Improving BMC engine charging

[Poppin]

We have had our Honda EU20i generator nicked and rather than replace it I'd like to get the engine charging up to scratch...

 

We have a 550AH leisure bank, typically we would charge this with the generator via a 60A sterling pro charge ultra. Current engine charging setup has a BMC 1.8 and a single 75A alternator, which is currently putting out max 29A at the start of charge (with the bank at about 65%). This soon drops to 5-15A, long before the bank is at even 80%. As you can imagine, this all makes for slow charging. 

 

1. Does it sound like my belt is loose? I would expect to get higher output from the alternator.

 

2. What are my options in terms of alternator upgrade? I'm sick of messing about with split charing so maybe I can take the opportunity to fit a second, higher output alternator exclusively for the leisures? I'm not hugely bothered about the engine's propulsion power being a bit affected. What is the highest output alternator one could fit to a BMC 1.8?

 

3. I know there are alternator to battery chargers that can increase the amps being put out, any experience with these?

 

3. Or maybe I should be looking at reducing my battery bank? We don't really consume much these days and charing is perhaps too much of a burden.

 

Any advice you can offer is hugely appreciated!

[Robbo]

1, cooling is important, normal alternators are not designed for putting out the amps for long periods.

2, I would look at 120-170amp alternator

3, Not worth the money on a low amp alternator - they work by increasing the voltage on older alternators.   It will also make your alternator work harder (if your alternator doesn't have a decent voltage output already), but your alternator already struggles putting out the amps anyhow!

3!, A large bank or small bank you still have to put in what you took out and with a larger alternator a large bank will be able to take more amps in the bulk stage.

 

 

If you use little you may be already charging okay as the symptons above where the amps drop down to 5amps sounds like your batteries are nearly full, where are you getting the 80% from - that's probably the thing thats off.

Edited November 21, 2018 by Robbo

[Alan de Enfield]

10 minutes ago, Poppin said:

Any advice you can offer is hugely appreciated!

I don't think your alternator is 'far out'.

 

The key thing to remember is that the alternator output is only the quoted figure at something like 6000 RPM.

Assuming you have the 'normal' 3:1 pulley ratios then if your engine is running at 1000 RPM, the alternator is only running at 3000 RPM and its output will be a fair bit lower than its 'rated output'.

 

Secondly - however big your alternator, it is the battery that determines the  current it will take and the last 10%+ takes many, many hours, which is where the solar panels offer benefit (Charge your batteries via the Engine / Generator / Battery Charger in the morning and get the 'bulk' back into the batteries and then allow the Solar to 'trickle' the rest in for the remaining hours of the day) If you had a 150A alternator it would shorten the bulk stage, but would very quickly drop down to 50a - 30a - 15a - 5a exactly the same as your current alternator.

 

Thirdly - how do you know what the capacity is of your batteries ?

 

Fourthly - what voltages (at different stages) is your alternator putting out ?

[canalpubs]

I use a Adverc on a 55amp alternator charging 3 x 110 amp batteries

 

They charge faster and use more of the capacity of the battery

 

Not overly expensive and easy to fit

[alan_fincher]

You don't state the pulley ratio on your current set-up, I think.

That will determine how fast the alternator is being spun, so if as suggested in one post the ratio is 3:1, and you run your engine at 1,000 RPM, then the alternator is spinning at 3,000 RPM.

Even at 3,000 RPM the alternator will not be doing as well as it might be if it were being spun faster, but if your pulley ratio is under 3:1, (as some certainly are on those engines), you will do worse again.

 

Slapping on a bigger alternator, but not spinning it any faster, might produce less benefit than changing pulleys, (if possible) so the alternator is spun faster.

 

My understanding is that trying to run anything of much above 90 to 100A maximum output on a standard single V belt will potentially be a problem, so if you are looking at a thumping great alternator, you may well have to change how it gets driven anyway.

As has been said reducing the size of your battery bank will not help matters if your electricity consumption remains the same.

[MtB]

31 minutes ago, Poppin said:

a single 75A alternator, which is currently putting out max 29A at the start of charge (with the bank at about 65%). This soon drops to 5-15A, long before the bank is at even 80%. As you can imagine, this all makes for slow charging. 

 

I had this a few years ago on one of the boats. Without knowing your voltages at which you get 29A its hard for anyone to comment but this is the first step in finding out why your alternator is not delivering anything like rated output into flat batteries.

