Alternators and Charging

[alb40]

Goodday all.

I have a bmc 1.5 with a standard lucas type alternator which is about 35 amps. I find that this is simply not powerful enough to give a good charge to my batteries so can anyone recommend another alternator as a direct replacement which is more powerful?

Cheers

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[VicS]

The first question is why is a 35 amp Lucas alternator not powerful enough.

The alternator not working correctly? Is the regulator OK? Is the rectifier OK? Is it turning at the right speed?

Do you have a very large demand for power on board?

Do you have a huge battery bank?



<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>

 

[Jcorstorphine]

I have to agree with vicS as a 35 amp alternator will charge most batteries relatively quickly unless as vicS says, you have installed a gigantic traction battery. Are you running an electric fridge while the engine is running as this will gobble up about 8 amps or so. I used to have a BMC engine and I do not remember the charging current being any higher than about 15 to 20 amps immediately after the engine was started and this dropped quite quickly down to 10 and then down to just a few amps. If you are doing a large number of stop starts then perhaps there is a case for a bigger alternator.

Do you have an ammeter which displays the charging current, if so, start the engine and wait for the ammeter to give a steady ready then switch on every single thing on the boat and watch what the ammeter displays. I have to mention this test will only work if the ammeter is in a part of the wiring circuit which see the charge and the discharge currents. Assuming the ammeter sees the load then it should climb with every device you switch on. A 24 watt bulb will take 2 amps, a 100 watt fridge will take 8 amps and so on. The object being to see what the alternator can output.

As to the alternator, if you go along to your local CAV they will test the unit for you and may be able to give you an upgrade. Halfords will charge you about £75 with a trade in


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[john_morris_uk]

More specifically perhaps a battery audit?

What is your total Ah capacity of your battery bank?

Calculate and measure and add up all the drain that you anticipate between charging. Allowing for some charging losses (perhaps 115% back for whatever you take out of the battery bank) you can then have some idea of your charging requirements. (And bearing in mind that you should try not to discharge most sorts of lead acd batteries - even marine deep cycle ones - down to less than 50% of their capacity.)

You then have some sort of idea of how much charge you need to replace. Unfortunately the physics of batteries then gets in the way.

At first, the plates will accepts a high charge current.
As the bank recharges less and less current actually 'gets through' in a sense to the charging process.

What regulator do you have? Assuming you have a 'smart' regulator that tries to forces as much charge as quckly as possible into the batteries, the next problem is losses. Heat (among other things) degrade your alternator to the point that when it is hot and actually trying to charge, you are lucky to get anything much over 50% of the rated output.

Sadly putting as bigger alternator on may only be part of the picture. Hope that this helps...

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[huldah]

I recently had a similar problem, due to a 0.5 volt drop between the alternator and the battery. Suggest you use an electronic multimeter and measure this. Best done immediately after starting the engine. I have not yet traced the cause as the wiring desperately needs modernising. I made a temporary repair by fitting a heavy duty cable. This leaves the ignition light 0.5 volt below battery voltage, ok for winter charging, but will almost certainly overcharge when cruising.

I was a bit surprised at a replacement Lucus alternator costing £70-00. I bought a replacement from my friendly autoshop for £27-00. I thought it had a similar output.

Philip

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[Talbot]

If the alternator is OK, you would probably be better of adding an alternator regulator in order to be able to use the power it is capable of providing. (Talk to Sterling or Adverc)

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[Gunfleet]

Depends on the size of your batteries. Some sources quote a minimum of 1/3 the Ah of your battery as the rating of the alternator, so your alternator would only comfortably charge 110 Ah . Adverc suggested I went up to 70 amp Lucas for my 220 battery bank, then I added a seperate 80 ah battery for starting. This set up seems easily able to cope, since the starter battery is rarely below full charge. A 32 watt solar cell keeps everything up to snuff between visits.

