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MG MG Y Type - Running with no battery

Should a Y-type or any car of it's age be able to run without a battery? My ammeter reads negative at idle and from what I've been told this is normal. If that's correct, then how is there enough electricity to create a spark?

I ask because the two times I've cranked my YB when the battery was flat, it died a couple minutes afterwards and I couldn't start it again for the life of me. I assumed it was because the battery had just enough life in it to supply voltage to the coil, but when it reached "empty" the car could no longer sustain enough spark.
Steve Simmons

If you join up the battery leads ( battery removed) and can spin the engine over fast enough to get dynamo to generate enough voltage to get the cut-out in the control box to cut-in, it will run. How ever, there is a serious problem the dynamo initially needs the battery to boost its electro-magnets to start with!!!!

The negative reading on the ampmeter simply means that electrical power is coming FROM the battery, and not charging it as a positive reading would show.

If the ampmeter reads nil, the battery voltage is balancing that produced from the dynamo.

Neil.
Neil Cairns

By that logic I assume that the generator cannot produce the same power at idle that the battery can supply, but that the amount of power it does produce is sufficient to allow the car to run? However with the battery installed the car uses additional power from the battery. Can I assume this means the car will run stronger at very low RPMs with a battery versus no battery?
Steve Simmons

Steve - As long as there is enough voltage available to the coil to produce a strong and reliable spark (ususally at least 10 volts), the car will run. additional power from the battery (or anything else) will not produce a stronger running engine. Dropping below the voltage that produces the strong, reliable spark will, on the other hand, stop the engine from running entirely. The purpose of the battery is to produce enough voltage to keep the engine running properly and, secondarily to produce enough current for short periods to turn the starter over while keeping the required voltage to start the engine. The purpose of the generator is to replace the power in the battery (simplified explination) that is being used by the engine and auxiliaries. Even though it is possible to run the engine with the generator alone, without the battery, this is not the purpose or intended use of the generator, nor is it a proper test of the generator. As Neil stated, if the ammeter is indicating in the negative direction (and assuming that it is relatively accurate) it is indicating that the battery is being drained faster than the power is being replaced by the generator. This is a normal situation at idle, but once the RPMs are up around 1500 - 2000, you should see the ammeter move into the positive direction, indicating that more power is being provided to the battery than is being drained from it.

There are a number of things that can cause the batery to go flat over time. First the battery may be worn out or have a shorted cell. A automotive electrical shop can check the battery and tell you if it is any good or is holding a charge properly (by automotive electrical shop, I am not talking about the local discount store with the batery tester, but not the expertise to give you a decent analysis of what the tester is telling them). The second thing that can cause a problem is a sick generator, although if it will drive the ammeter into the positive direction while driving, it is probably good. The final item in the equation is the control bor or regulator. If it is not controling the generator properly, this will contribute to a flat battery. Again, a good auto electric shop can test these items as a system and tell you what is good or bad.
Good luck - Dave
David DuBois

What then would be the cause of a drain on the battery during idle? If the engine will run without the battery and you have no accessories powered then the car should not need anything from the battery, correct? Why then would the ammeter show a drain? Not trying to argue the point, just to understand it. Thanks for the info - it's very interesting!
Steve Simmons

You probably have a leak to earth somewhere on your car. A good auto electrician should be able to trace this for you - I can never be bothered to do this myself!

Paul
Paul Barrow

Steve - The generators are very RPM sensitive and at idle it is not producing sufficient current to supply the demand of it's own field coils and the ignition coil. Even at speed the generator in your YA, if it is original is only putting out a maximum of 17 amps. Even if it is the later generator for the late TD/TF, the best you will get is 19 amps. Secondly, the control box may be malfunctioning to the point where you are not getting anything out of the generator at idle. Paul is correct in saying a good auto electrician can check everything out and determain if you have a problem.
Good luck - Dave
David DuBois

The voltage regulator is functioning perfectly now that Jerry Felper adjusted it. I'll look for a ground issue.

David, so is what you're saying that the generator may actually pull power from the battery to supply it's coils with the amount of energy they want, and that this doesn't significantly affect the output which supplies spark?
Steve Simmons

Yes - the generator field coils require a small amount of current from the battery/charging system in order for the generator to work. No, this does not affect the output of the coil and it's ability to produce a spark until the system voltage goes below aproximately 9 - 10 volts. The ignition coil also requires a certain amount of current to operate, all of which will cause a negative swing of the ammeter if there is insufficient current being produced by the generator to overcome the amount of current being drawn. This can happen at idle because the generator is not turning fast enough to produce much current at that time. This condition is normal and as long as the generator is putting out sufficient current during the time you are driving at higher RPMs, it will make up in charge what was lost during idle. I have driven approximately 40 miles one time with lights, heater, and wipers going on my MGB and with the generator not working at all before the voltage dropped far enough to stop the car. This is why I said earlier that one of the things that can cause the symptoms that you are experiencing (flat battery after the car has sat over night) can be caused by a battery that is not taking or holding a charge. This is something that a auto electric shop can check for you. It can also be caused by bad battery connections, or a weak generator (since you say the regulator is functioning correctly), bad connections at the generator or something that is miswired and causing a current draw when the ignition is shut off. I have even had a battery run down by the clock that had stopped in a current on condition (although it took about two weeks to drain the battery. Good luck - Dave
David DuBois

Battery is brand new so that isn't what's draining it, and the clock doesn't work although it may still be using voltage. I have a wiring harness on order anyway so perhaps it will clear itself up when I'm through rewiring the car.

