Fitting an ammeter

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GreekYiannis

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I'm out in Greece on a tiny island running a Colvic 20 with a Bukh 20 diesel engine. Recently, my red charging light konked out. The local electrical guy put a meter across the terminals of the red light and pronounced it 'Kaput'. My battery does not run down, so I think the charging circuit is working. I ordered an ammeter and thought I could simply substitute it for the red light.
My problem is that when I connected it and started the engine, the needle didn't move. i reversed the wires to the ammeter terminals and that did nothing either.
My alternator is old but it seems to work.
Question: How can I test the charging circuit?
Equipment I have is - I have a new Excel XL830L multimeter but that is new and strange to me and seems to only go up to 10 Amps.

Am I missing something? HELP
 
The ammeter won't do anything in place of the light, that is not the main charging circuit, it's energising the field coils, 'kickstarting' the alternator. You should replace the red light with similar. Although the alternator should work in this position that's co-incidence and you should remove it ASAP. Although your ammeter will measure the current to the field coils that's of the order of .25A (light lit) to 0 (light out) and measuring it doesn't tell you anything.

The easy way to tell if it's charging. is to use your meter on volts range. Measure volts across the battery before starting the engine, then measure volts after starting the engine, it should be higher, somewhere around 13.3V rising over time to 14.4V. The main thing is that it's higher than your battery before starting the engine which will be (hopefully) between 12.0 and 12.8V

Can you link to the ammeter, it is generally not recommended to put moving coil (old-style) ammeters in charging circuits these days. (or... does it have a needle?)

Can you send it back?

You would be better off with a shunt (digital) ammeter (search on eBay) but as I say above, the simple check for charging is by measuring the voltage.
 
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You might find it useful to take a look at the Boat Electrical notes on Tony Brooks' TB-training website.
http://www.tb-training.co.uk/

All basic stuff which should help you to understand a little more about the use of meters and how the alternator works along with most other aspects of boat electrics
 
Thanks very much Chris. I'll do that.
I would like to have the ammeter working. You mention "energising the field coils, 'kickstarting' the alternator" but that doesn't mean anything to me. Could you explain it in simpler language for me?
Many thanks again.
 
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GreekYiannis said:
Thanks very much. I'll do that.
I would like to have the ammeter working. You mention "energising the field coils, 'kickstarting' the alternator" but that doesn't mean anything to me. Could you explain it in simpler language for me?
Many thanks again.
Click to expand...

Look at my link to tb-training Its all there and explained simply.
 
The light before the engine is started connects a small current (limited be the size of the light) to the IND terminal of the alternator (ie not the main output). Once the alternator is working this current is no longer needed and the light goes out.

To use your ammeter you need it in the fat wire from the alternator. This involves running said fat wire to the panel and back - an unnecessary length of cable can cause voltage drop. So normally in a modern installation you would have a shunt near the batteries and a digital meter on the panel.

something like this link

though if you are stuck with the one you've got then use 10 -16mm2 cable to connect it and keep the cable run as short as possible
 
Chris Pink said:
The light before the engine is started connects a small current (limited be the size of the light) to the IND terminal of the alternator (ie not the main output). Once the alternator is working this current is no longer needed and the light goes out.

To use your ammeter you need it in the fat wire from the alternator. This involves running said fat wire to the panel and back - an unnecessary length of cable can cause voltage drop. So normally in a modern installation you would have a shunt near the batteries and a digital meter on the panel.

something like http://www.ebay.co.uk/itm/100A-5-Wi..._Measurement_Equipment_ET&hash=item3cd2c27b56

though if you are stuck with the one you've got then use 10 -16mm2 cable to connect it and keep the cable run as short as possible
Click to expand...
The alternator outputs 12v pos & cancels the light as its now fed via 2 x 12v pos wires
 
Very much obliged Chris. That's added a lot to my understanding. I think I'll ditch the £4.99 Ammeter as a mistake and buy an electronic shunted one in the UK. But fitting it will be on next year's list.
I am truly grateful for all the help I get on this Forum when I'm out here.
 
Chris. Your figures were spot-on. I got a reading which rose to 12.86 before starting the engine, and another which rose to 14.4 after starting. What a relief it was to know that my battery is being charged.
You asked, so I will mention that my ammeter does have a needle. Its range is 0 - 30 Amps, its class is 2.5 (which I think is a measure of accuracy ie within 2.5% of true) and its made by HUA. I'd appreciate any comments on my 'needle' ammeter before buying an electronic one.
Many thanks again. I'll be reading about simple boat electrical circuits today (thanks to Vic for that link).
 
Your warning light on this engine is one of three LEDs ie, alt water and oil light, this is driven by a small circuit board behind the panel. if the led. fails your alt, should still charge, very complicated method in my opinion, last winter spent rewiring the complete engine only to find this board was defective, ended up with new conventional instrument's and warning light system. as the cost for new instruments and board was horrific.
 
