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MG MGA - Changing battery

Hi all,
I realise that there is already a lot in the archive about this.
My MGA is currently set up with the original twin 6V batteries with positive earth configuration.

I need to replace both batteries and am thinking about getting a single 002 or 202 group battery which will fit in one cradle without modification.

My preference would be to fit the battery in the nearside cradle but then I would need to extend the existing lead from the starter switch. Is there a way that this can be done safely? A quick search on the internet shows that I can get crimp splice connectors but these are not insulated.

Also, as I don't have a radio or any other electronics fitted is there any benefit in changing to negative earth? I suppose that it might make it easier to fit a charge point.

thanks

dan
Dan Smithers

Is there any particular reason you want to fit it in the nearside cradle? Unless you can re-route the battery cable so that it will reach, I can't see an easy way to extend it.

The Varta B36 battery is another option. It's the Varta equivalent of the 202/002.

Dave O'Neill 2

Thanks Dave,
The Varta B36 is one of the options that I am considering.

The only reason for the nearside cradle is weight balance as I'm more likely to drive without a passenger than without a battery. That said, it might be easier to connect a longer cable to the chassis than extend the cable to the starter switch.
Dan Smithers

After my restoration I bought two 6volt Lincon batteries as I wanted to stay original. They were expensive at around 140 the pair. A while afterwards I had a problem with them and each lost a cell. I looked at the 12v Varta B36 and as the capacity at 44AH was a bit on the low side I decided to get two and wire them in parallel. No problem in fitting in a standard tray.
Total cost 87.

My car is positive earth and I have no problem with charging. I have a charging socket let into the back board behind the drivers seat.................Mike
Mike Moore

If you have a battery isolating switch, you can just run a new cable from the hot side of the switch to the new battery location; if you don't have an isolating switch, now's the time to fit one.

I fitted the Varta battery years ago and it has been fine.

Regards
Colin
Colin Manley

Primary issue with a single small battery is reserve capacity, related to how long you can leave the lights on when it is parked, or how long you can drive it after the generator fails (and still be able to start the engine).

The BIG problem with connecting two batteries in parallel is the possibility of one of the batteries developing an internal short. When this happens the good battery will suddenly discharge through the shorted battery with very high current flow, possibly resulting in fire or explosion. If you do this each battery should nave its own fuse.
http://mgaguru.com/mgtech/electric/pics/bat_fuse.gif

Alternately you could install an isolator switch to connect only one battery at a time.
barneymg

I doubt that the weight of the battery will have any significant impact on the balance of the car. I would go for the simpler option and use the cradle on the off side. That's what I did.

I also have had the Varta battery for a few years now without any problem.

My car is positive earth and I have a charger. I sourced a cigar lighter that was made of plastic and just wired it "the wrong way round".

Colin, my isolating switch is in the earth connection cable. I always understood that was a tad safer, for example if you accidentally short the negative terminal with a spanner, etc (+ve earth) no harm is done.

Graham
Graham V

Graham
I stand to be corrected, but the isolation should be on the feed side.

I am also Positive earrh and, like you, have the charger plug wired the other way round; i.e. the on-board cigarette plug provides positive feed to the centre contact pin so as to power sat nav etc.

Steve Gyles may contribute on the double 12v set up and I recall he removed it some time back.

Regards
Colin
Colin Manley

I used to run 2 x 12v batteries in parallel and each with an isolator. I came to the conclusion that with both on line one was becoming 'lazy'. but probably it was a bit along the lines that Barney described. I only used 2 because my starting was a bit indifferent at the time and I had a spare battery from my golfing days so I thought it would be better in the car than the workbench. I eventually ran with one battery always isolated and swapped round each day. I then replaced the starter with a high torque pre-engaged version. Starting improved ten fold, primarily because high current did not then go through the rubbish starter switch. Out came the second battery and I never looked back. Would I ever put a second battery back in? No.