I wonder if this drain is the reason that the car, both times I have crank-started it, only ran for approximately two minutes before stopping and refusing to start again without charging the battery. Maybe there was just enough power left in the battery to make up for the drain on the system for a short time but the car cannot run at low RPMs without a battery attached. I'll have to test this theory when I get a chance. I figure all I have to do is get the car running and then pull off the hot battery lead.

Thanks for all the info and for bearing with me. When something interests me I am known to crave a full understanding of it even if the technical details are outside of my range of mechanical knowledge. I still want to learn more about how a car such as the Y-type can run with no battery despite the fact that it will draw power from a battery when attached. It should be a fun group of weekend experiments!
Steve Simmons

Steve. No car fitted with a generator will idle without a battery because the generator is incapable of providing enough power to keep itself and the ignition going at low revs. If you keep the revs up a bit it will keep going. The battery shows a drain at idle because it is supplying the power that the generator cannot. A sick battery may not be able to supply enough power to either the starter motor to turn the engine fast enough to start or, more importantly, provide enough power for the ignition. The starter, when turning slowly, is little more than a dead short on the battery and will pull the voltage down to below the level at which the ignition system can cope. 6-8 Volts is not uncommon under such circumsances and this is nowhere near enough. The ig. system takes very little power though so as long as it has enough Voltage, say, around 8-10 it will work which is why a push start will work even with a bad battery. One trick in the old days was to wire an auxiliary battery, say a motorcycle battery, to power the ig. only so that a poor main battery did not pull the voltage which the ig. requires down.
ian thomson

Curious... did the old Model T and such cars have batteries or did they use another method of powering the ignition system?
Steve Simmons

Steve

Hand crank to start, magneto for ignition, and kerosene for lamps.

FWIW


Larry
49 YT
Larry Hallanger

Wow, that makes sense. I wonder if anyone ever burned their car down with kerosene? :) Thanks again for the info!
Steve Simmons

Steve - A couple of other thoughts. YOu can test the generator for proper operation by disconnecting it from the regulator and the battery (disconnect the wires from both terminals on the generator) and short the two terminals together. Attach a voltmeter, set to read around 25 volts, between the shorted terminals and ground. Start the car, but keep the revs low (1000 or less). Watch the meter while increasing the revs. The voltage should rise rather quickly. Keep the revs limited so that the voltage does not go above 20 volts. As long as the voltage raises above 12 volts and continues to rise, then the generator is good. If the voltage will not go up above 12 volts or even if it goes to 12 volts and stops, not going any higher regardless of the RPM, then the generator needs to be rebuilt. Note - it is very important not to let the voltage rise above 20 volts as it will go up very quickly above that point and will result in a damaged generator.

Another area to look at if your battery is not charging is the battery cables. They can develope corrosion under the insulation that will cause high resistance and cause al sorts of problems, including not charging the battery.

You mentioned that you are going to be replacing the wiring harness. I would strongly recommend that when you do, you clean all ground points (including the one for the battery and the engine) to bright metal and then coat the cleaned area with a conductive, anti-corrosion surface compound such as Kopr-Shield, a product made by Thomas & Betts (P/N 201-31879). This can be purchased from electrical outlet houses like CED or Stusser's or from Eastwood. I would imagine that it, or something similiar is available from Agent Orange (AKA HOme Depot) or Lowes. This will provide a good contact for the ground wires and keep the connections from getting corroded in the future. An easy way to clean the ground points is to get a piloted wire brush to put in your drill. These brushes are available from MCM <http://mcmdirect.com>. The part numbers are: 3/16" pilot 00063586 and 1/4" pilot 00063594.

One futhrer item in regard to the generator. Many generators on the T series and Y type cars, MGAs and early MGB are damaged by running the fan belt too tight. This is especially true of the T series and Y type cars because of the large cross section belts used. Following is an article that I wrote in conjunction with another local Register member regarding the fan belts and the correct ones to use.

