Electrical charging question

[Cheshire cat]

I'm gritting my teeth in anticipation whilst typing this question.

 

I have watched the heated debate regarding Smartgauge versus BMV with some amusement. I'm quite happy to let you heavyweights slug it out but I've got a related question I'd like to ask.

 

We have a share in a boat and between us we've managed to kill a set of batteries in nine months. The previous set lasted three years so either our habits have changed dramatically or we have a fault that we haven't noticed early enough somewhere on the charging circuit.

 

I had the alternator tested by Middletons in Manchester (recommended to me by the late Tim Leech) and it has been given a clean bill of health.

 

That caused me to think that maybe the belt was slipping or there is a bad connection and no-one has noticed. I'm not sure we want to spend £180.00 on a BMV so I was thinking of a simple Ammeter with a suitable shunt.The owners are not technically minded so something that simply shows whether we are charging or discharging is probably all we need. Given that the Alternator is capable of pushing out 100 Amps I'm thinking that the resistance of the shunt would be quite small.

 

My question is if the shunt resistance is small will the length of the cables and corresponding resistance of same mess things up.

 

To site the gauge ideally, the cable runs would need to be 2 metres long.

 

What haven't I considered.

 

Thanks

 

Andy

[WotEver]

Hi Andy,

 

Yes, a cheap ammeter will show how well the batteries are charging and will also tell you (with a tiny bit of knowledge) when they are fully charged.

 

The cables from the shunt to the meter carry very little current and can be (within reason) as long as you like. The ammeter should come with instructions specifying suitable cable size.

 

I've kept this brief so you can follow up with any other questions should you wish.

 

Cheers

Tony

 

Oh, one other consideration; you could have killed the batteries by repeatedly discharging them too far. The easiest way to prevent that (or at least to be aware of how discharged they are) is with more kit. Dare I suggest a SmartGauge? But of course that's another £140.

[Top cat]

Yes an ammeter will do what you want but please be aware that some of the cheap digital ones on e-bay only register current in one direction, best to check the spec carefully as you want to know the ins and outs.

 

Top Cat

 

(Edited to add the word digital)

Edited January 22, 2016 by Top cat

[Roger Crown]

I'm gritting my teeth in anticipation whilst typing this question.

 

I have watched the heated debate regarding Smartgauge versus BMV with some amusement. I'm quite happy to let you heavyweights slug it out but I've got a related question I'd like to ask.

 

We have a share in a boat and between us we've managed to kill a set of batteries in nine months. The previous set lasted three years so either our habits have changed dramatically or we have a fault that we haven't noticed early enough somewhere on the charging circuit.

 

I had the alternator tested by Middletons in Manchester (recommended to me by the late Tim Leech) and it has been given a clean bill of health.

 

That caused me to think that maybe the belt was slipping or there is a bad connection and no-one has noticed. I'm not sure we want to spend £180.00 on a BMV so I was thinking of a simple Ammeter with a suitable shunt.The owners are not technically minded so something that simply shows whether we are charging or discharging is probably all we need. Given that the Alternator is capable of pushing out 100 Amps I'm thinking that the resistance of the shunt would be quite small.

 

My question is if the shunt resistance is small will the length of the cables and corresponding resistance of same mess things up.

 

To site the gauge ideally, the cable runs would need to be 2 metres long.

 

What haven't I considered.

 

Thanks

 

Andy

Surely on a share boat the simplest solution would be a Smartgauge, all crews can see easily if they need to charge or not. Plus the voltage indication on each bank gives a basic notion as to if the alternator/s are working. It's also a bit scary if a syndicate cant afford £180 to help maintain their boat.

[Loafer]

Yes an ammeter will do what you want but please be aware that some of the cheap ones on e-bay only register current in one direction, best to check the spec carefully as you want to know the ins and outs.

 

Top Cat

 

Well obviously. If I want to measure current in both directions, I'd buy an ammeter that had a centre zero. Even my missus thought of that!

[WotEver]

Surely on a share boat the simplest solution would be a Smartgauge, all crews can see easily if they need to charge or not. Plus the voltage indication on each bank gives a basic notion as to if the alternator/s are working.

Roger, that was my first thought too, but it's £140. Also, the ridiculous situation currently on this forum makes me wary of even mentioning the 'S' word. I'd hate to see another multi-page argument ensue.

[Tony Brooks]

If you can run to an reasonable voltmeter as well then with a bit of research on your part the other users will have a fair idea when something goes wrong.

 

Get a laminated card with the alternator's regulated voltage on it, its rated output, and the tail current you are happy to accept as indicating charged batteries.

 

Let it be known that:

 

1. The ammeter should be reading close to the alternator's rated output when revving immediately after first start of the day.