Steve
Steve Gyles

"I stand to be corrected, but the isolation should be on the feed side"

No good reason not to fit it in the ground cable.
Dave O'Neill 2

Colin
I think perhaps we are both right. See http://mgaguru.com/mgtech/electric/et203d.htm
Barney explains why he recommends earth cable isolation but does mention some racing groups require it in the live cable.
Graham
Graham V

My two bobs worth - I have fitted a Varta C30 530CCA 53Ah to my roadster on driver's right. This required a little mod to the battery tray - cut down each side of the rear support tray angle iron and bend down flat (C30 is correct width and height but a little long). Then fashion a new clamp from a piece of angle iron for the rear of the battery and reposition clamp bolts so they hook into the battery frame bracing rather than the normal holes - this gives the right geometry to lock the battery down firmly.
I am also a believer that the isolation switch should be on the earthing cable in case of "slipping spanners" shorting out. Also reckon driver's right is the ideal location as it is easier to procure and install a longer earth cable than extend the positive cable.
I put my isolation switch down behind the passenger seat near the drive tunnel. Also have a 12v outlet above the isolator with separate wiring that is also isolated by the isolator switch - used for trickle charging.
See photo attached (the more observant amongst you will see the battery shown is a Varta C22 - I have since this photo upgrade to the C30 - same dimensions but higher CCA and Ah rating)
Mike


Mike Ellsmore

Also having a bob each way - I not only have an insolation switch down behind the passenger's seat but also another in the engine bay located in the scuttle air vent - this is handy if you are working in the engine bay and wish to turn supply on and off. (It was there when I acquired the car so have left it there).
With all these extra connections in the system it is a good idea to check you have good connections - give the car two or three starting attempts with the coil lead disconnected and feel each joint to see if it is warm - warm is a high resistance joint and needs cleaning. You can also check voltage drop between battery positive terminal and connection post on the starter.
Mike


Mike Ellsmore

...and just for completeness my coupe has a CAMS compliant isolator switch on the hot side with an external release - isolator located in the foot well near the door hinge.
Mike

Mike Ellsmore

I have just installed a twin 12v battery set up into my MGA.
This was to see if it would improve the lacklustre starting issues I have had since installing a high compression 1950cc engine.

The single 12v battery that I used before always
struggled to turn the engine over, in cold weather although was fine once the engine was warmed up. ( Peter Morgan and Mike Maize will probably never forget the push start they had to give me on a cold March day in Wales this year!)

I installed two identical new 12 batteries but I have connected them together slightly differently to try and prevent the problems that batteries conventionally connected in parallel can apparently suffer from.

I have read that if two batteries are connected in parallel, the first battery in line tends to provide most of the power, so they discharge unevenly and eventually become mis-matched. This is what can cause the issues that Barney mentions above.

This modified connection should completely even out any voltage drop between the two batteries due to the battery cables and connectors and so they should both discharge and also be recharged identically.

I have uploaded a picture of the connections I used followed by another of the conventional parallel connections.

I still plan to regularly check the batteries to see if they still showing identical voltages to hopefully avoid any problems.

Colyn


Colyn Firth

This is a picture of the conventional method of connecting batteries in parallel.
Colyn

Colyn Firth

Thanks for all the responses.

I remember that there is already an isolating switch on the chassis side (positive) and I will run a longer cable from there to the offside cradle.

And also fit a charging socket in the board behind the seat.

Colyn, I can only see one of your pictures.

Dan
Dan Smithers

Colin, my coupe has a 1950 engine with 10.8:1 compression and uses a single 12v battery but has a geared hi-torque starter motor so has no trouble starting - so much better than the roadster with original style starter described earlier.
Mike
Mike Ellsmore

The two different pictures are on consecutive posts Dan and they seem to have uploaded ok when I open them. (I never have managed to work out how to put more than one picture on a single post)
If there is a problem, let me know and I will email them to you.
Cheers

Colyn


PS. Mike, I do plan to try out a high torque starter motor which I am informed should only need a single 12v battery.

Also, when I fitted the twin 12v batteries I noticed that it was connected by a mixture of thick and thin battery cables and so I now have replaced these with thicker cable.
However, I was underneath the car the other day and I discovered that there is also a mixture of cable thicknesses between the battery and the starter switch.

So I going to replace this with a single thicker gauge wire over the winter when I try out the high-torque starter motor.

There is always a job to do with an MGA isn't there?