Thank you for that helpful advice. I can't see a circuit board on mine. Just a lot of wires coming from the start switch. I have an engine temp gauge fitted which works well, so I disconnected that light. I had an oil gauge so i disconnected that light too. But then I had a problem with dripping from the oil gauge, so now I just check my oil a lot and listen to my engine for signs of any drop in pressure. So the little red light was the last one left. Now the bulb has blown so I'm going to get a digital ammeter and shunt - which I've been learning about today. That means all three of the original lights will be gone - indeed have gone. Some day I'll re-wire the whole boat, but I'm putting that off as I'd rather be fishing.
 
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Yiannis,

You seem to be getting there.

The alternator red light is connected between a feed taken from the output of the alternator, and the 12v. battery positive. It is a very low current, high resistance, bulb. When the power to the engine is switched on, there is no output from the alternator, so this will be near zero volts. As the charging voltage builds and rises to something over around 13.5 volts, the difference in voltage driving the lamp becomes negligible, so the light goes out, thus indicating that all is well.

What you do NOT want is a low resistance ammeter stuck in circuit instead of the bulb: as you have found this does not work, as the circuit feeding it is relatively high voltage, and in extremis could possibly be damaged.

What you really need is one of the normally shunt-driven battery state meters available on the market. Votronic do a nice one. The shunt is inserted in the common negative lead to the battery. It is a very high current resistor capable of taking e.g. 100A and is tapped off with leads from each side of it, so that the instrument can detect the very small voltage drop across it. The greater the current, the greater the voltage drop (Ohms Law). The instrument is also connected to the battery positive, so that it can measure battery voltage. You now have the ability to read the voltage, the current, and most importantly, the ampere-hours (AH) used, so that you can monitor the state of your battery.

Using your cheap ammeter in circuit would not achieve the same. The shunt built into it (they all have one) is probably only built to withstand 30A, so you will have a possibly high insertion resistance, and hence voltage loss. It may well not be able to withstand starter motor currents, or if the batteries are down, higher charge rates from your alternator.

I hope this helps..
 
GreekYiannis said:
Now the bulb has blown so I'm going to get a digital ammeter and shunt - which I've been learning about today. That means all three of the original lights will be gone - indeed have gone..
Click to expand...


Just one point. Even with an ammeter the alternator needs the light to function. If the light fails the alternator stops working (as you have seen).

Syfuga is partially right though too low a current (high resistance, low wattage bulb) can make the alternator difficult to excite (start). A lot of slow revving engines need to be revved hard to make the light go out and the solution is to fit a lower resistance (higher wattage) bulb. For this reason LEDs are generally unsuitable for alternator warning lights.

So put the alternator light back. It is a useful quick check of alternator function and although there are other ways of supplying the initial excitation current the light is the simplest.


Just to waffle on a bit, for others who may be in the same situation: if the bulb blows, a quick fix is to short the bulb wires together. Leaving them like this does hold the risk of blowing diodes in the regulator. I prefer, in this get-me-home situation to simple touch the wires together. It is also worth noting that some split charge relays get their power from the alternator side of this bulb.
 
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I had a look at the external shunt digital voltmeters on ebay.

can you get one which shows both charging and discharging amperage.

I know a proper battery state unit is better but they are a factor of 10 more expensive
 
most of them will show negative as well as positive current. The one I linked too was a lazy example and I didn't read its spec in detail.

The most important thing is that it can run off the power it is measuring (that one could)
 
Thank you Syfuga for a brilliant reply. That is very helpful indeed. I like the look of the Votronic meter and its functions but unfortunately Votronic seem to have only one supplier in the UK [RoadPro Ltd] who don't stock the item. But I guess that any digital 100 Amp capacity Ammeter and shunt will give me a reading. So I'll try Amazon UK. I will also be sure to try to buy something with a drawing which hasn't been translated out of Korean into Portuguese and then into English.
Many thanks again.
 
David. There's some confusion in your message. As far as I know, voltmeters don't need a shunt. Only ammeters do. I'm looking at combined ammeter and voltmeters on ebay at reasonable prices but i don't know if the pros would recommend them. The Votronic one recommended by syfuga above looks fabulous, but is not in stock in the UK and may be very expensive.
 
GreekYiannis said:
David. There's some confusion in your message. As far as I know, voltmeters don't need a shunt. Only ammeters do. I'm looking at combined ammeter and voltmeters on ebay at reasonable prices but i don't know if the pros would recommend them. The Votronic one recommended by syfuga above looks fabulous, but is not in stock in the UK and may be very expensive.
Click to expand...

You don't have to cut wires to fit a shunt either, for ref

http://www.kddpowercentre.co.uk/data/15.pdf


Brian
 
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