 

2. Just before the last shut-down of the day the voltmeter should be reading close to the regulated voltage with less than 10 amps flowing.

 

3. If the ammeter is not reading the stated tail current with no electrical things running the engine must be kept running above xxxx rpm until it does.

 

If 1. is not met in all probability there is a fault (faulty alternator or loose belt).

 

If 2 is not met the alternator is probably faulty (although a wiring connection may have gone resistive).

 

If 3 can not be met then there is probably a battery fault developing or the user needs to curb their electricity use.

 

You will probably have to slightly adjust the values to allow for the wiring of the particular boat.

 

 

Edited to add: The important thing for the OP is that the other users always get the batteries as fully charged as possible rather than discharge them too deeply. This assumes the battery bank capacity is more or less matched to "typical" electrical loads. It would not matter too much if one idiot ignored it because the next users would probably get things back and then have a say.

Edited January 22, 2016 by Tony Brooks

[cuthound]

Having had shares in boats for 22 years I am well aware how breathtakingly non-technical (stupid?) some people can be. An ammeter or amphour counting meter will be too complicated for some.

 

For this reason I would recommend a Smartgauge, along with a dymo label next to it saying recharge at 50% and keep charging until it has read 100% for at least one hour.

 

Edited to change of to or.

Edited January 22, 2016 by cuthound

[WotEver]

Tony's post meets the requirements cheaply.

 

Requires a bit more work but hardly rocket science.

 

Tony

[DHutch]

Is the plan to install the ammeter on the main battery cables to get the current in an our of the whole bank, or to install it in the alternator cable to confirm the alternator is outputting the correct current and hence power?

Do you any instrumentation at all at present? Voltmeter even? If so what type/spec/etc.

Surely on a share boat the simplest solution would be a Smartgauge, all crews can see easily if they need to charge or not. Plus the voltage indication on each bank gives a basic notion as to if the alternator/s are working. It's also a bit scary if a syndicate cant afford £180 to help maintain their boat.

I also agree that a simple to read 'state of charge' gauge is what is likely needed, although at the same time if they have managed without for years, an ammeter might well provide the information for the OP to resolve the issue and get back to where they where.

And given an ammeter is not a stupid thing to run alongside a smart gauge, the risk is low.

 

It will also help find if you have a stray draw, or leak, somewhere. Which would be another explanation.

 

That said, a set of batteries is what £120 ? Even three years is a lot less than we get from a set.

 

Would not be hard to cover the cost of a 'State of Charge' battery monitor of your choice with the saving.

Daniel

[Guest]

 

Well obviously. If I want to measure current in both directions, I'd buy an ammeter that had a centre zero. Even my missus thought of that!

Digital?

[WotEver]

Digital?

No, Loafer has a 'proper' boat

... given an ammeter is not a stupid thing to run alongside a smart gauge...

I hinted at that in post #2 but was wary of saying it out loud.

 

Tony

[ditchcrawler]

Having had shares in boats for 22 years I am well aware how breathtakingly non-technical (stupid?) some people can be. An ammeter or amphour counting meter will be too complicated for some.

 

For this reason I would recommend a Smartgauge, along with a dymo label next to it saying recharge at 50% and keep charging until it has read 100% for at least one hour.

 

Edited to change of to or.

I also had one for 8 years and would agree 100% with you and dont put it in the cupboard.

Having watched Ownerships in their day at Stockton the boats would moor half a mile from the marina lunchtime on Thursday, every thing on all night and Friday just tick over to the marina. Friday afternoon the next owner comes onboard, loads up and goes half a mile and sit there with the fridge and freezer going flat out. so 2 days hard work and no charge.

[Roger Crown]

If you can run to an reasonable voltmeter as well then with a bit of research on your part the other users will have a fair idea when something goes wrong.

 

Get a laminated card with the alternator's regulated voltage on it, its rated output, and the tail current you are happy to accept as indicating charged batteries.

 

Let it be known that:

 

1. The ammeter should be reading close to the alternator's rated output when revving immediately after first start of the day.

2. Just before the last shut-down of the day the voltmeter should be reading close to the regulated voltage with less than 10 amps flowing.

3. If the ammeter is not reading the stated tail current with no electrical things running the engine must be kept running above xxxx rpm until it does.

 

If 1. is not met in all probability there is a fault (faulty alternator or loose belt).

If 2 is not met the alternator is probably faulty (although a wiring connection may have gone resistive).

If 3 can not be met then there is probably a battery fault developing or the user needs to curb their electricity use.

 

You will probably have to slightly adjust the values to allow for the wiring of the particular boat.

 

Edited to add: The important thing for the OP is that the other users always get the batteries as fully charged as possible rather than discharge them too deeply. This assumes the battery bank capacity is more or less matched to "typical" electrical loads. It would not matter too much if one idiot ignored it because the next users would probably get things back and then have a say.