Colyn Firth

Totally agree with Mike about the starter. Totally transforms the process. Which raises a point about the increased power from the double batteries going through the starter switch. Would I be correct in saying that it will accelerate burn-out (arcing) in the switch? The beauty of the system that Mike and I have is that the switch carries just sufficient current to operate the starter solenoid, not the complete battery power.

PS. For the price of the extra battery you are more than half way to paying for the pre-engaged starter.

Steve
Steve Gyles

Colin, Multiple images on one photo is a trick I picked up from Steve Gyles some years ago. Import images into a Powerpoint slide, size to fit, arrange then save slide as a jpg file
Mike
Mike Ellsmore

For people in Oz looking for hi-torque starter motors I recommend they check out the chap who advertises on our Club http://www.mgcc.com.au/wanted/sellparts.shtml
Mike Ellsmore

Apologies for slightly side-tracking your thread Dan (it is still kind of battery related) but I hope you won't mind if I ask Steve and Mike a question about the High-Torque starters that they have fitted.

I bought a High-torque starter motor over the winter and I tried it on the car. It did start the engine easily on the button but when I let go of the starter pull switch, the pinion did not fully disengage from my engines flywheel. It sounded as if the starter motor was still trying to crank the engine even after the engine had fired up.

I have been advised that the motor is maybe too close to the flywheel and that fitting a spacer should fix this.

Does anyone know if there is a ready made spacer available or do I have to make one?
(its a 5-bearing MGB backplate like Steves)

Cheers
Colyn

PS Thanks Mike for the multiple image tip, I will have to see what a mess I can get into once I blunder into the Powerpoint program :-)
Colyn Firth

Colyn

Mine is an MGA hi starter backplate machined to take the MGB seal. Sounds more likely you have the wrong driving dog for the flywheel. i.e. wrong number of teeth or wrong diameter.

Steve
Steve Gyles

A lot of people have trouble with fitting geared starter motors due to various combinations of back plates, flywheel diameters and number of pinion teeth available with the variety of MGA-MGB engine / gearbox combinations available. The supplier I mentioned above has various front flanges to suit these combinations and has an engine test rig to ensure his starters engage and disengage correctly (recently sorted a long term problem on a friend's car where the pinion was not extending enough - needed a narrower flange!). If you have the details and dimensions of your setup I'm sure he would comment on suitability if you drop him an email.
Mike
Mike Ellsmore

Thanks Mike,

I will email the address you posted earlier and see if I can get this sorted out.
Cheers

Colyn
Colyn Firth

IMHO there is a lot of myth and mystery going around about batteries and starting. Mine is a twin cam with reasonably high compression ratio, a conventional starter and a single 12 volt battery in one of the trays. It starts perfectly and unless you need large amp hour capacity to park with sidelights on for very long periods there is no need whatsoever for two batteries in parallel. The cranking amps capability of any reasonable single 12 volt battery will be adequate for starting a 1600cc engine. It's not a huge diesel engine for goodness sake!
And, Steve, the current through the starter switch is only dictated by the normal rated demand of the starter motor and not in any way influenced by having two batteries in parallel. The risk of two batteries in parallel is as Barney says - if a cell in one fails it is possible that the other will discharge heavily into it so risking overheating, etc.
So, one battery is fine - just get the engine tuning in good shape for ready starting, ensure cables are good with minimum connection joints, and check for a good solid earth conection route from battery to starter motor locating bolt. Preferably a dedicated earth cable from battery to starter bolt rather than relying on the chassis and flexible braid across the engine mounting rubber.
That's my two pennies worth!
Bruce.
B Mayo

You know something Bruce, I think your suggestion of fitting a dedicated earth cable between the battery and the starter is an excellent one!
My cars starter cranking speed has always been a bit suspect.
It had a single tiny dry cell race battery when i got it but this was hopeless in cold weather.
I switched it for a single 12v Varta battery but whilst that was better, it still didnt crank a cold engine over very briskly. (It was an 1850cc mgb motor)
It also has a starter solenoid rather than the standard MGA pull switch.

Since i have fitted the 140 bhp 5-bearing engine it has not been quite as good.
I have replaced the inertia starter motor,fitted new starter cables, new engine earth straps and checked and cleaned all battery connections on quite a few occasions.

