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30 amp ammeter

Howard

Well Known and Active Forum Website User
VOC Member
I’ve fitted a 30 amp alternator on the Egli. Unfortunately it doesn’t have a fitting for a charging warning light, and my ammeter is only good for 8 amps.

Does anyone know where I can find a 30 amp 1 ½” diameter ammeter. Or can I fit a resistor across the 8 amp ammeter (I only need to know it’s charging, not how many amps).

H
 

b'knighted

Well Known and Active Forum Website User
VOC Member
Hi Howard,

My elecrrical advisor and Vincent Mentor, RogerClarke, insisted on wiring the high output alternator that he fitted during my Knight rebuild, directly to the battery. He advised me that should the link between alternator and battery fail, the alternator output voltage can run away and destroy the alternator. He had previously shunted the ammeter for use with a Fiat dynamo. To show battery condition and charge effectiveness I have fitted a BSM (battery Status Monitor) LED wired off the ignition circuit. It has two wires and is simply connected from live to earth. Whenfirst switched on it cycles through its colours with slow flashing red showing low voltage, amber showing good static voltage, green showing charging and fast flashing showing overcharging. As a 5mm LED it is easy to hide ( I have one discreetly fitted between headlamp and headlamp bracket on a Comet) and easy to wire. Mine are from Alan Osborne (http://www.aoservices.co.uk/data/bsm.htm) who also makes things like the Vreg. Other makes are available (see ebay item 200627678428 and others) but I have only used the AO Services version.

Kung Hai Fat Choi!
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Howard, I was told I needed a 30 amp for my Dougleator from USA, But I've never seen it move more than about 8 ish, I wonder if you could get away with a smaller one ?. I got mine from a triumph dealer in west london, Good Luck Bill.
 

Alan J

Well Known and Active Forum Website User
VOC Member
When I went to 12 volts and 180 a.m.p.s I just "bridged across the ammeter with a piece of copper wire-now the meter moves about half-been there for years with no bad effects.
 

timetraveller

Well Known and Active Forum Website User
VOC Member
I think that Alan J means 180 watts or otherwise he could do a bit of welding while out and about. The standard Walkernator can produce up to 30 amps, and an experimental one on test now can produce 40 amps, and although a 12 volt system is nominally 12 volts in reality while running the volts tend to be about 14.3 thus over 400 watts can be available. However, so far no one has found the need to fit a 30 amp ammeter. What happens is that once the bike is started the ammeter tends to go right over to full charge. If one then hold the bike on tick over for a few seconds the output from the alternator is sufficiently low, due to the low engine revs, that the alternator is not able to produce the high rate of charge. The amps drop progressively down as the battery volts build up to the 14.3 volt level. Typically this takes seconds, or if the battery is really flat then a charge of about 6 amps continues to be shown. Once the amps reading has dropped to this level then one can use as many revs as one wishes and the 8, 10 or 12 amp ammeter being used is well able to take care of any passing charge. The rather small batteries used on bikes charge up very quickly when a few amps are fed into them and very quickly achieve a sufficiently high voltage that the charge rate drops. What can cause trouble is a dud battery. If you have a worn out battery which cannot attain its full voltage of 14+ volts then the system continues to belt out large numbers of amps to try to bring up the battery voltage and if the ammeter cannot cope with these then something will fail.
B’knighted’s comments above are correct in that when using an ammeter all the charging current has to go up to the front of the bike and then back to the battery. It is better practice to feed the battery direct and then use a volt meter, or LED system, to indicate battery volts. My trouble is that having been brought up in the era of ammeters I find it very comforting to be able to glance at the front of the bike and see at once just what is happening with all those electrons which I cannot see, but can feel if there are enough of them!!
 

Howard

Well Known and Active Forum Website User
VOC Member
Thanks all. I think that gives me enough answers for now.

TT, I'm with you, there's something about an ammeter that LEDs just can't compare with.

Ian, I haven't finished the alternator conversion yet, so you got me thinking - I checked the wiring when I got home and I've already connected the alternator direct to the battery as you suggest ................ That means the ammeter would only read discharge anyway ............... It was cold in the garage at the weekend and my brain wasn't up to full speed!!!!

Bill, the wife says I've been getting away with a smaller one for years! (I wonder how she knows?)

H
 

timetraveller

Well Known and Active Forum Website User
VOC Member
This "bit of copper wire" is known as a 'shunt' in the trade and by varying its resistance it is possible to make any small ammeter have a different full scale value from that on the meter itself. Possibly best to read up about these in any elementary book on electrics or try Google or Wikipedia.
 
Last edited:

Comet Rider

Well Known and Active Forum Website User
VOC Member
Just to add my 10p worth (inflation you know :) )

On my Comet special, with Walkernator, I have a 30-0-30 Ammeter I got off eBlag for approx. £15 :rolleyes:
At startup I see a +ve charge of anything upto 15A, but by the time I have got less than 100 yards down the road it is less than 4-5 A
I have the Comet setup for a fast tickover, and when all has settled it will balance lights and ignition on tickover ( HID and LED lights and coil ign)

I have run a DVM on the bike to enable monitoring the charging voltage, and providing all is well wired (correct spec on the high powered stuff, as well as proper grounding) I see a max of 14.2 Vdc across the battery.

HTH
Neil
 
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