 

With the help of the forum I traced the problem on mine to a series of not perfect electrical connections. I was losing (IIRC) best part of a volt between the output of the alternator and the battery terminals. There were several joints I found with 02 or 0.3v dropping across them and once fixed, I got almost full rated output current from the alternator. 

 

And to contradict Alan above, none of my alternators need to spin and anything like 6,000rpm to produce rated output. In fact my 24v 30A Leece Neville pokes out nearly 40A into low batteries with the Kelvin running at 300rpm, 10:1 pulley ratio approx, so 3,000rpm.

 

 

[Boater Sam]

Special crank pulley for poly vee belt over 100A alternator, not easy on BMC 1.8 as the woodruff key is a weak point. 

Get the wiring sorted, buy a 90A Leece Neville alternator, £150, and a Sterling or Adverc alternator controller, run engine at 1200 to 1500 rpm and you will be fine.

[Alan de Enfield]

20 minutes ago, Mike the Boilerman said:

And to contradict Alan above, none of my alternators need to spin and anything like 6,000rpm to produce rated output. In fact my 24v 30A Leece Neville pokes out nearly 40A into low batteries with the Kelvin running at 300rpm, 10:1 pulley ratio approx, so 3,000rpm.

Agreed - but your set up is not the same with a slow 'thumper' driving a 'specialist' alternator with a 'huge' pulley ratio..

A BMC with a generic A127 type alternator, and a pulley ratio of (probably) 3:1 at best is a very different 'apple' (to apple comparison)

25 minutes ago, Mike the Boilerman said:

Without knowing your voltages at which you get 29A its hard for anyone to comment but this is the first step in finding out why your alternator is not delivering anything like rated output into flat batteries.

His batteries are not particularly flat - he says he is getting 29a with the batteries at 65% SoC

[alan_fincher]

21 minutes ago, Mike the Boilerman said:

And to contradict Alan above, none of my alternators need to spin and anything like 6,000rpm to produce rated output. In fact my 24v 30A Leece Neville pokes out nearly 40A into low batteries with the Kelvin running at 300rpm, 10:1 pulley ratio approx, so 3,000rpm.

 

 

Which Alan?

 

The other Alan said......

Quote

Assuming you have the 'normal' 3:1 pulley ratios then if your engine is running at 1000 RPM, the alternator is only running at 3000 RPM and its output will be a fair bit lower than its 'rated output'.

and I said.....
 

Quote

Even at 3,000 RPM the alternator will not be doing as well as it might be if it were being spun faster,

Neither of us has suggested you need to spin at anything like 6,000 RPM, nor tried to quantify how reduced the output would be at half that speed.

Like you I can get a good rate of charge at about 3,000 RPM, but there is no doubt that all the performance graphs for these devices make it plain that at those revs it will be less than if spun faster.

 

 

[cereal tiller]

8 minutes ago, Alan de Enfield said:

Agreed - but your set up is not the same with a slow 'thumper' driving a 'specialist' alternator with a 'huge' pulley ratio..

A BMC with a generic A127 type alternator, and a pulley ratio of (probably) 3:1 at best is a very different 'apple' (to apple comparison)

His batteries are not particularly flat - he says he is getting 29a with the batteries at 65% SoC

A127 Type Alts.Will get hot under full output conditions ,the 6000 RPM quoted speed is for Maximum cooling effect from the Fan ,they will give full output at lower RPM but the Regulator will reduce output to prevent overheating.

[MtB]

21 minutes ago, alan_fincher said:

Which Alan?

 

The other Alan said......

 

Alan De E.

 

He also said:

 

1 hour ago, Alan de Enfield said:

The key thing to remember is that the alternator output is only the quoted figure at something like 6000 RPM.

 

Which is the bit I was saying to the OP is not necessarily true in my experience with my alternators.

 

 

27 minutes ago, Alan de Enfield said:

Agreed - but your set up is not the same with a slow 'thumper' driving a 'specialist' alternator with a 'huge' pulley ratio..

A BMC with a generic A127 type alternator, and a pulley ratio of (probably) 3:1 at best is a very different 'apple' (to apple comparison)

 

Again I disagree. My alternator with the low output was a cheap A127 clone from the car accessory shop.  

