Measuring charge from Outboard

[coveman]

I have an 8hp Yamaha 2 stroke with charging kit - Could someone point me in the right direction to check that there is an output and that the charging circuit is working correctly.
There are two leisure batteries on the boat with a "1" "2" "both" switch. I thought if I measured the voltage with a multi meter across the positive and negative terminals of the appropriate battery I should see some difference when the input from the engine is connected. However the voltage remains constant at 12.6v whether the input from the motor is connected or not.
This leads me to believe there is a problem with the charging from the motor or have I missed something?
I have also been told that if the engine is run without the charging circuit being connected then damage to the rectifier can result , but not sure if this is true.
I also have a good solar panel which works well, but it would be good to have the outboard circuit as a back up even though the output from a small outboard is somewhat limited.
Thanks in advance for any help

 

[RichardS]

Provided that the switch is in the correct position, I would have thought that you would expect to see a voltage increase when the outboard is running.

You could simply connect the multimeter across the outboard output without the batteries and start the engine for a few seconds to see if any voltage is produced. It should not harm the rectifier.

Richard

 

[William_H]

The most useful way to check charge is with an amp meter. This requires you break the line and insert the amp meter. You can use a digital multimeter however I think the old analogue meters are better. You can buy a cheap one and permanently wire it in. It can be useful when checking solar charge as well. A digital meter can give strange results because the charge current will be a series of pulses of current. The meter samples for a short period and this sample time may or may not correspond to the pulse of current. Likewise when measuring voltage with no battery connected.
Some outboards have quite miserable charge capability. Indeed the old Johnson/Evinrude called their's a lighting coil and was meant to support boat lights. As such it battled to provide enough voltage to actually charge a 12v battery. I could only get a charge current via a rectifier at pretty high motor RPM. So conceivably yours may be doing as well as can be hoped for. I made up a replacement rectifier using Schotky diodes with lower volt drop which did improve charge current a little. But ultimately I gave it all away as a bad thing. ol'will

 

[NorthUp]

Small outboards often do not have a voltage regulator in the circuit, relying on a connected battery to bring the voltage down to a reasonable level. Also, engine revs are needed to bring volts up. Without a battery connected you can find. 50-60v AC at the rectifier input, at full revs, enough to fry a cheap one
Disconnect. the rectifier input and. check for. AC voltage at a fast idle, reconnect and the rectifier output should be DCvolts. No AC and its. probably a faulty coil under the. flywheel, no DC change the. rectifier.

ps nexus keyboard trouble...hence extra full stops!

 

[QBhoy]

Hi
These small outboards only have a tiny output. Not a proper charging system like your car would have. It’s just a stator with a tiny rectifier. Will only throw out late 12’s or 13v if lucky and only when at a fair bit of throttle or revs. Enough to trickle charge a battery or float the voltage. You are testing correctly in its simplest form. Try opening the throttle a bit and test the voltage. If there is any doubt, disconnect the output leads from battery and test.

 

[lw395]

Hi
These small outboards only have a tiny output. Not a proper charging system like your car would have. It’s just a stator with a tiny rectifier. Will only throw out late 12’s or 13v if lucky and only when at a fair bit of throttle or revs. Enough to trickle charge a battery or float the voltage. You are testing correctly in its simplest form. Try opening the throttle a bit and test the voltage. If there is any doubt, disconnect the output leads from battery and test.

We've got a small Yamaha with a charging output, it's actually IIRC 70W according to the manual.
That's enough to run some lights, top up the battery for the VHF etc.
You don't need huge rpm for the charge to start.
Lots of video on youtube about how to test.
Key points are:
Check the coil has continuity but isn't grounded.
Look for AC volts when running- could be quite high unloaded, like 40+ volts!
Check the rectifier actually looks like a diode bridge
Check DC volts and current into a battery.

Some people use a combined regulator-rectifier from a motorbike. But you don't really need a regulator if you have a fair size battery and don't do motoring for hours on end regularly.

 

[John the kiwi]

My 15 Hp Honda had a charging circuit with zero output.
I learned that it most probably would have been killed by being disconnected from the battery while the engine was running.
I was easily able to measure AC voltage to the input side of the the rectifier, but nothing coming out.
Quoted replacement price was unpalatable.
I took the AC output to a small box on the boat and fitted a bridge rectifier and importantly a large capacitor across the DC side.
Has worked well for several years and delivers a useful amount of charge. It has no charge controller, but the 9 year old house battery seems OK with that situation!

 

[coveman]

Thanks for the replies - the motor is a saildrive version and does indeed have a rectifier fitted so I would expect it to do some charging. However it is possible that it has been run disconnected from the battery which I am told may have damaged it. I have very little knowledge of "electrics" so can't say whether this opinion is correct.
It would seem odd that if a saildrive version was bought it would HAVE to be fitted to a battery - surely that would be optional, as some boaters may not want to use the charging facility.

