Hymer s660 shunt

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Does anyone know where the shunt for the ammeter on the control panel lives?

It's a hymer s660. The ammeter has the needle stuck over to the right, I've contacted Schaudt who can supply me a new meter but I want to check/replace the shunt before installing a new meter and frying it.

Schaudt don't supply the shunt and the, very helpful, contact there says it's behind the main habitation switch but it's not there.

 

[Deleted member 13867]

If the shunt was faulty (it can only go open circuit) your 12 volt electrics would not work because the meter would be passing all the current and as it is quite a high internal resistance not enough current would flow. You could take the meter out and measure the voltage across its terminals this would be extremely low 75 millivolts at full rated shunt current so if it is a 20Amp shunt it would take 20 amps passing through it to develop a potential of 75 millivolts across it.
Good Luck
Dave

 

[crosscut]

Ok, thanks, I'll check that out.

Cheers

 

[Deleted member 967]

I have the same problem on my Hymer S700 1992.

I was having problems with very dim habitation lights and the water heater began to fail intermittently (gas shut off because of low voltage). I suspected an earth problem, but on checking I was getting 8.5v on both sides of the fuses in the block, even with all the fuses removed even though the battery was showing 14+v on hookup. I also had the amp meter going full deflection. I took the fuse out for the (amp meter accessories) fuse f6 and this brought the amp meter back to zero. I ran a separate wire fused at both ends direct from the battery + to the point above the cooker where there was a spare spade terminal behind the panel. All my lights began to be bright again and there is now battery voltage on one side of the fuses and 8.5v on the other. I assume this is coming from the shunt which is shown on the wiring diagram as between fuses f6 and f7 which both go to the amp meter. I am now running without fuse f6 in place and everything is working apart from the amp meter.

I thought the shunt must be behind the panel where the big red switch is by the fuse box to the left of the drivers seat. I have not been able to get behind there to look and was going to leave it to a professional when we return to the UK after the winter tour of Spain.

Can anyone can help both of us to locate the shunt?

When I had a Waeco B2B fitted 2 years ago the amp meter would show discharge instead of charge, the professional who fitted it assured me that there would be no problem and that the leisure batteries were being charged OK. (Clip on amp meter proved this) I have had other problems associated with this B2B and now doubt the professions opinion.

 

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Hi John

I think we may have different problems, It sounds like your shunt has gone open circuit and is therefore trying to pass all the current though the ammeter.
Hence your ammeter showing high current use by pinning to the right and there being a reduced current flow to the van.

My current flow to the van is normal so as Dave has pointed out the shunt must be intact, or as I type it occurs to me that ..... someone has performed the same modification to bypass the shunt before I bought the van.

I'll test the flow to the ammeter, when I have daylight and opportunity, as Dave has suggested. I have pulled out the fuse box and I can't see a shunt anywhere on it, the back of the red switch doesn't have anything other than the two main supply wires attached (and doesn't look disturbed since it was made)

Further investigation is required.
I'll keep you posted on any developments. If you locate the shunt let me know.

Alex

 

[Deleted member 967]

The shunt is located on the back of the fuse box/ relay panel, just below the red key (very small coil of thick, uninsulated wire). You do have to be very careful pulling it forward as it's very easy to short it out on the metal surround, so if you are going to remove it you need to disconnect all batteries. The same fault can sometimes be caused by the jumper connection (brass strip) connecting the top several few fuses together being cracked.

So now we know where it is

John

 

[crosscut]

Right, I've found mine, I guess it's the original.
I have taken some pictures.
It appears to be fine on mine, It measures a resistance of 0.3ohms.

I have no idea why my ammeter would have gone wrong.


It is the brass loop in the centre of the picture.

Here are couple of shots from further back to put it in context.




It's not too hard to get at.
There were no screws on the front of my fuse box (or a fuse box lid if anyone knows where I might get one?)
The fuse box pulls out with some wiggling and there is enough slack on the wiring to get it out and twist it to see what is going on.
It is a good idea to disconnect the batteries as it would be easy to short them out in the process.

I'm just waiting for my replacement ammeter, before I fit it I'm going to do a thorough check of the circuit board and all the connections before wiring it in and firing it up.

Fingers crossed, I'll let you know.

 

[crosscut]

I have the same problem on my Hymer S700 1992.

