Charging of domestic batteries

[cereal tiller]

5 minutes ago, Dr Bob said:

Your current ammeter is obviously not measuring the current going into the domestic bank. You are nervous about disrupting stuff, so you current ammeter is not going to be much use. If you want to understand your boat electrics, you need a proper ammeter with a shunt installed on the negative of the domestic bank. The cheapest is the NASA one - and not difficult to fit. Order one now and fit it on the weekend so you then know what power is going in or out of your domestic bank.

Would rather have a Current Ammeter than an Obsolete one!

[MtB]

On 08/11/2017 at 21:45, WotEver said:

Oh no it isn’t! (Well, it is coming up to Panto season). There’s one for a fiver being discussed on another thread. Oh, plus three quid for a shunt. 

 

Have you tried out one of these? Do they tell you the direction of the current as well as measure the magnitude?

[WotEver]

6 minutes ago, Mike the Boilerman said:

 

Have you tried out one of these? Do they tell you the direction of the current as well as measure the magnitude?

They flash the decimal point to show discharge. Sorry, I got the price wrong, they’re seven quid. 

https://m.ebay.co.uk/itm/DC-100V-500A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/172733947168?_mwBanner=1

[Dr Bob]

Ok, a battery monitor then! Might as well be able to count amphrs out.

[WotEver]

Voltage, current, Wh, loads of stuff indicated. 

Sorry, I’m getting confused. It’s the 19 quid one that does all the counting stuff:

https://m.ebay.co.uk/itm/DC-120V-100A-Wireless-Volt-Ammeter-Power-Meter-battery-Charge-discharge-capacity-/182211747540?_mwBanner=1

The seven quid one only does bi-directional A & V

[MtB]

On 08/11/2017 at 22:01, WotEver said:

They flash the decimal point to show discharge. Sorry, I got the price wrong, they’re seven quid. 

https://m.ebay.co.uk/itm/DC-100V-500A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/172733947168?_mwBanner=1

 

I thought it might, having just had a look at mine. It has five wires sticking out of it, and came with no instructions!

To be fair though, ISTR there was a wiring diagram on the ebay listing.

[Dr Bob]

6 minutes ago, WotEver said:

They flash the decimal point to show discharge. Sorry, I got the price wrong, they’re seven quid. 

https://m.ebay.co.uk/itm/DC-100V-500A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/172733947168?_mwBanner=1

Tony, the delivery on this ammeter is 2 weeks! The upside of that is we can have 2 more weeks of posts to this thread!!! Get a Nasa one tomorrow and fit it Friday and put us all out of our misery.

[WotEver]

1 minute ago, Mike the Boilerman said:

 

I thought it might, having just had a look at mine. It has five wires sticking out of it, and came with no instructions!

To be fair though, ISTR there was a wiring diagram on the ebay listing.

Wiring diagram (looks like 3 of the wires all go to the same place):

 

[rowland al]

19 minutes ago, Dr Bob said:

Your current ammeter is obviously not measuring the current going into the domestic bank. You are nervous about disrupting stuff, so you current ammeter is not going to be much use. If you want to understand your boat electrics, you need a proper ammeter with a shunt installed on the negative of the domestic bank. The cheapest is the NASA one - and not difficult to fit. Order one now and fit it on the weekend so you then know what power is going in or out of your domestic bank.

Yes, you are right about that. 

However despite the crudeness off my current ammeter,  I'm surprised that when I temporarily connect the domestics to the starter battery it doesn't show a higher charging current even though the domestics are 50%. 

 

[WotEver]

Just now, Dr Bob said:

Tony, the delivery on this ammeter is 2 weeks!

Oh I doubt it would arrive that quickly from China but it might, I guess. OP has had his wiring for a considerable time, I can’t see him worrying about another few weeks

[MtB]

On 08/11/2017 at 22:09, rowland al said:

Yes, you are right about that. 

However despite the crudeness off my current ammeter,  I'm surprised that when I temporarily connect the domestics to the starter battery it doesn't show a higher charging current even though the domestics are 50%. 

 

 

That will be because they are still connected with their existing wiring, bypassing your bypass.

[MtB]

Or did you remove the positive post connector from the domestic bank first, then connect the positive post only with your jump lead?

[nicknorman]

37 minutes ago, Dr Bob said:

Your current ammeter

Tautology alert!

[Dr Bob]

7 minutes ago, Mike the Boilerman said:

 

That will be because they are still connected with their existing wiring, bypassing your bypass.

 

Just now, nicknorman said:

Tautology alert!

There is no raison why I wrote that

[MtB]

On 08/11/2017 at 22:21, Dr Bob said:

 

There is no raison why I wrote that

 

Are you raisin the steaks here, or what?

[Dr Bob]

8 minutes ago, Mike the Boilerman said:

 

That will be because they are still connected with their existing wiring, bypassing your bypass.

Am I being thick? The ammeter is likely to be located on the earth wire from the starter battery to earth, so just putting a jump lead across the 2 positives will not increase the current on the starter negative post to earth - so the amps are still the same. Of course we havent a clue where the ammeter is or how it is wired. Just get a battery monitor.