 

I also hold that the alternator neither knows nor cares whether the engine driving it is a 'thumper', or not, provided it is being spun at about 3,000rpm or so. 

[alan_fincher]

7 minutes ago, Mike the Boilerman said:

I also hold that the alternator neither knows nor cares whether the engine driving it is a 'thumper', or not, provided it is being spun at about 3,000rpm or so. 

How are you measuring your 3,000 RPM alternator speed?

A tacho actually on the alternator, or by measuring engine RPM and then calculating based on pulley ratio?

If the latter, I was surprised how inaccurate trying to estimate the actual pulley ratio can be, (having measured both engine RPM and alternator RPM using the same tacho).

[MtB]

16 minutes ago, alan_fincher said:

How are you measuring your 3,000 RPM alternator speed?

A tacho actually on the alternator, or by measuring engine RPM and then calculating based on pulley ratio?

If the latter, I was surprised how inaccurate trying to estimate the actual pulley ratio can be, (having measured both engine RPM and alternator RPM using the same tacho).

 

Pulley ratio. 

 

Go on then, surprise me too! How inaccurate was your speed estimate using pulley ratio compared to the hand held tacho?

[Alan de Enfield]

25 minutes ago, Mike the Boilerman said:

Again I disagree. My alternator with the low output was a cheap A127 clone from the car accessory shop.  

When did you mention your A127 clone. The only reference I can find to you mentioning an alternator is :

 

1 hour ago, Mike the Boilerman said:

In fact my 24v 30A Leece Neville pokes out nearly 40A into low batteries with the Kelvin running at 300rpm, 10:1 pulley ratio approx, so 3,000rpm.

A 24v Leece Neville is not what you would expect to find attached to a BMC 1.8

[Poppin]

Thanks for all the replies in such a short timeframe!

 

I have been on the phone with Adverc and they've sent me over some documentation. Seems they do a reasonable discount if you purchase both a 90A alternator and Adverc controller. Just trying to absorb all the info in what they've sent. 

 

To quickly answer some of your questions: 

 

I base the SOC on the Smart bank advance system I have installed. 

 

Hopefully this picture will give you an idea of pulley ratio (I KNOW THE POWDER RESIDUE IS FROM THE BELT, this is an old pic)

Edited November 21, 2018 by Poppin

[philjw]

How would you calculate the pully ratio when the water pump is also driven by the crankshaft pully? Is it simply ignored?

[MtB]

2 minutes ago, Alan de Enfield said:

When did you mention your A127 clone. The only reference I can find to you mentioning an alternator is :

 

A 24v Leece Neville is not what you would expect to find attached to a BMC 1.8

 

The 127 clone was the alternator with the high resistance wiring. I went on to quibble your implication that 6000 rpm was required for full alternator output using a different boat and different alternator as an example. It was your incorrect assumption at play here! 

[Alan de Enfield]

3 minutes ago, Poppin said:

I base the SOC on the Smart bank advance system I have installed. 

Isn't the Smart Bank just a split charge system and is / can be used in conjunction with a Smart Gauge ?

 

Have I misunderstood ?

[Poppin]

1 minute ago, Alan de Enfield said:

Isn't the Smart Bank just a split charge system and is / can be used in conjunction with a Smart Gauge ?

 

Have I misunderstood ?

Smart bank advance is installed with smart gauge

[Robbo]

3 minutes ago, Poppin said:

I base the SOC on the Smart bank advance system I have installed. 

I would do a manual confirmation to confirm SOC, once the charging amps have reached below 3-5.    

[Alan de Enfield]

Just now, Poppin said:

Smart bank advance is installed with smart gauge

Thank you.

[MtB]

4 minutes ago, philjw said:

How would you calculate the pully ratio when the water pump is also driven by the crankshaft pully? Is it simply ignored?

 

Yes. 

 

[Alan de Enfield]

1 minute ago, Robbo said:

I would do a manual confirmation to confirm SOC, once the charging amps have reached below 3-5.    

Good advice, (particularly where Smart gauges are involved).

[philjw]

1 minute ago, Mike the Boilerman said:

 

Yes. 

 

Thanks Mike. In that case the ratio of the OP pullys does look around 3:1 to me.

[bizzard]

12 minutes ago, philjw said:

How would you calculate the pully ratio when the water pump is also driven by the crankshaft pully? Is it simply ignored?

It'll make no difference to the ratio.