But nothing really made a great difference

I even tried a hi-torque starter but, whilst it started fine, it wouldnt disengage from the flywheel and so it was a "non-starter"😊. Sorry😁.

So thats why i am now trying twin 12v batteries which seem to be a little better but cold weather starting in a month or two will be the ultimate test.

The extra earth cable may well be the next step.
Cheers
Colyn
Colyn Firth

Colyn
I really think you shouldn't be having the marginal performance you describe there. Whether 1600 or 1850cc, the battery/starter duty is not terribly onerous. Sounds to me like you have some unacceptable volt drops in switches, joints, connections or somewhere. The usual culprit is the earth/chasis route and a dedicated earth cable has been my first job on every old car I have owned. Always been a winner! But, if you do it, really do it! That is, as complete the route as possible - preferably with a connection from the clamp bolt on your battery (depending on where/if you have an isolating switch) to one of the retaining bolts on the starter motor. Of course this assumes you have good connections in your other polarity from battery to starter switch/solenoid to starter motor!
Bruce.
B Mayo

Colyn, If you go with Bruce's mod I would be interested to know how much improvement it made, by measuring the voltage across your battery terminals during starting attempts with both the factory earthing design and Bruce's direct cable modification (with the coil disconnected so car doesn't start).
I have not seen any local MGA/MGBs where this mod has been needed - normally a good battery and clean connections are enough.
Mike
Mike Ellsmore

Colyn, If you suspect some unwanted electrical resistance in your starter motor circuit why not measure it? You can't measure resistance directly using a standard multimeter because the values are too small. You would probably find that the resistance in the meter leads exceeds the total resistance in the circuit. But I would guess that your meter can measure very small voltages in the millivolt range. Both my digital MMs can measure in the 10mv region. So what you can do is to convert the low resistances into low voltages. You do this by passing a steady DC current through the circuit, not enough to worry about draining the battery, but around about 1-2 amps and then measuring the potential difference across various parts of the circuit.

I had a problem with my circuit after restoration and I carried out this procedure:-

I disconnected the battery earth terminal and inserted a 12v 21watt lamp in series in the ciruit. Then I clamped the starter switch in the 'on' position and measured the circuit current which was 1.6 amps. I kept this current flowing until I had finished measurements.
Then using my meter with very long leads attached to reach all over the car I connected one lead to the negative side of the battery (positive earth) and used the other lead to measure the potential difference across various parts of the circuit.
For example my first voltage measurement was at the battery side of the starter switch. This voltage divided by the current flowing (1.6A) will give you the resistance of the battery cable. The next measurement I did was to the other side of the starter switch. From this you can determine the resistance of the starter switch.

In this way you can progress around the circuit measuring both sides of the starter motor across the engine where one side of the earth strap is connected then to the other side of the earth strap and then finally to the engine side of the 21W lamp.

From these measurements you can find battery cable resistance, starter switch resistance,starter motor resistance, resistance across the engine, resistance of the earth strap and connections and finally the frame return resistance.

This helped me sort out two problems I had with my starter circuit post restoration viz a partial motor short and a poorish earth connection.
When I had sorted out my problems I found that the total circuit resistance (not counting internal battery resistance) was a mere 30-35 milliohms with the motor accounting for 25 milliohms of this and the next highest contributor was the battery cable at 2-3 milliohms.

Before I had corrected the problems I had measured the earth strap resistance at 40-45 milliohms and after cleaning up the connections this dropped to 1 milliohm or less.

The whole of the above procedure takes very little time and at the end of it you will know where your problem lies. And it might save you the trouble of making changes that are not needed.

Even though now I have no problems starting I am still a touch concerned that the battery cable resistance I measured seemed about twice that calculated for two metres of 25 sq.mm cable but that will be for another day.............................Mike
Mike Moore

Thanks Mike,
that's really interesting, I now definitely have the winter project I was looking for.

I had already planned to renew the battery cable running from the battery to the starter switch because I just the other day discovered that there is a joint halfway along from where the cable front section appears to become thinner in section. So some of my starting issues could be due to this.

I will report back after I have checked this out over the winter layoff.