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[William_H]

Hello huldah You may have the wrong impression re voltage drop between generator and battery. If it is bad wiring this drop will be from resistance (bad connection or thin wiring) As the current to the batteries falls as they become charged (assuming no other load) then the volt drop will reduce ie the voltage to charge the batteries will return to that coming from the generator (as regulated) so batteries should eventually charge fully to generator voltage just more slowly due to the resistance in the wiring. Now if you have a diode (splitter) in the line this will drop .7 volt regardless of current. (different to resistance) and hence the battery won't charge fully and if you bypass the diode with your additional heavy wire the battery will come to a greater charge state (possibly boil over a long period).
alb40 If your battery is not doing it's job it doesn't mean it is not being charged. More likely terminal old age. The only way to ensure the charge system is working is to have an amp meter to indicate how much is going into the battery. A voltmeter can help in as much that if the battery comes up to 13.75 volts then the generator is charging it. The 35 amp rating for the generator is for situations like in a car where at night in the rain you may have 5 amps charging the battery and 30 amps powering headlights wipers heater etc. As you approach the capacity of the generator the voltage will fall so battery charging becomes less. Now in your boat assuming there is no other load the generator (altenator is another name in this context) delivers 13.75 volts and the current then flows into the battery. As the battery charges the current into it must fall. The result is that unless you have a very large battery that is very flat you will only get a large current into the battery for a short period ( like a minute) before current falls dramatically. ( like to 5 amps) The battery charge never reaches full because the closer it gets to full the less current goes in. ( the current into the battery results from the difference between the voltage at the generator and the voltage the battery produces itself) It is however quite adequate and means that the battery is never overcharged even on a long trip. The smart chargers overcome this problem by increasing the charge voltage for a period to increase the charge current to get the battery more fully charged in a short period then reduce the current to a safe level for long term charging. (great if you are running the engine solely to charge the batteries).
It is most likely you have a dud battery or a dud generator but a larger generator may be a waste.
regards will

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[davehu]

The 1.5 BMC engine orginally had a dynamo so the crank pulley was small, when they fitted an alternator they had to fit a much smaller pulley to the alternator, even then the spped of the alternator is reaaly to slow and until you run the engine fast the output is not up to 35 amps. The solution is to fit a lager pulley system to get the alternator up to speed.

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[snowleopard]

don't think a large-capacity alternator will necessarily help. i have 330 AH of batteries and 2 x 55 A alternators, controlled by an adverc. the most input current i ever see is 35A even with both engines running.

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[cliff]

In answer to your question, I believe you can fit an 18ACR directly in place (standard frame size alternator - this should give you 80amps plus on full load.

However before you run out to Lucas to get one (forget Halfords) check the cabling between the alternator and the batteries, Check the earth (negative ) cable where it connects to the engine block, check the voltage at the batteries when the engine is running and slowly rev the engine up until you get max voltage. Alternators are supposed to work at low revs as compared to a dynamo.

Finally measure the dia of the crankshaft pulley, remove the alternator and take it into your local Lucas and ask them to test it, also ask for the max speed allowed for the alternator and work back from the max speed of your engine (3500 rpm?) to give pulley size.

I run a 60 amp via a Sterling regulator to charge ~300ah of batteries and depending on how much punishment SHMO has given the inverter, I can charge the battery bank at the full 60 amp (20A/battery?) initially and for maybe ½ an hour or so after starting the engine. This charge rate is achieved at little more than a tick over.

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[Ships_Cat]

That seems low, with 330 AH of batteries I would have thought that they would accept somewhere between 55 - 65 A (say up to around 0.2 x capacity) at the early stages of charge if deep cycle batteries and maybe higher, perhaps at the level JohnM suggests, if cranking batteries.

As one example, with 520 AHr of batteries we get around 100 A to start with (around 0.2 x capacity), dropping fairly quickly to around 95 A as the charge builds up on the plate surface (that being my assumption).

Maybe it is a characteristic of your batteries but if not I wouldn't have a clue what the reason was.

