bmc 1500 alternator / power upgrade

[dccruiser]

I have a 1500 bmc in my n/b with a standard alternator and want to upgrade it, i believe it to be a 40 amp unit, what i propose is to either add another alternator as i have seen some with a twin alternator setup , or just upgrade the existing one to a 70+ amp unit.

I have a 90amp alternator to battery charger and 4 x 110 amp leisure batteries, so i would either fit a 70 to 90 amp alternator as a secondary unit if i can source the appropriate mounting bracket ... or anyone out there has one on a u/s lump, or upgrade my current alternator.

I am currently on shore power with a sterling 20 amp charger, but intending to be long term cruising from spring.

Main power requirements are an 1800watt sterling inverter to power a microwave and hair dryer etc. and a 12 volt engel fridge. I will also be using all the other usual things such as a lcd tv, sat box, laptop etc.

 

Rick

Edited November 15, 2010 by dccruiser

[Evo]

I bought one of these 70amps http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=400145459063

 

I have a double alternator setup though and this is a spare for my engine battery charging only. I have a 110amp on my cabin batteries.

 

If you stick with just one alternator I dont see a problem if your cruising everyday. I reckon our engine alternator does sod all most of the time anyway.

 

I got that particular one because it has a W for rev counter which I dont have at the moment but want to fit at some time.

[RobinJ]

I have a 1500 bmc in my n/b with a standard alternator and want to upgrade it, i believe it to be a 40 amp unit, what i propose is to either add another alternator as i have seen some with a twin alternator setup , or just upgrade the existing one to a 70+ amp unit.

I have a 90amp alternator to battery charger and 4 x 110 amp leisure batteries, so i would either fit a 70 to 90 amp alternator as a secondary unit if i can source the appropriate mounting bracket ... or anyone out there has one on a u/s lump, or upgrade my current alternator.

I am currently on shore power with a sterling 20 amp charger, but intending to be long term cruising from spring.

Main power requirements are an 1800watt sterling inverter to power a microwave and hair dryer etc. and a 12 volt engel fridge. I will also be using all the other usual things such as a lcd tv, sat box, laptop etc.

Each alternator will take about 200 rpm of your engine speed, but more importantly, the alternator needs to rotate sufficiently fast, so pulleys and belts are important, 4 to 1 ratio probably required. When you do move you may find a lack of power and reduced speed (depending on prop. size of boat etc.), may even develop black smoke!

[alan_fincher]

It seems to be generally accepted that about 70 amps is the largest alternator that can reasonably be driven off a standard BMC pulley and single V-belt with no likely issues.

 

Some seem to push this to 90 or 100 amps, but it is usually recommended to change the pulleys and drive belts to something more substantial than the standard automotive item, once you go much above a single 70 amp alternator.

 

If you are to get any reasonable charge at tick-over, you probably need a pulley ratio of at least 3 to 1, but obviously the higher you go, the more load it will place upon the engine at any given engine RPM. 4 to 1 might be [pushing it with a big alternator on a 1500, I'd have thought....

[David Schweizer]

I have a 1500 bmc in my n/b with a standard alternator and want to upgrade it, i believe it to be a 40 amp unit, what i propose is to either add another alternator as i have seen some with a twin alternator setup , or just upgrade the existing one to a 70+ amp unit.

I have a 90amp alternator to battery charger and 4 x 110 amp leisure batteries, so i would either fit a 70 to 90 amp alternator as a secondary unit if i can source the appropriate mounting bracket ... or anyone out there has one on a u/s lump, or upgrade my current alternator.

I am currently on shore power with a sterling 20 amp charger, but intending to be long term cruising from spring.

Main power requirements are an 1800watt sterling inverter to power a microwave and hair dryer etc. and a 12 volt engel fridge. I will also be using all the other usual things such as a lcd tv, sat box, laptop etc.

 

Rick

We have a BMC 1.5 engine in our boat, and I cannot see any way in which a second alternator could be fitted, there are no location points on the other side of the engine, and the Fuel injector pump is also in the way. Fitting a second alternator above the existing one would foul the No. Injector, so I think that proposal is a non starter.

