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  #1  
Old 09-07-2009
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2nd Alternator

Hi Guys
I have a Bukh 20hp diesel which at present has an alternator permanently wired to the engine battery and a second 'House' battery that can be connected to the engine battery to charge while the engine is running. I have bought another alternator from a breakers yard and I am hoping to fit it so it can charge the house battery. The alternator has three terminals of which only two were used on the doner vehicle (a Ford Sierra) there is a heavy wire which I guess is the main charge wire and a very thin one, is this the one for the warning light? I am also aware that the negative will have to be connected to the engine.
What is the best way to wire the alternator in and will I need a relay to isolate the supply when the ignition switch is off. Also on the Bukh engine when switching off, the ignition switch goes to the off position and then you have to push the key in and turn it further backwards to operate the stop solenoid, I know it is not good to turn off the alternator circuit if the engine running and I would like to avoid frying my new alternator . Any suggestiond will be gratefully received.
cheers Jamie
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Old 09-09-2009
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Hello Cacique,

I'm on the same predicament (2nd alternator). I would recommend you to check the Balmar's website (they have a useful FAQ section and have put together a .pdf file which will help you with your installation.

In addition I attach a response e-mail of their technical department which can be enlightening for you.

START QUOTE
PART I
You've bitten off quite a project. A 300 amp bank of AGM batteries ideally needs a 135 amp alternator to properly charge this size bank. You could use our 6 series alternator in the 120 amp version. This alternator requires dual 3/8" (10mm) belts to properly drive it. You can use a single 10mm belt on alternators up to 80 amps but anything bigger than that needs the additional width to survive. You will have to have a special dual belt pulley machined up to mount a second alternator. Any mount you fabricate will have to be built so the proverbial 300 pound gorilla can jump on it without damage to the mount.
fficeffice" />>>
The second alternator must be mounted on the opposite side of the engine from the current alternator to avoid stressing the crankshaft. Modern high speed diesels have very delicate crankshafts that can easily by damaged or broken if they are improperly stressed. I would duplicate the Volvo mount as closely as possible as they have already done the necessary engineering and location studies,
>>
PART II


I would rather see you get this right the first time rather than damage your engine.
>>
6mm bolts certainly aren't much to hold a good quality mount but they must have confidence in them. The major issue is to offset the dynamic load as much as possible and "balance" it by having the alternators mounted one to a side as close to being directly opposite each other. If one side has the alternator mounted high, the other one should be mounted low on the other side. On most engines, it is a good idea to mount no more than 15ļ above or below the horizontal centerline of the crankshaft.
>>
One of the issues common to a lot of small diesels is the size of the circulator water pump bearing. It is not large enough to accept the increased side loads of high output alternators or increased belt sizes or numbers. That is one of the reasons for the 80 amp limit.
>>
Don't get me wrong. You can charge your AGM batteries with a smaller alternator but it will take longer so you lose part of the advantage of the AGM's rapid charging capability. The 100 amp alternator can get along nicely with a single one half inch (13mm) belt if you use a top quality belt and keep it properly tensioned. The 6 series 621 model will fit your bracket if you are using a single one inch or two inch main mounting foot alternator. This alternator is available in an attractively priced kit that includes the alternator, voltage regulator along with battery and alternator temperature sensors. Wither of our popular regulators will work with your batteries as they are programmable to the type of batteries used. You would probably want to use the ARS-5-H regulator. The is kit's part number is 621-VUP-100-SR-KIT be found online for around $850. List price is $1199.95.
>>
>END QUOTE>
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Old 09-09-2009
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hello cacique
While you don't explain battery size or usage, the start battery is seldom down much as starting uses such a small # of amp/hours. By far your best bet would be to go with only 1 alternator, the best of the 2, and wire it direct to the house bank along with your other charging sources. Buy a Xantrex Echocharge to keep your start battery topped up - an easy job. It will save you a great deal of custom fabrication and complexity as well as save wear and tear on your engine. Wire the alternator output direct to the house bank, not through a selector switch. That way you cannot fry diodes whatsoever, and your selector switch determines use not charge direction. The Echocharge has 3 wires - one to house +, onre to start +, and a ground wire. It is a solid state device and reliable and maintenance free. Your start battery will be topped up very quickly after the engine is started as you are only using less than 3 amp/hours to start it. This is probably one of the most reliable, foolproof systems you can have.
Brian
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Old 09-14-2009
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2nd alternator

Thanks for the idea but $125 from the US probably $225 to me in the UK is way over my buget, I've spent approx $20 for the alternator and can manufacture the mount myself, its just the connections to the house battery I need to get right, then the engine alternator will take care of the engine battery and the second alternator will take care of the house battery and I won't have to worry about switches and running down the engine battery ever again, so does anyone know what is the best way to wire it up?
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Old 09-14-2009
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Quote:
Originally Posted by cacique1977 View Post
Thanks for the idea but $125 from the US probably $225 to me in the UK is way over my buget, I've spent approx $20 for the alternator and can manufacture the mount myself, its just the connections to the house battery I need to get right, then the engine alternator will take care of the engine battery and the second alternator will take care of the house battery and I won't have to worry about switches and running down the engine battery ever again, so does anyone know what is the best way to wire it up?
Or you can pull a alt off of any disco/range rover all of those are 125-140 amp and a two wire hook up.
I could show you how to wire it but i have no clue what a Fore sierra is?
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Old 09-14-2009
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Hello cacique
You would wire it the same way as the other alternator is wired, but to the house bank. The batteries would be kept totally separate except for the ground. The heavy wire would be the output to battery +, the thin wire would probably go to the warning light for excite. Ground is obvious but all grounds should go to the same point on the block. As long as the output wire is connected to battery + either it will work or not but no damage can be done. I don't think you will need a relay as long as both banks of batteries are always kept separate.
Brian
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Old 09-15-2009
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Here's a link to the best source of alternator information I know of - the 12 volt Doctor's alternator handbook. http://kb-kbh.dk/shipslib/el_ombord/...ndbook_ocr.pdf
The whole book is there from wiring various types to what makes them tick.
The wiring diagrams for the different types are after page 60 or thereabouts. It's a good reference to keep on your computer for future use.
Hope this helps.
Brian
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Old 09-15-2009
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Overstress the crank?

He's talking about a 20hp Bukh, most likely the DV20. Balance is important, but over-stress? Not likely. Those things are built for long, hard lives at sea.
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Old 09-16-2009
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Thank you Mitiempo
This manual looks like it's just what I need.
Very Happy
Cheers Jamie
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Old 01-17-2011
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well I bought an alternator from a scrapyard for £15 ie less than $20 US
I made a bracket and used a flat type belt to drive it from the outside of the main flywheel. I managed to get a large diameter pulley for the alternator so it wouldn't run overspeed from my local motor electrics dealer for £3 (US $4). I have wired in the second alternator with an isolating solenoid so when the ignition switch is turned on the 2nd alternator is 'in circuit, I have also added an indicator light so it illuminates if it is not charging.
So far It has been in use for the full season and has worked really well, I have gone from constantly worrying that the engine battery would be too low to start the engine to now being totally at ease and not even worrying if the cabin lights are used.
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