I was having problems with very dim habitation lights and the water heater began to fail intermittently (gas shut off because of low voltage). I suspected an earth problem, but on checking I was getting 8.5v on both sides of the fuses in the block, even with all the fuses removed even though the battery was showing 14+v on hookup. I also had the amp meter going full deflection. I took the fuse out for the (amp meter accessories) fuse f6 and this brought the amp meter back to zero. I ran a separate wire fused at both ends direct from the battery + to the point above the cooker where there was a spare spade terminal behind the panel. All my lights began to be bright again and there is now battery voltage on one side of the fuses and 8.5v on the other. I assume this is coming from the shunt which is shown on the wiring diagram as between fuses f6 and f7 which both go to the amp meter. I am now running without fuse f6 in place and everything is working apart from the amp meter.

I thought the shunt must be behind the panel where the big red switch is by the fuse box to the left of the drivers seat. I have not been able to get behind there to look and was going to leave it to a professional when we return to the UK after the winter tour of Spain.

Can anyone can help both of us to locate the shunt?

When I had a Waeco B2B fitted 2 years ago the amp meter would show discharge instead of charge, the professional who fitted it assured me that there would be no problem and that the leisure batteries were being charged OK. (Clip on amp meter proved this) I have had other problems associated with this B2B and now doubt the professions opinion.

I don't know about the Waeco, but if you run a piece of wire in place of the shunt ( the easy way would be to connect the fuse terminals of 6 and 7 together on the right hand (battery) side of the fuse box (there are screw terminals so it would be an easy bodge), you could do away with the long wire from the battery to the control panel as a temp fix. It would mean the ammeter just wouldn't show charge or drain but the electrics should work as normal.

 

[harrow]

Right, I've found mine, I guess it's the original.
I have taken some pictures.
It appears to be fine on mine, It measures a resistance of 0.3ohms.

I have no idea why my ammeter would have gone wrong.

View attachment 18809
It is the brass loop in the centre of the picture.

Here are couple of shots from further back to put it in context.
View attachment 18810

View attachment 18811

It's not too hard to get at.
There were no screws on the front of my fuse box (or a fuse box lid if anyone knows where I might get one?)
The fuse box pulls out with some wiggling and there is enough slack on the wiring to get it out and twist it to see what is going on.
It is a good idea to disconnect the batteries as it would be easy to short them out in the process.

I'm just waiting for my replacement ammeter, before I fit it I'm going to do a thorough check of the circuit board and all the connections before wiring it in and firing it up.

Fingers crossed, I'll let you know.

I think you will find that your ammeter is really a voltmeter!
Now if things seem to be reasonably powered then the shunt is not open circuit, stay with me..
But if the shunt develops more resistance (dirty connections etc) then the "meter" will have a higher reading.
The simple maths is V=IxR
if you increase R the resistance then the meter will read higher.
I accept cash in a plain brown envelope...haha

So disconnect the batteries, clean up the connections and I think you will be fine.

 

[crosscut]

I think you will find that your ammeter is really a voltmeter!
Now if things seem to be reasonably powered then the shunt is not open circuit, stay with me..
But if the shunt develops more resistance (dirty connections etc) then the "meter" will have a higher reading.
The simple maths is V=IxR
if you increase R the resistance then the meter will read higher.
I accept cash in a plain brown envelope...haha

So disconnect the batteries, clean up the connections and I think you will be fine.

I wouldn't have thought that a slight increase in resistance would cause the meter to break. When disconnected from the wiring altogether the needle is stuck over to the right. It should definitely rest in the centre of the dial. Even when I removed the glass to physically return the needle to the centre it stayed stuck to the right.

I also was advised to try connecting a 1.5v battery across the contacts which can restore the meter to function, this had no effect.

I have a new meter on order so when it arrives I will test the millivolts going to it before I connect it. This should read 75 millivolts for 20amps current according to Dr Dave so that will tell me if the circuit is working correctly.

I will try cleaning the contacts too, that's an ongoing job anyway and has bought all the tank level meters back to life so it's worth doing.

 

[harrow]

I don't know the meter mechanism was physically damaged, yes as you say check the voltage developed between the points that the meter connects to, you don't want to ruin the new one.

It is a very old fashioned idea to have all that cable routing down to that panel and then back through the van again.

As vehicles swapped over to alternators and potential current levels went up cars started using voltmeters but I can understand the comfort factor of virtual ammeter set up.

I use digital voltmeters for some things but on occasions an analogue meter does a better job.

 

[crosscut]

I don't know the meter mechanism was physically damaged, yes as you say check the voltage developed between the points that the meter connects to, you don't want to ruin the new one.

It is a very old fashioned idea to have all that cable routing down to that panel and then back through the van again.

