Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Sizing Battery Fuse?

I am flipping the battery in my 67 +4 from behind the driver's side to passenger's.

This requires a longer +ve power cable. So I am going to use a new mega fuse and holder to provide the 8mm junction terminals to hook up a new 'tail' for the short additional length required. This provides a 'twofer' solution of saving me running a new power cable, and introducing a battery power fuse.

Question is, what size fuse do I use? Starting bid is 100A continuous (blows as twice that).

Yes/ No/ Maybe...?

Cheers, Colin

Best to use an entirely new positive battery cable Colin, unfused (starter feeds are rarely fused and you don't want joins in this cable anyway) direct to starter battery connection assuming it's piggy back solenoid type. If it's older pre-engaged type then connect to remote starter solenoid.

Given the short run in either case you can then take a short lesser current cable via an 80 amp fuse if you wish (although I wouldn't bother for such a short run as circuits will be individually fused later) to main 12 volt distribution post and/or alternator output from the same starter or solenoid connection terminal.

Suggest 50mm2 for starter cable and 10mm2 for main distribution.

Hi Colin,

First review RichardV6's post. It is very good, once again.

You are smart to switch the battery side. It is the first thing LHD Morgan owners should do. The MMC does not design for LHDers and some of the results can be anywhere from unwanted to hilarious. Even the ignition switches were installed upside down! (A tale for another day.) The placement of the battery behind the driver is a very basic automobile no-no..exaggerated by the low weight of our cars. (yours was 1848 lbs from the Works almost exactly the same as they made for me in 2002) That makes any weight placement vital and if we double the weight of a standard battery (the effect of moving it from one side to the other..that shifts 5% of the total car weight) changing the handling. It is also the reason, IMHO, that LHDs more often develop the traditional leaf spring sag on the driver's side.

A car battery fuse strength should be calculated as the total draw of the car plus 20-25% . Your earlier Morgans does not draw much..so 80-100 amps should be enough unless you want to count things up and be more precise. Do not put in a more powerful fuse than you need to, that is the recipe for negating the entire reason for fuses and can cause wiring fires.

I would also consider, along with a new battery power cable, a shut-off switch. If you install it through the rear wooden bulkhead it is easy to access. If you mention it to your insurers, there is normally a discount as most will consider it an anti-theft device. However, IIRC, UK auto insurance is not strictly government regulated and terms an coverage vary.

Avoid the MMC shut-off switches. They are plastic and their internals melt. https://www.gomog.com/allmorgan/CarBatterySizes&BatteryCutoffSwitches.html#CUT

Don't fuss about the battery. The only thing important about a battery in good condition, is that is the correct size for its placement, that it can turn the engine and that it can be found any place on a holiday Sunday.

gmg