Cheers
Colyn

PS You can have your thread back now Dan, Sorry :-)
Colyn Firth

Thanks Colyn.
Does anyone know what gauge cable is used for the battery connection?
Dan Smithers

Reading this thread has made me a tad anxious about the battery set up I have inherited in my 61 Coupe that I acquired last year. It is positive earth with twin 12V batteries in parallel. Coyln's earlier schematics are for negative earth arrangements so not entirely sure whether my set up (with positive earth) is the safer way or the not so safe way. Please excuse my ignorance on electrical issues but I'd welcome comment based on the attached photo. You will note that I have battery post disconnect switches on the negative posts. Thanks in anticipation. Tim


TJ Prime

Tim,
the circuit diagrams would work exactly the same in positive earth as they do in neg earth so you need not worry.

Colyn
Colyn Firth

Dan,

Battery cable having 25 sq.mm cross section will be suitable. I bought around two metres of 37/0.9mm (i.e. 37 strands of 0.9mm diameter copper). It has a resistance of about 1 milliohm per metre. I'm not sure whether the more flexible cable having many more strands of finer wire is still available but I didn't have any trouble with the stiffer cable.

TJ Have your battery trays been enlarged because your batteries look larger than my Varta B36s? If so then you must have a capacity there exceeding 100Ahour which will be great for travelling long journeys at night with your heater blowing and in driving rain!!
Have you got the same cable length in each battery leg as mentioned by Colyn? But both batteries look identical (make,capacity and age(?) and I would keep your setup.
I think the two things that shorten battery life the most are 1. leaving them in a state of partial discharge and 2. using the starter motor which is effectively shorting the battery for five seconds every time you use it leading to flaking of active material from the plates. As for safety it won't be significantly worse than when the car left the factory with far less fusing than is today the norm....................mike
Mike Moore

The best you can do with larger cables or a new ground cable direct from battery to starter is about 0.1 volt gain. Just not worth it. If you have slow cranking look elsewhere for the problem. 99% of the time it will be a dirty cable connection somewhere, but remember there are about 5 cable, 10 cable connections plus possible resistance in the starter switch. Check voltage across each connection while cranking. They should all show essentially ero voltage drop. If you find a voltage drop across any connector, stop and clean the connection joints.

When finished you should have something like 11 volts to power the starter motor, measured from the starter input post to the starter case.
barneymg

Barney mentions the starter switch. I second that. I suffered indifferent starting for quite some time. This is what I found inside that switch (see picture).

Thankfully with the pre-engaged starter only a small current now passes through the replacement switch so that degree of arcing and carbon build up is a thing of the past.

Steve

Steve Gyles

Thanks Colyn & Mike. That is reassuring. Sorry, I don't know the history of the battery trays. The car certainly never has any difficulty starting. And yes, the battery cable lengths are the same. Cheers. Tim
TJ Prime

It looks as if the back edge of the tray has either been flattened or removed to take an extra long battery, but batteries are still restrained from rearward movement by clamps. It must be quite tricky getting the batteries in and out.

Paul
Paul Dean

TJ, I note Paul's comment - I did a similar mod to the tray to fit in the Varta C30 battery (see earlier comment) but had to change the clamp rod fixing points to make battery secure. I'm interested to know if you pull up on your batteries do they remain locked down securely?

Paul, to get the Varta C30 battery in and out with the extended tray you need to tilt at about 60 degrees momentarily- no issue with sealed battery.
Mike
Mike Ellsmore

I also have to tip my single 46Ah Halford HCB063
Paul Dean

Paul. You are quite right. The rear of the battery trays has been flattened. The clamps do keep the batteries fixed in place okay but you if you pull them up from the rear they do move up about an inch. I haven't tried taking them out yet but it looks as if it should be do-able without too much difficulty if you tilt them. Tim
TJ Prime

Tim, if you relocate the rods so they hook into the joint between the tray angle support and base they will be secure even when you pull up on them. See photo i posted at start of this thread.
Mike
Mike Ellsmore

Thanks Mike. Another thing for the 'to do' list! Tim
TJ Prime

Colin,

There is absolutely no difference in the two electrical diagrams you've pictured above...parallel is parallel. Each battery shares the same amount of current so switching them out accomplishes nothing.