 

The only realistic option is to fit a higher output alternator, particularli if the unit fitted to your engine is the "standard" 35amp model. Fortunately the Lucas A127 alternator which is readily available in outputs up to 70amp (possibly higher) will fit the BMC 1.5 lugs without any modification, except perhaps a couple of slim packing washers. Re-built models can be purchased from a range of suppliers, I get mine from these people:- Vehicle Electrics (Birmingham) Ltd. 166 Stockfield Road, Acocks Green, Birmingham, West Midlands, B27 6AU. Tel: 0121 7060688

 

As already suggested by Alan Fincher, a higher output alternator can cause belt slipping under load, and you will almos certainly need to alter the pulley set up, by having the pulleys machined out from the standard 9mm to 13mm wide and fitting a smaller alternator pulley. Most Marinised BMC 1.5 engines have quite a large drive pulley (about 9 1/2" from memory) with something like a 3" pulley on the alternator. If the drive pulley is smaller it would be worth considering fitting a larger one together with a smaller alternator pulley, to bring the ratio closer to 4:1. This will certainly allow you to get maximum output a slower engine revs.

 

I fitted a 55amp A127 alternator to our BMC 1.5 and soon found that there could be significant belt slippage under maximum load with the standard 9mm belt. After having the pulleys machined out, the problem disapeared. The wider belt is readily available - size 1050 x 13 . I get mine from Halfords model No. HB1050c.

 

I note that you are based in Shardlow so there could be someone lcocally who can help you out, if not, I can recommend a good engineer in Braunston. PM if you require details.

 

I hope this helps.

Edited November 15, 2010 by David Schweizer

[Evo]

David, Theres loads of 1.5's and 1.8's with 2 alternators, not only that ours has an additional small pulley on the crankshaft (making a total of 3 pulleys) for the Jabsco raw water pump aswell.

 

Our 2nd alternator is on the same side as the std one and has its own special casting for a mounting (not an afterthought fabrication). Even the Jabsco pump is mounted on its own specially made adjustable casting on the other side of the engine.

 

Our engine was originally Thorneycroft, and I assume these mods were done properly by them and utilise their own fabricated engine mounting brackets.

 

As to belt slip, I have experienced it when the belts are slack or when the wrong section belt has been fitted, otherwise no problem at all.You can just about see everything in this pic.

 

I have seen the same on a 1.5.

 

Edited November 15, 2010 by Evo

[RobinJ]

We have a BMC 1.5 engine in our boat, and I cannot see any way in which a second alternator could be fitted, there are no location points on the other side of the engine, and the Fuel injector pump is also in the way. Fitting a second alternator above the existing one would foul the No. Injector, so I think that proposal is a non starter.

Many mounting brackets were fitted with a alternator mountung tube so one could be bolted on the lift pump side low down. There are also double pulleys available to replace the standard crankshaft pulley to drive them!

[David Schweizer]

David, Theres loads of 1.5's and 1.8's with 2 alternators, not only that ours has an additional small pulley on the crankshaft (making a total of 3 pulleys) for the Jabsco raw water pump aswell.

 

Our 2nd alternator is on the same side as the std one and has its own special casting for a mounting (not an afterthought fabrication). Even the Jabsco pump is mounted on its own specially made adjustable casting on the other side of the engine.

 

Our engine was originally Thorneycroft, and I assume these mods were done properly by them and utilise their own fabricated engine mounting brackets.

 

As to belt slip, I have experienced it when the belts are slack or when the wrong section belt has been fitted, otherwise no problem at all.You can just about see everything in this pic.

 

I have seen the same on a 1.5.

 

 

I stand corrected. If I had not seen that photo, I would not have believed it possible, but it clearly is.

 

It is fairly clear from the photo that neither alternator uses the manufacturer's original mounting lugs as designed, and that some fairly large auxilliary brackets are being utilized to enable two alternators to be used. Certainly the arrangemet illustated would not fit inside the engine box on our boat, which is designed to give about two inches clearance of the standard engine at the front and sides.

[ditchcrawler]

I have a 1500 bmc in my n/b with a standard alternator and want to upgrade it, i believe it to be a 40 amp unit, what i propose is to either add another alternator as i have seen some with a twin alternator setup , or just upgrade the existing one to a 70+ amp unit.

 

This came up about a month ago from someone else.

When I passed Calcutt Marina I enquired about fitting a second alternator for him and they told me that there is not a standard bracket available for the 1500 BMC engine, but they could fabricate something if so required.

[dccruiser]

Thanks for all the information chaps, i will no doubt end up settling for the 70 amp A127 route , unless as i said i can find a duff engine with a 2nd alternator setup on that i can rob the parts off.... as i have until spring i may just get lucky yet! i saw one on fleabay recently selling for spares or repair, it was sat at just over £100, i bid 160 and was trounced at the last second... that would have been ideal as i would have had 2 alternators, plus double pulley and bracketry then sold what was left over.