With all due respect Tony, most share boat people just want to enjoy their time on board for the short few weeks they get. Your instructions are straight forward and simple but some people will find them confusing and daunting. Not everyone has a leaning towards the technical. A simple device where one presses a button that shows that they should start charging at a certain level and stop at another level could not be simpler and almost stress free for all users.

[bottle]

Let's look at this from a different angle.

 

Share boat usually 8 shares but lets be pessimistic this one only has four shares, Smartgauge £160 (yes I know it can be bought cheaper)

 

£160 shared between four is £40 each, set of batteries £££

 

Is there no money in the 'emergency fund'

 

In the meantime check all connections are clean and tight.

 

As per cuthound:

 

 

For this reason I would recommend a Smartgauge, along with a dymo label next to it saying recharge at 50% and keep charging until it has read 100% for at least one hour.

[WotEver]

A simple device where one presses a button that shows that they should start charging at a certain level and stop at another level could not be simpler and almost stress free for all users.

In that case...

 

I would recommend a Smartgauge, along with a dymo label next to it saying recharge at 50% and keep charging until it has read 100% for at least one hour.

[bottle]

 

one presses a button that shows that they should start charging at a certain level and stop at another level could not be simpler

 

You do not even have to do that, the Smartgauge can be set up to display at all times.

 

Fit it in the saloon and they will not even have to get up from their seats. (tongue in cheek)

[ditchcrawler]

 

You do not even have to do that, the Smartgauge can be set up to display at all times.

 

Fit it in the saloon and they will not even have to get up from their seats. (tongue in cheek)

That or the galley, throw away the microwave and the under bed freezer.

O and the dishwasher.

[Roger Crown]

 

You do not even have to do that, the Smartgauge can be set up to display at all times.

 

Fit it in the saloon and they will not even have to get up from their seats. (tongue in cheek)

Oh no no, if going down that route then it has to be a BMV.

 

Coat

[Iain_S]

I also had one for 8 years and would agree 100% with you and dont put it in the cupboard.

Having watched Ownerships in their day at Stockton the boats would moor half a mile from the marina lunchtime on Thursday, every thing on all night and Friday just tick over to the marina. Friday afternoon the next owner comes onboard, loads up and goes half a mile and sit there with the fridge and freezer going flat out. so 2 days hard work and no charge.

 

That was our experience with Copperkins, exacerbated a fair bit by doing our own hoovering!

 

A Smartgauge fixed it.

[Graham.m]

I think this maybe a case where the only thing that stands a chance of solving the problem is a smartgauge.

 

But I would council the owners to look at recharge at 75% They won't but hopefully they will before the batteries get to 50%,

 

Also I would suggest that if at all possible when the boat comes in for change over that the shoreline is rigged and the batteries are put on charge with the biggest charger the batteries will stand.

 

This is the occasion where I wish the gauge could be set to read 0 SoC when the batteries are at 50%. It can be done with the BMV

 

Too many people cannot get their heads around only being able to take 50% of the energy out of a battery when it has 100% in it. They can empty the diesel tank so long as they get back, why not the battery attitude

Edited January 22, 2016 by Graham.m

[mickp]

After recent discusions im now proberly going to buy a( thing that shall not be named )sounds ideal to keep in the living room.,if theres nothing on the tv its somethink else to look at.it would be better for my better half to monitor also if im away from the boat a bit like water tank gauge which she does monitor

[DHutch]

But I would council the owners to look at recharge at 25% They won't but hopefully they will before the batteries get to 50%,

I presume you mean 25% DISCHARGE otherwise known as 75% state of charge? Rather than running the batteries down to 25% SoC?

 

 

Daniel

[Graham.m]

I presume you mean 25% DISCHARGE otherwise known as 75% state of charge? Rather than running the batteries down to 25% SoC?

 

 

Daniel

 

No Daniel I ,ean 75% SoC or put another way when the gauge say 75%

 

Been here with similar things people who not knowing will push the envelope down towards gauge reading 60/55/50% Say 50% and they will push below that, Oh it is not urgent we have a 50% in the battery

 

ED Brain working back wards

Edited January 22, 2016 by Graham.m

[WotEver]

I would council the owners to look at recharge at 25% They won't but hopefully they will before the batteries get to 50%

I am presuming that the 25% is a typo and Graham meant 75% SoC (25% DoD).

 

Tony

 

Edit - I see that Daniel types faster than me

 

No Daniel I ,ean 25% SoC

I fail to see how that makes sense? "They won't recharge at 25% but hopefully they'll do it before it reaches 50%"

 

??

 

Tony

Edited January 22, 2016 by WotEver