KEEP YOUR BELTS LOOSE
(DON’T BE SO UPTIGHT – LOOSEN UP)
by Dave DuBois AND Stuart Locke

All of you who have been around me for any length of time have heard me preach about keeping the fan belt on the T series cars loose. A tight belt will do really bad things to the generator (kind of like what over tight underwear does to a person, but that is a subject for other publications), like causing excessive wear on the rear generator bushing and in severe cases, actually wearing through the bushing and into the housing. It also causes sloppy water pump bearings and water leaks according to Stuart Locke, who has rebuilt numerous generators and water pumps for people that keep their belts too tight. The same thing is true for the MGA and the early MGBs that use generators rather than alternators. I have always followed my own advice and kept the fan belt in our TD EXTREMELY loose. So you can imagine my surprise a couple of months ago when I traced the source of squeaking in the engine compartment to be the generator armature rubbing on the field poles because the rear bushing was worn excessively. I pulled the generator and did a quick overhaul, cleaning it up, replacing the rear bushing and brushes and repainting it. Then I started puzzling out why the rear bushing wore so quickly (if you consider 15 years to be quick). Interestingly, at the same time I was working on an article, Stuart Locke was doing the same thing some 600 miles south in Sunnyvale. His article arrived about two days after I had given mine to Liz for the Bonnet, so after consulting with Stuart, I am combining the two articles

Since the fan belt that was originally on the car when I bought it in 1974 was a bit over sized, I had replaced it when I restored the car in the early 80s. At that time the belts from Moss were a solid and very stiff belt, but I didn’t give that much thought at the time. In revisiting the situation after rebuilding the generator, I took a more critical look at the belt I had been using and dug around until I uncovered the original belt (the one that was too long). What I found was that the original belt was a Gates Green Stripe belt that was segmented on the inside edge and was, therefore, a very flexible belt. When installed, it could be run very loose and as a result, put very little sideways pressure on the generator pulley, which results in very little pressure being transmitted to the rear bushing through the armature. I then embarked on a search for one of these really flexible fan belts and through trial and error and a very helpful auto parts store in Bremerton, who special ordered goodness knows how many different sizes of belts for me from Seattle, found the proper size Gates Green Stripe II belt. This belt is also segmented on the inside surface. Although the segments are much wider than on the original Green Stripe belts, it still results in a much more flexible belt than what I bought from Moss. The part number on this belt is TR22392 and it is a 11/16” X 39 3/4" (17mm X 1010mm) Truck and Bus series belt made by Gates. In his article, Stuart tells us that the Goodyear 22394 belt is 22/32” X 39 1/2" (17mm X 1005mm) and that the Moss belt is not only very stiff, but is also considerably shorter at 17mmX 925mm (about three inches too short), which I found when I was special ordering all those belts trying, to find the right one. Additionally, Stuart found in a 1949 book, Exploring Auto Mechanics by Harold T. Glen that the fan belts on the TCs and TDs (and by extension, the TFs) should be adjusted to have ONE INCH of slack between the generator and the water pump (not on the longest leg as we are used to).

By the way, as I said earlier, the same problem exists on the MGAs and early MGBs, but is not so pronounced since they use the later style narrow fan belts which are much more flexible than the ones used on the T series cars. The fan belt still needs to be run quite loose (one half inch of slack between the generator and the water pump, rather than on the longest leg) on the MGAs and MGBs to prevent premature wear on the rear generator bushings.

My source for the belts over here in Kitsap County is Westbay Auto. Those of you in Seattle, Tacoma and other areas will have to check around for the Gates belts or Stuart tells us the Goodyear belts are available from Skip Kelsey (Shadetree Motors Ltd) at 925-846-1309. So now you have no excuse not to loosen up and get comfortable.

Please excuse the length of this missive.
Good luck - Dave




David DuBois

Great article, David. I'll look for the belts you suggested. It's about time to do it anyway. As for the battery, it does seem to charge but not as quickly as it discharges. There must be an issue somewhere because it drains even while not in use. For now I may install a battery cut-off switch.
Steve Simmons

A cut off switch is always a good idea. If you can find somewhere to hide it put it in the earth (ground) connection and it will add to security by making the car impossible to start by shorting the ignition straight to the all too accessible battery.
ian thomson

My YB had a cut-off switch fitted when I bought it. Very clever: mounted to the bulkhead/scuttle so its spindle protrudes into the glovebox. So whenever I leave the car alone for a longer period, a mysterious twist of my hand in the glovebox will make sure power is really "off". And the looks remain unspoiled. Probably the restorer of 20-odd years ago had fitted this device when he had dismantled the interior of the car, the installation of it necessitating removal of the dashboard.
To the ammeter question: Mine shows negative when idling, more so with lights on etc, which seems logical, but not positive when running at higher rpm, just stays stuck in the central position, or occasionnally very, very little (1 mm) into the positive section of the dial. On the other hand, my battery is always well charged. Would strong positive current only be shown with a discharged battery gobbling up electricity?
Remo Peter

Perhaps your gauge is not calibrated correctly?
Steve Simmons

I would expect 10-20 Amps charge just after starting dropping to 3-5 Charge after 10-15 miles when the battery recovers the charge it lost during starting. This will show less charge and take longer to recover if anything is switched on at the time. It also takes longer when cold. This assumes a good battery and charging system and a properly calibrated guage. If the guage is stuck in the centre and doesn't move far to the positive side I would suspect the guuage first.
ian thomson

This thread was discussed between 30/11/2003 and 05/12/2003

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