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MG MGB Technical - Twin 6v to single 12v under bonnet?


Has anyone ditched the twin 6v batteries in the battery boxes and gone to a single 12v battery located under the bonnet?

Is it a simple matter of re-routing the cable from the battery? Any gotchas? What spec battery did you use and how did you mount the battery under the bonnet?

I am interested in doing this as I will be road rallying my MGB and so at some point will have fixed back seats, a half roll cage and maybe hard top. In which case it will be hard to access the 6v batteries if I need to.

Thanks,
Jamie
jamieo

I've seen it done with a battery box mounted on the flat where the washer fluid bottle is normally positioned (charcoal canister on later, American models). In your case, that would be on the right side, above the passenger's feet.

I don't think that there is any particular problem. Just re-route and shorten the cable and mount a new ground cable.

However, it might be better to use a single 12v battery in the right side original battery bin. This would maintain the front/rear weight distribution better. On LHD cars, this give a little better side-to-side weight distribution, as well. On a RHD car, a longer cable would allow you to put the battery in the left side bin, to accomplish the same thing.

Do you really need to access the battery during a rally?
Paul Noble

fixed back seats? for a road rally car? I don't understand.
Wade Keene

Probably should have read "fixed seatbacks".
George B.

Jamie,

I've converted to a single 12v, but it is located in the existing left hand battery bay. The trick is to get one the right size. I like the idea of moving it forward but having had to remove them from a midget, which locates them dead center immediately in front of the firewall, they are a pain to remove without wrecking your back. Not sure where you'd put it in the front of the B.

I plan to install a battery switch in the engine compartment to be able to disconnect it for servicing without having to get in behind the seats.

Mike
Mike

The previous owner fabricated a stainless steel case, and mounted it to the top of the right front fender well. The bolts go down though the fender well, right near the shocks. It works well, easy removal for winter, the only problem I see is that it necessitated rerouting of the oil cooler lines, to under the box. I also added one of those yellow acid neutralizing pads, in case it should ever leak. This arrangement has a 1 foot ground to the top of the head, and about a 2 foot positive cable to the starter. Easy to jump should I ever need it.
Joe

Hello Jamie,

hereīs the link to such a conversion:

http://www.mgcars.org.uk/pics/neuhaus3.jpg
joern


By fixed back seat I meant "fixed-back seat", i.e. the back won't recline or fold forwards, specifically I'm thinking of a modern style bucket seat. Along with a rear roll hoop and a hard top this would mean getting to the battery boxes would be difficult, hence the desire to put the battery up front. Access to the battery is desirable for scrutineering or to quickly fix things/replace it.

I know this is possible, as shown above, and there is plenty room around where the washer bottle is located. Here's a picture of my car:

http://popdog.dyndns.org/interests/cars/pictures/mgb_lives/Picture%20002.html

So the battery could be located in the top right, where the washer bottle is and the washer bottle moved to between the heater box and the battery.

What I really wanted to know is how do people actually mount the battery in such a location? The area is a flat plate, but what do you seat the battery on? Something fabricated just for this or some kind of off the shelf part? How do you then bolt the battery down?

Also what kind of spec 12v battery is required at minimum (so I know to maybe get a stronger one)?

If anyone's interested, here are some other pics of the car:
http://popdog.dyndns.org/interests/cars/pictures/mgb_lives/index.html

Cheers,
Jamie
jamieo


Ah found this link that help with some:

http://www.mgcars.org.uk/MG_Elec-Tech/conversion.html

But doesn't address the how to mount in the engine bay parts.

Jamie
jamieo

There are a few captive nuts already fitted, as the same body could be used for left or right hand drive, then the pedal box etc, would need to be fitted on either side.
Tatty

I don't see the advantage of mounting such a heavy objec as a battery higher, and in the front of the car.

I always assumed that the batterie(S) were mounted low and behind the seats to improve weight distribution, and lower centre of gravity slightly.

I've fitted a 12v battery in the nearside box , and boxed in the offside box, and put a lid on it , and it now carries my pump, first aid kit, fire extinguisher and a few tools.

When I re-reouted the cable I also fitted a removable switch just behind the seat, which effectively isolates the battery when I leave the car.