 

I honestly thought there would be a good chance someone would have one as i have come across several bmc 1500's over the years with a second alternator, most mounted under the lift pump.

 

I know if i am cruising virtually every day i can cover my power requirements, but i do want to be able to stop a few days here and there without depleting my batteries too much, or having to think about how many times i open my fridge everyday or even be switching it off at night. i should have also added my eberspacher d5w based central heating to my power requirements.

 

Rick

[Slim]

I have a BMC 1.8 fitted with two 70amp alternators. The general configuration is very similar to Evo's. The engine came out of a Telecom Sherpa van and has a twin belt crankshaft pulley. (I've always assumed this was to accommodate power steering.) The second alternator is fixed to the front offside engine mounting bracket. If I recall correctly I sourced this from AMC in Manchester about 10 years ago. They may still be able to help.

 

 

Frank

[dccruiser]

I have a BMC 1.8 fitted with two 70amp alternators. The general configuration is very similar to Evo's. The engine came out of a Telecom Sherpa van and has a twin belt crankshaft pulley. (I've always assumed this was to accommodate power steering.) The second alternator is fixed to the front offside engine mounting bracket. If I recall correctly I sourced this from AMC in Manchester about 10 years ago. They may still be able to help.

 

 

Frank

 

Hi Frank,

Thanks for the info, could you tell me what the AMC stands for or give me any more info as i could not find them on the web.

cheers

Rick

[Theo]

But obviously the higher you go, the more load it will place upon the engine at any given engine RPM. 4 to 1 might be [pushing it with a big alternator on a 1500, I'd have thought....

 

Assuming that the alternator runs sufficiently fast to generate the maximum regulated current then higher speed means less torque required to turn the alternator:

 

Power = torque x angular velocity

 

Power is constant (say 14V x 70A)

 

Therefore a higher angular velocity (revs) must result in a lower torque.

 

Nick

[alan_fincher]

Assuming that the alternator runs sufficiently fast to generate the maximum regulated current then higher speed means less torque required to turn the alternator:

My point was not intended to be about generating the maximum current the alternator can produce.

 

It was meant to be about the load that the alternator will attempt to place on the engine when it is running at low revs, and specifically at tick-over.

 

In that instance say trying to drive the alternator 4 times faster than the engine will attempt to generate a higher current, and hence place a greater load on the engine than (say) pulleying up at 3 to 1.

 

I don't think the average BMC 1.4 would be comfortable at (normal) tick-over with a bloody graet alternator that you are trying to drive with a 4:1 ratio on the pulleys. I think it will be trying to load it up too much.

 

I could be wrong, but I suspect I'm not....

[Slim]

Hi Frank,

Thanks for the info, could you tell me what the AMC stands for or give me any more info as i could not find them on the web.

cheers

Rick

[nb Innisfree]

My point was not intended to be about generating the maximum current the alternator can produce.

 

It was meant to be about the load that the alternator will attempt to place on the engine when it is running at low revs, and specifically at tick-over.

 

In that instance say trying to drive the alternator 4 times faster than the engine will attempt to generate a higher current, and hence place a greater load on the engine than (say) pulleying up at 3 to 1.

 

I don't think the average BMC 1.4 would be comfortable at (normal) tick-over with a bloody graet alternator that you are trying to drive with a 4:1 ratio on the pulleys. I think it will be trying to load it up too much.

 

I could be wrong, but I suspect I'm not....

 

Agreed, we have a large frame 24v 100a Leece Neville on a 2:1 ratio running from a LPWS4, This loads the engine just about right and gives a good compromise, any higher ratio would def start to overload.

[Slim]

Hi Frank,

Thanks for the info, could you tell me what the AMC stands for or give me any more info as i could not find them on the web.

cheers

Rick

 

 

Rick,

 

Sorry about previous blank post, I pressed the wrong key!

 

When I last had dealings with them their name was AMC Diesel Engineering. Try www.amcdiesel.co.uk It opens as Thornycroft and they are who I meant. I've looked through all my old invoices but can't find the one with the bracket on it. I suspect I'd given up keeping them by then. Whilst I'm sure they were the people I got the bracket from if they can't help get back to me and I will let you know the other suppliers I dealt with.

 

Good luck,

 

Frank