Regulator bypass circuit

[kiwikol]

I'm sure this has been discussed before but I can't find it nor the confidence I need to do the work !
I have an article referring to by-passing the regulator and feeding the alternator's full field current into the alternator, which in turn will pump out it's full capacity, the purpose being to avoid the miniscule charge that so often is provided when you actually need a good boost to initially charge a 'dead' battery. The article obviously suggests a big red warning lamp to let you know it's on boost charge and warns about watching the voltmeter "like a hawk". Basically it involves a three way switch between the regulator (f terminal) and the alternator, position 1 giving normal regulated field current, position 2 unregulated current direct from the battery, and position 3 no current to allow the alternator to spin freely.
Can anyone advise whether this has any (un-mentioned) traps for the electrically unqualified diy-er such as myself? I am attempting to try it on a Yanmar 3JH3 with a Hitachi 55A alternator.
Maybe I could attach a pic of the circuit if I can find out how to include it here?

 

[roly_voya]

On a good day you could destroy the batteries, burn out the alternator and set fire to the boat. On a bad day it might explode. This is a seriously bad idea that should only be done as either an alternator test, a means of re-energising the coils or if the regulator has blown and you absolutely have to get some charge into a battery but only as a temp measure, never permenantly wired in.
Get an alternastor controller, simple to fit and will pay for itself in fuel saved and extended batt life

 

[ytd]

I have done this in an emergency and got away with it but you really have to watch the alternator temperature and the state of the fan belt. The alternator got too hot to touch and the fan belt had started to melt with the inside of the engine box coated in ribber bits.

 

[halcyon]

Normally the regulator does not control rotor ( field ) current, as in reducing rotor current. The regulator monitors voltage on the alternator output, then turns on or off the ground to the rotor, thus turning on or off alternator output to limit voltage. The rotor is feed from the field diode / diodes, and earthed by the regulator. So by-passing the regulator to ground, will only run alternator on over voltage, this can be 100's of volts.

Your gamble.

Brian

 

[lw395]

When you say a dead battery, do you mean merely flat or damaged/old/sulphated?

Boosting the volts to 15 or so to fast charge a battery is one thing, overheating the alternator with very high current is totally different. Most boost controllers will ramp the volts slowly to keep the current reasonable, avoiding shortening the life of the alternator through overheating, rapid fan belt wear etc.
If a battery is dead, as in not storing energy in its cells, and you stuff a kilowatt into it, it will get very hot quite quickly!
The chance of explosion is very real.
If the battery is just flat, a current limited charger should be allowed to bring it up to say 13V for a while before trying to get any serious charge in.
If a battery has been very discharged, it may be wise to monitor its temperature when charging it the next couple of times.
Take care,

 

[kiwikol]

Very much appreciate all the advice - and warnings! What I am after is a way of avoiding the frustration of watching the donk burning diesel dollars for the sake of a few miserable amps when the battery is down to perhaps below 12v (not 'dead' but definitely needing a boost which normal engine running doesn't seem to do in a reasonable space of time.
roly_voya.... what is the 'alternator controller' you mentioned? Haven't come across that but sounds interesting.
lw395....what is 'a current limited charger' ?
Like I said , I'm a bit green but thankful you are all out there looking after me and perhaps avoiding having to rescue me! Much appreciated

 

[RobBrown]

Try a google search for alternator regulators

here are links to some of the most commonly encountered ones in the UK:

http://www.sterling-power.com/products-altreg-info.htm
http://www.adverc.co.uk/technical/technical-faq.asp
http://www.power-store.com/view-item.asp?itemid=1288

 

[lw395]

A current limited charger, is: ( in this context)
A small battery charger that only does a couple of amps
A solar panel
A voltage source with resistance
or a lab power supply with the current limit set to something sensible.
In fact most charging sources apart from a big alternator, where the battery will be doing the limiting!

 

[VicMallows]

I do not agree with the doomsayers on this, but would certainly caution that you must know exactly what you are doing.

Firstly, you need to make a contact to one of the brushes, in exactly the same way as you would have to if fitting a commercial 'smart' regulator. On many alternators this will involve opening the alternator.

Precise electrical details of the bypass will differ depending on whether the alternator is 'P' or ''N' type, but you will end up bypassing the existing regulator with a high-wattage resistor in the region of 2-10 ohms.....this needs to be variable in some way.

It's then just a case of monitoring the current to keep it at a safe level for both the battery and the alternator; and the voltage to make sure you don't blow any other electrical stuff you have left on.

I have just such an arrangement charging away right now!!......but by now you may have decided to fork out for the commercial regulator!!


/forums/images/graemlins/smirk.gif

Vic

 

[kiwikol]

Sorry for the delay folks - I'm suffering from information overload and have to digest it all with due considerations to the consequences! Meanwhile, may I thank you all for your input - it is really appreciated - I now just have to decide which way to go (to ensure it doesn't have a downward component!!)