Gene
Gene Gillam

Gene
That isn't strictly true as in the first diagram the battery on the right has 2 additional cable hence more resistance so it will charge slower as the voltage across its terminals when charging will be lower. I agree with the short cables this affect will be low.

When I had a caravan I spent a lot of time trying to get batteries in the van or the car boot to charge which is nigh on impossible over a longish cable run. I finished doing the theoretical calculations. At 12 volts you have only a couple of volts to push charging and it hence is sensitive to any increase in wire or terminal resistance.

Paul
Paul Dean

Not quite Gene. In the second of Colyn's diagrams battery B has more resistance in series than battery A equivalent to the extra cable length of the connections so will not supply as much current.
The extra resistance is small but then so is the total starting circuit resistance. So at the end of the starting operation battery A will be slightly more discharged.

However, as soon as everything is switched off the imbalance will be corrected as battery B charges up A so it probably make little difference which way you connect them.

If the batteries are connected as in the first diagram the cable resistances are the same for each battery and you don't need to worry about imbalance after starting. ...............Mike
Mike Moore

Paul, Mike,

Granted my 28 years of Navy electronics was over 20 year ago but the two feet of wire coupling the batteries together is going to have negligible voltage drop...definitely not enough to make any difference. The voltage drop in the wire from the battery to the starter switch (and through the switch) is at least 10 times that.

http://www.calculator.net/voltage-drop-calculator.html
Gene Gillam

Interesting calculator Gene,
I dont have your background in electronics and so i am no expert.

When I first saw this thread, I recalled seeing those 2 diagrams in a caravan magazine article which was discussing a solution to longevity problems some owners were having with batteries connected in parallel and I thought I would pass them on.

The first diagram however, does appear to absolutely equalise the battery connections to both batteries from the starter and the charging circuit and that cant be a bad thing.

I have also moved the connections from my trickle charger to the same positions to make sure it too is charging both batteries equally.

Colyn
Colyn Firth

Colyn,

Although I say it doesn't make any difference there's no reason not to do it the way you described...six of one, half a dozen of another.

Gene
Gene Gillam

I would agree the difference between the two method is minimal because of the very short length of the connecting cables. On the other hand it is wrong to say they are the same. The problem with charging comes because we aren't even talking about a low12 volts but the 1 or 2 volt differential that drives charging hence it is very sensitive to any increase in resistance and all cable has resistance. I was amazed how sensitive 12 volts is to cable resistance when I was trying to get a caravan battery to charge, but distance were over 10 feet not around 1 foot as here.

I wouldn't rush to change whichever system you have.

Paul
Paul Dean

I think the extra cable resistance (nearly one metre extra) could be more like 40-50% of the total (close to two metres) than 10%. Plus, in my circuit at least, the cable resistance is the second largest contributor to circuit resistance after the motor itself (ignoring internal battery resistance).

However, as the negative take off is on the LHS of the battery compartment (as you look at it) and the original positive earth connection connection is on the right then, if you have identical batteries, you really have to go out of your way ,and use more cable, to connect the batteries as in Colyn's second diagram..................Mike
Mike Moore

For charging current of 20 amps over 2-feet of cable, the volt drop is about 0.01 to 0.02 volts, depending on cable size (in the 4-ga to 1-ga size range).

For cranking current of 200 amps, multiply by 10, and you have 0.1 to 0.2 volts on the same 2-feet of cable for a short period of time. That's not going to kill the batteries.

When you switch off (or even when it's running), a battery with slightly higher voltage will drain into the battery with lower voltage, and they will equalize the charge no problem. It will not matter where you connect the cables as the two diagrams above.

The greater problem with parallel batteries is if one would develop an internal short it would pull extremely high current from the other battery, creating an explosive situation. Think melted cables, possible explosion of the battery, boiling battery acid, all bad, not a good prospect. Parallel batteries want high current fuses for safety.
barneymg

Barney. In my parallel batteries set up (see attached photo) would you be inclined for the sake of safety to insert mega fuses (500 amp?) in the mid-point of each of the black battery cables? Tim

TJ Prime

Thank you, Barney.
Gene Gillam

TJ -- One 500-Amp fuse in the hot cable between the batteries. Do not let the cables drag on the propshaft.
barneymg

This thread was discussed between 11/09/2017 and 27/09/2017

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