low output. "12v" is nominal, the actual voltage should be 14.2 for a "12V " lead-acid battery. when loaded, eg starter -drain or all the toys switched on, without the engine running, the surface-charge on the battery-plates will be used and the voltage will sink to 12, or lower. A lower charging voltage than 14.2, will not recharge a flat battery, it will merely replace the surface-charge,but not deep-charge the plates. unfortunately, batteries of this type leak internally (self-discharge) which is why you should give a trickle-charge at least 3-monthly on an unused battery. The generator is regulated, as a fully-charged battery would otherwise allow the charging-current to split the water-content of the electrolyte into oxygen and hydrogen....a reason why you should avoid sparks I have personal experience :oops:
(mig-welding near a bench-charged battery which was bubbling away, fully charged.) The bang is very loud and the bits of battery-casing and acid droplets travel a fair way.. Your battery will not be damaged as quickly by undercharging, but it's capacity and service life will be shortened. Overcharging can buckle the plates and cause shedding of the active paste from the plates. In extremis, you'll boil away all the distilled water, leaving the plates dry, apart from the lower portions sitting in concentrated sulphuric acid, -well, that which hasn't been expelled with the cassing and coated the airframe/bodywork!

hth.
By johnm
FLYER Club Member  FLYER Club Member
#1560819
Aircraft systems are usually described as 14 volt or 28 volt and that represents the approx. alternator output with a 12volt or 24 volt battery, so your regulator has too low an output as CS indicates.
By thegasguy
#1560938
Thanks, another experienced guy has PM -ed me the same message.
It's a bit odd, it's all solid state and brand new. However, the evidence seems overwhelming.
I'll contact the supplier and get his opinion, and possibly a replacement regulator.
By cockney steve
FLYER Club Member  FLYER Club Member
#1561012
First make sure all your connections are sound, especially where framework is used as an "earth" return. A firm, tight connection, EG to the engine casing, upon dismantling, can be found to be badly oxidised on the contact-surfaces-this may not show up with an ohm-meter continuity-test! clean with stainless or brass-bristle wire brush and smear mating surfaces (including cleaned threads, nut-faces, washers,etc, with petroleum jelly (aka "Vaseline" at several times the price)-It's conductive) reassemble, measure volts across battery.-around 13v....when cranking, expect a drop to ~10 V
When running and charging, expect ~ 13.5, rising to ~14 as the charge-rate drops off as the voltage rises on the plates.
As remarked before, an alternator will not fully recharge a deeply discharged battery. if the regulated output was higher, it would try to" boil "away the water-content of the electrolyte, overheat the battery and possibly buckle the plates.....If you're brave/careful, competent, you could check the output all through the charging circuit to find if there's a high-resistance joint somewhere....or, as I suggested, start by cleaning the battery-terminals and clamps and work back to the alty output and "ground" terminals (ground is normally casing, via mounting-lugs) cleaning and re-making.
Solid-state is normally very reliable, but don't forget the warning-lamp circuit,as in some designs, this can have an effect on the reg.
By thegasguy
#1561084
The aircraft has been just been totally re-wired by a LAA inspector, with the addition of an earth bus bar, so I'm tending to think that it's not a poor connection issue. I managed one flight with the old alternator after the re-build and there was no undervolt warning on the EMS.
That original B and C unit was so old it didn't have the warning light, so I wouldn't have got that additional warning.
By the way, the battery is a 2 year old Gel type.
I will measure and check everything I can on Saturday to see if it indeed a fault external to the regulator.
Thanks for the comments.
#1561179
If you are driving the alternator from the vac pad drive, be aware that they act more like a dynamo and usually won't produce full voltage below an engine doing 1200rpm or so due to the speed of the rotation available from that location.

The Plane Power ones specifically advise this and I am sure the B & C is similar.
cockney steve liked this
By thegasguy
#1561393
Trent772, I agree about the low output below that threshold..
On the flights since the new alternator I have been at cruise rpm, say2350, for at least 3 hours in total and the light only goes out from time to time.
That should be 12 amps at 13.5 volts available if needed,
It comes on at lower rpm solidly.
Is it a possibility that the more powerful alternator has charged the battery right up and the EIS is seeing a satisfied battery voltage?
If she keeps on starting and running perfectly well ( as is the case at the moment ) it could be the EIS is reading low and the alt output is actually fine I suppose ?
Only a measurement at the regulator output will reveal the answer to that. Roll on Saturday.
User avatar
By Trent772
#1561497
Yes,

Start at the basics, but watch out for the propeller.... :shock:

I guess you can check output voltage from the alternator when running, checking amperage is more difficult without a clamp on meter.

You can also check voltage at the battery terminals when the engine is running - should be up to 13.8 - 14v.

Is the battery a PC680 by chance ? If so, their website has a guide for base voltage ref rough charge levels. If it isn't, you need to be seeing around 12.6v at rest across a battery, in fact, hang on.......

Right, just back from the shop. Measured our 2014 PC680 which we use for general stuff. It was 12.6v and hasn't been charged in 3 months at least.

A good place to start.
By thegasguy
#1561511
As it happens I have a brand new clamp meter in my work stuff. I'll have to check if it measures DC at 12V as well, I only use it on large 3 phase DB's usually.
I don't know the part number of the battery until I look at the weekend. It's intended use is a golf trolley and it's been really good.