In fact since writing this I contacted my Yamaha Dealer who tells me it should do no damage unless it is run like this for exceptionally long periods.

 

[lw395]

Thanks for the replies - the motor is a saildrive version and does indeed have a rectifier fitted so I would expect it to do some charging. However it is possible that it has been run disconnected from the battery which I am told may have damaged it. I have very little knowledge of "electrics" so can't say whether this opinion is correct.
It would seem odd that if a saildrive version was bought it would HAVE to be fitted to a battery - surely that would be optional, as some boaters may not want to use the charging facility.

In fact since writing this I contacted my Yamaha Dealer who tells me it should do no damage unless it is run like this for exceptionally long periods.

There's not much excuse for running open circuit to do any damage. A 1000V bridge rec costs about a quid.

 

[coveman]

There's not much excuse for running open circuit to do any damage. A 1000V bridge rec costs about a quid.

Sorry could you explain to an electrics "dummy" what a "bridge rec" is?!

 

[RichardS]

However it is possible that it has been run disconnected from the battery which I am told may have damaged it. I have very little knowledge of "electrics" so can't say whether this opinion is correct.

In fact since writing this I contacted my Yamaha Dealer who tells me it should do no damage unless it is run like this for exceptionally long periods.

Indeed. It's suddenly disconnecting whilst actually running the engine and charging the battery which might cause damage. Simply starting and running without the battery even being connected is not going to cause a problem.

Richard

 

[VicS]

Indeed. It's suddenly disconnecting whilst actually running the engine and charging the battery which might cause damage. Simply starting and running without the battery even being connected is not going to cause a problem.

Richard

True.

The other thing that will fry a rectifier instantly is connecting the battery with the polarity reversed.

 

[VicS]

Sorry could you explain to an electrics "dummy" what a "bridge rec" is?!

He means "bridge rectifier"

Its the name given to the type of rectifier used which contains, in your case, 4 diodes.

You have a choice between buying one with a suitable " peak inverse volts" ( PIV) and current ratings from an electronics component supplier for about a £1, making it fit and adapting the wiring to connect it.

OR

buying a replacement part for your engine, which will cost an arm and a leg but will fit exactly in place of the original and connect to the existing wiring.

 

[coveman]

He means "bridge rectifier"

Its the name given to the type of rectifier used which contains, in your case, 4 diodes.

You have a choice between buying one with a suitable " peak inverse volts" ( PIV) and current ratings from an electronics component supplier for about a £1, making it fit and adapting the wiring to connect it.

OR

buying a replacement part for your engine, which will cost an arm and a leg but will fit exactly in place of the original and connect to the existing wiring.

I presume this is the replacement part if the rectifier is knackered, rather than some form of cure for running the engine disconnected?

 

[lw395]

Indeed. It's suddenly disconnecting whilst actually running the engine and charging the battery which might cause damage. Simply starting and running without the battery even being connected is not going to cause a problem.

Richard

If Yamaha say it might, maybe I'd take their word for it.
We don't know exactly what's in their module.
There could be other parts related to suppression which might have an effect.
But I would start with the basics and check out the coil.

 

[lw395]

I presume this is the replacement part if the rectifier is knackered, rather than some form of cure for running the engine disconnected?

Yes.

 

[RichardS]

If Yamaha say it might, maybe I'd take their word for it.
We don't know exactly what's in their module.
There could be other parts related to suppression which might have an effect.

"In fact since writing this I contacted my Yamaha Dealer who tells me it should do no damage unless it is run like this for exceptionally long periods"

Richard

 

[lw395]

"In fact since writing this I contacted my Yamaha Dealer who tells me it should do no damage unless it is run like this for exceptionally long periods"

Richard

That did seem a little strange to me.
What's an exceptionally long period in this context?
It's a small box of electronics. If it survives being used in any particular way at full temperature for an hour, things like this normally last a very long time. I've blown up a lot of electronics in my time, a lot of times it's all over in microseconds. Some things take a minute or two to heat up and keel over. Most things of this kind of size and simplicity reach a steady state in a few minutes. Once the enclosure they're placed in is up to heat of course, which might be a few minutes of hard running for a medium sized outboard? So if it survives that, what is the failure mechanism related to being off-load, which comes into play in a 'long period'?

 

[RichardS]

Simply starting and running without the battery even being connected is not going to cause a problem.

Richard

If Yamaha say it might, maybe I'd take their word for it.

"In fact since writing this I contacted my Yamaha Dealer who tells me it should do no damage unless it is run like this for exceptionally long periods"

Richard

That did seem a little strange to me.

What seems a little strange to me is your comment that "If Yamaha say it might, maybe I'd take their word for it." as that's exactly what I'm advocating.

Richard

 

[lw395]

What I'd advocate is to work out which bit isn't working, then get it working.
If the problem is the rectifier/regulator, we won't know if it died due to being run open circuit, due to poor design, or being overloaded, shorted out, battery wrong way around etc.