Mike
Michael barnfather

Jamieo, MG was smart putting it where it did. It's low, centered, and does a lot for vehicle balance. What I would do if I were you is look at Triumph GT6s. I don't know about later ones, but early ones used fixed-back seats on a mechanism that allowed the entire seat to be tilted forward for access to the back. Pretty nifty, and it should be easy to convert for the B. That was my plan.
Alternately, go find an 80s 3-series BMW. They put the battery in the trunk, but under the hood is a nifty terminal thing to allow jump starting or whatever. Would be easy and cheap to snag and mount someplace accesible. Then you just route your cables to it. Very clean, and you keep the benefits of NOT having the battery high and forward.
Baxter

A roll bar won't bolt or weld in so it's blocking access to the battery. If it did, it would be bolted or welded to the battery access panel and that's not how its done. As far as the hard top and seats go, I really think your just looking at making something thats a bit of a PIA into just a little bit more of a PIA. As far as fixing things and replacing, etc., back there, a battery should last for years and there are three connections back there to worry about. Assuming you do things right, they won't need much attention. Scrutineering-wise, the inspector has to make sure the battery is securely held down. If they have to contort themselves a bit more than if you had a car with the top down and seats folded forward, will they not check your car? It just seems to me that you are looking to make more work for yourself (and building a rally car is plenty already) that could have some detriment to handling, which should be more important in a rally car than a normal one, for a dubious benefit. If you check out the trunk mount, think about a way to vent battery gases out of there so nothing blows up.
Wade

As far as sizing the battery, there should be nothing in a rally car requiring a battery with more CCA's than a street machine unless you park with the engine off and do navigational plots.
George B.

Jamie,
IMHO its a very good idea to fit the battery in the engine bay.
That talk about weight distribution is not relevant because you wonīt notice a different road holding with 5 kg plus or minus at the front or rear.
But what you will notive is how easy it is to service the battery in the front: takes 10 secs to fit jump leads, 1 minute to take the battery out and it never again gets dirty and forgotten. And: the car starts better because the main power supply from the battery to the starter motor only has a length of about 60 cm instead of 3 metres. (longer on a lhd car)
I enjoy this setup for more than 20 years in my car.
Take a battery from a VW Golf or a 3-series BMW, they fit and you can even fix them to the floor without drilling a hole or fabricating a fixture: use one of the bolt holes (with captive nut) that are present an this panel.
joern

Joern, I respectfully disagree. If you drive hard and are in tune with the car, you'll notice a difference. In a race or rally situation, you'll definitely be paying a penalty. It's in a good spot as is. I do, however, think using the terminal box from an E30 BMW is a good compromise, as I mentioned above, as it would allow access to the circuit for jump starting or whatever. As far as ease of battery maintenance goes, I think that's the real non issue. A decent modern battery should be fine, even completely ignored for at least 3 years or more. And that's under extreme conditions, like Arizona desert heat. A good Optima cell should be fine for even longer.

In a race car, the goal is to get the weight as evenly balanced and low as possible. The batteries already as low as it can go in a B. A single 12v opposite the driver helps balance his weight and provides about the best balance compromise he can find.

A battery high and on the front is going to promote understeer, which is bad in general and unforgivable on a rally car.
Baxter

Baxter,
I didnīt notice a difference in the last 20 years - nor did a couple of knowledgable friends who drove my car and compared it to theirs.
And your point with the rallye car is understood but here I disagree :-))
thereīs a rollcage, the spare wheel in the boot, maybe a bigger tank, rear axle mods (maybe a panhard rod) and many more things that all add weight to the rear of the car. On the other of the car you usually save weight under the bonnet with a freeflow manifold for example (instead of the heavy cast item).
In the end you will not change the balance by a noticable margin by just changing the battery location.
But maybe you are just driving so much harder than me and any mg-owner I got to know since 1978 (when I bought my car) :-))))
Or maybe the antitramp bars fitted to my banjo axle make up for the loss of the battery-weight in the rear :-))))
joern

Joern, you do make a good case. I still think it's may more effort than it could possibly be worth, and even with the added weight involved in a rally car, the last thing I think you want to do is move more weight above the car's roll center, but hey, it's a big world, and my way ain't the only way. I've always thought putting the batteries were they did was one of the B's more clever ideas.
Baxter


I shall probably be keeping the batteries behind the seats and going to a single, modern, 12v battery at some point. I've discussed this with someone with experience rallying and he said that he's never had his battery/earthing scruitineered and a modern battery is so reliable you don't need to worry about it. On top of that, I can probably use the under-bonnet space for something more useful.

I don't think the 12v under the bonnet is a bad idea though. The batteries aren't so heavy, and a fully loaded rally car has so many changes that affect weight distribution anyway that it's not like comparing it to a standard car. The raised weight is an issue though, but probably not critical for rallying. I have seen a number of historic race MGBs with the battery located there though.

Other good reasons for moving the battery were - removes the possibility of damaging the underbody cable from the battery (you can do this by routing it inside the cockpit though, as you would do other electric/brake/fuel lines anyway) and it removes the possibility of battery damage from below (which can be rectified by putting skid plates on the bottom of the battery boxes anyway).

Jamie
jamieo

This thread was discussed between 09/12/2002 and 12/12/2002

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