John
<hr width=100% size=1>I am the cat but I am only 6.

 

[macd]

Have you tried AMC Thonrycroft, who I believe now have the rights to these BMC engines? They can supply a 70A alternator off the shelf, and can no doubt advise on pulley ratios etc. I've found them very helpful in the past.

Tel: 01772 613003
www.thornycroftengines.co.uk

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[pappaecho]

Agree with Davehu, older engines like BMC and Perkins used dynamos, which had to revolve quite slowly due to the physical weight of the armiture. First generation alternators, really did not spin fast enough at lower revs to give adequate charging at the relatively low revs of a diesel engine. My brothers Watermota has a Bosch alternator fitted, and the engine has to be blipped to about 3000 revs to get the alternator to cut in, thereafter it is fine, and charges quite happily at 1500 rpm - but it is 55 amp. My Perkins 4108, again has a 45 amp alternator, but a very small pulley which means it spins at much higher revs that the engine

<hr width=100% size=1>Def: Yachting - a way of spending the kids inheritance

 

[brianrunyard]

I've replaced the Lucas ACR17 on my Volvo aq110 with an alternator from a Montego. Had no problem with the fittings or aligning the pulleys.

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[cliff]

For what it is worth, forget engine speed - that is not really important

ACR alternators have a max design speed (continous operation) of 15,000 rpm, that is alternator RPM, so if your little diesel does 3500 rpm max you need something like a 4:1 ratio (15000/3500:1 or 4.285714:1) so a 2" alternator pulley should run of an 8½" crankshaft pulley (diameters should be read as PCD not OD).

The setup on my engine is approximately 5:1 ratio.

Don't rely on the riveted type pulley - they cannot transmit the power for very long before breaking up.

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[huldah]

Hi William_H

Thanks for the advice ref alternator.

The battery voltage, when charging various batteries, is now 14 volts, and after a rest period the batteries read in excess of 12.6 volts.

I did not want to complicate things by giving too many details. However, the boat has been owned by the same person for over 25 years. Maintenance has been good except for wiring, an abomination beyond belief. The switches were connected by twisted wires and none of the instruments were connected correctly. (The oil light only came on when the engine was running). The following edited phone calls from my daughter may help.

Dad, you know that old wooden river boat you told me not.................. I have bought it.

Dad, why does smoke pour out when I connect the battery?

Dad, why have all the fuses been changed to 35 amp?

Dad, I have found armfuls of wires, many burnt and bare, behind the controls.

Dad, I have decided to change my job, can you travel to London each weekend and repair her and arrange survey etc.

Daughters, don't you just love ‘em

Philip

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[alb40]

Thanks for all your replies.

The 35 alternator is not powerful enough as is is charging a bank of 2 x 110ah batteries plus one 90ah starting battery - a total of 310ah. The is nothing wrong with the alternator, but as the bearings have some play i thought id upgrade at the same time. I already have a bigger crank pulley fitted but im not sure what ratio this gives to the alternator speed.

Also, as a live aboard i run plenty of lights, stereo, tv, fridge etc. which can mean a long period onboard when crusing means at least 3 hours a day running to charge the bank up. The engine is noisy and vibrates so id like to run for as short as possible whilsty getting maximum charge, as its uncomfortable to run when running the engine whilst moored.

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[cliff]

See my posting above for determining alternator rpm. If you still are not sure how to go about it PM me with pulley details OD, belt type and size.

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[pvb]

You really need a smart regulator...

Your charging efficiency won't be improved much by simply fitting a bigger alternator - you need to add a smart regulator to minimise the charging time. You'll notice a big improvement in charging efficiency once you fit a smart regulator.

As you're living aboard, I'd reckon your 2x110Ah domestic bank is much too small; you could usefully double it in size and this would probably be the most cost-effective improvement you could make. A bigger battery bank will recharge more quickly, could allow longer periods between recharging and, by reducing the depth of discharge of the batteries, could improve their life expectancy.

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