1 minute ago, Mike the Boilerman said:

 

Are you raisin the steaks here, or what?

Yes, defo prefer steaks to dried fruit.

[rowland al]

3 minutes ago, Mike the Boilerman said:

 

That will be because they are still connected with their existing wiring, bypassing your bypass.

When al the batteries are connected as one bank, surely the ammeter will 'see' it all as one battery. Ie no longer a distinction between the domestics or starter as far as the ammeter can 'see'. 

TBH, I'm beginning to realise I've come to the limit of my rookie electrical knowledge now and should accept I need to get someone to have a look and educate me, or read an idiots guide or something. 

[rowland al]

13 minutes ago, Mike the Boilerman said:

Or did you remove the positive post connector from the domestic bank first, then connect the positive post only with your jump lead?

I connected the positive of the starter battery to the positive of the leisure bank using the jumper then started the engine. I didn't remove any of the existing leads. All I was trying to do is create a single 12v bank.

 

[nicknorman]

7 minutes ago, rowland al said:

When al the batteries are connected as one bank, surely the ammeter will 'see' it all as one battery. Ie no longer a distinction between the domestics or starter as far as the ammeter can 'see'. 

TBH, I'm beginning to realise I've come to the limit of my rookie electrical knowledge now and should accept I need to get someone to have a look and educate me, or read an idiots guide or something. 

Did you just connect the positive terminals of the two battery banks together, or the negatives too?

[Dr Bob]

10 minutes ago, rowland al said:

When al the batteries are connected as one bank, surely the ammeter will 'see' it all as one battery. Ie no longer a distinction between the domestics or starter as far as the ammeter can 'see'. 

 

...but you said you only used one jump lead linking the 2 positives so they are not one bank.

If only the starter battery is connected then the current flows around a circuit from the alternator to the starter battery +ve then via the starter battery -ve to earth. The ammeter is on the -ve to earth wire (usually). If now you put a jump lead on, in addition to the flow round the starter battery, the current will also go to the domestic +ve and then via the domestic -ve to earth. This additional flow could be quite high if the SoC of the domestic is only 50% but your ammeter will not see that as it is only measuring current on the starter -ve to earth.

Did I mention....buy a battery monitor.

Edited November 8, 2017 by Dr Bob

[MtB]

On 08/11/2017 at 22:35, rowland al said:

I connected the positive of the starter battery to the positive of the leisure bank using the jumper then started the engine. I didn't remove any of the existing leads. All I was trying to do is create a single 12v bank.

 

 

Yes but you are still not getting it. You'd have to disconnect the positive post to force all the current to flow though the ammeter we suspect is measuring only the current to the engine battery.

[rowland al]

1 minute ago, nicknorman said:

Did you just connect the positive terminals of the two battery banks together, or the negatives too?

Initially I was going to do that with another jumper cable until I realised that the negatives from the starter and domestics were already connected together. Isn't that normal?

[nicknorman]

4 minutes ago, rowland al said:

Initially I was going to do that with another jumper cable until I realised that the negatives from the starter and domestics were already connected together. Isn't that normal?

Not necessarily, ours isn’t.

Another question- does the ammeter read zero in the middle and have a positive and negative range, or does it read zero at one end and thus only show current in one direction?

Edited November 8, 2017 by nicknorman

[Dr Bob]

25 minutes ago, rowland al said:

TBH, I'm beginning to realise I've come to the limit of my rookie electrical knowledge now and should accept I need to get someone to have a look and educate me, or read an idiots guide or something. 

The responses on this thread might be confusing as everyone is saying the same thing but in different ways. I see the problem as very simple.

- Your are charging your domestic bank ok, so  the alternator seems ok

- the amps showing up on your ammeter are not showing amps to the domestic bank

- If you want to measure amps to the domestic bank, which is a good thing to do to monitor the health of the batteries, then fit a battery monitor with V, A and Ahrs counter. They are not difficult to fit and can be obtained next day delivery.  A cheaper, simpler way may be to buy on of the clamp DC Amp meters as linked on the other thread but I have no idea how they work - again look at the other thread, but if you are interested in keeping batteries alive then you need a battery monitor ......or a Smartguage but that doesnt tell you amps.

You dont need to understand electrics to succeed here. When you get your battery monitor or SG, people here can help you understand what it is telling you and how to use it. Dont get put off.

Edited November 8, 2017 by Dr Bob
speeling agian

[rowland al]

1 minute ago, nicknorman said:

Not necessarily, ours isn’t.

Hmm..I've got to get away now guys. Thanks again for your thoughts. I need to get some more info and do a bit of reading. Any good stuff on the interweb? 

Obviously this isn't a big issue as the batteries do charge up fine. I'm just trying ti understand what I'm seeing and wondering whether the batteries are being charged up efficiently by the alternator, 

I'll try to get some pics in a few days I've learnt a few things but agree it's pointless trying to speculate much without accurate info from me, A decent meter would be good, so something I shall think about investing in.