As vehicles swapped over to alternators and potential current levels went up cars started using voltmeters but I can understand the comfort factor of virtual ammeter set up.

I use digital voltmeters for some things but on occasions an analogue meter does a better job.

Haha Yes it's a pretty inefficient setup.

I do quite like the simplicity of these old vans, partly because I can fix them and partly because they are usually very reliable and functional. It also really bugs me when modern stuff breaks down and you have to throw the whole thing away and replace it. My day job is being a recording engineer I also do the maintenance on the studio, after about 1990 things started getting really fiddly and corners were really cut for cost so those are the units that get thrown away even though they cost a fortune to buy in the first place. The older stuff just keeps going and when it goes wrong you can usually find a way to get it running again.
I regularly go out gigging with a 60 year old guitar amp (about once or twice a week) a new one would never take 60 years of that.
The same goes for motorhomes and cars etc....
It's hard to imagine a modern motorhome still going strong in 25 years with only minor easily rectified faults.

Having said that I may get a cheap digital shunt meter to tell me what is really going on too...... I've seen them for about £4 on ebay.

 

[Deleted member 13867]

You could always replace both the shunt and the ammeter with something like this. so you get both the current and voltage for around £7.00
DC 4.5-30V 0-50A LED Digital Voltmeter Ammeter Voltage AMP+Current Sensor Shunt | eBay
Dave

 

[Deleted member 967]

Hi John

I think we may have different problems, It sounds like your shunt has gone open circuit and is therefore trying to pass all the current though the ammeter.
Hence your ammeter showing high current use by pinning to the right and there being a reduced current flow to the van.

My current flow to the van is normal so as Dave has pointed out the shunt must be intact, or as I type it occurs to me that ..... someone has performed the same modification to bypass the shunt before I bought the van.

I'll test the flow to the ammeter, when I have daylight and opportunity, as Dave has suggested. I have pulled out the fuse box and I can't see a shunt anywhere on it, the back of the red switch doesn't have anything other than the two main supply wires attached (and doesn't look disturbed since it was made)

Further investigation is required.
I'll keep you posted on any developments. If you locate the shunt let me know.

Alex

Hi Alex and Dave.

Can you clear something up in my mind?

Today I reconnected the fuse f6 and when I was on mains hook up. The amp meter deflected fully to the right (charge) When I turned off the charger the meter deflected fully to the left (discharge).

!. So the charger is working OK. I also have solar and a separate meter reading the voltage of the batteries. The solar meter is showing the voltage of the leisure battery rising with the mains charge. I only appear to be getting 5 amps out of the charger at the leisure batteries on the clip on meter. The charger is putting 14.5v out. With the solar connected the clip on meter is pulsing with the solar disconnected it is steady at 5 amps. The solar output is currently 0.88 amps

I am not sure how this setup is working? If you put a shunt against a wire (such as in the clip on meter) a current is developed in the shunt that powers the meter. ( ie .25 amp flow 75ma flow to the meter as previously explained)

However this setup seems to be a bit of bare wire between two terminals f6 and f7. That to me, should result in a short circuit. Both f6 and f7 are connected to the amp meter? and according to the diagram the shunt is across both of these points with power coming from the main switch. to f6.

So has the shunt broken/cracked (open circuit)? or has it gone high resistance? How is this allowing the full voltage to flow to the amp meter?

Alex Is the shunt a plug in device as it seems to be shown on the diagram as a flat plug connector for fuses f6, f7 and f8
Iit would seem that someone has been at your fuse box before you. Mine is held in with 4 long screws. It was hard to pull out and there seems to be no slack wire to allow it to come right out, to even see into the back as in your photos.

 

[Deleted member 13867]

Just a quick reply for the moment.
This can only be generic as i don't know your actual setup.
The basic diagram of a shunt type installation is attached this will read all the charge / discharge to and from the leisure batteries IE: all the sources of charge flow through the shunt (alternator charging is left off but could be added as the others) any current flowing through the shunt will cause a VERY small voltage drop typically at maximum current flow, a 50 Amp shunt will develop 75 millivolts across it this would be calibrated to make the meter read 50 Amps even though it is actually a 75 millivolt full scale deflection meter. As you need to know charge and discharge a centre zero meter will be fitted and this will read Full scale deflection at either - 75 millivolts or +75 millivolts depending on the direction of current flow through the shunt. Please note the resistance of the shunt is very low perhaps 0.0015 Ohm so this would appear to be short circuit on a normal test meter. If the resistance were higher heat and excessive voltage drop would be developed which would cause problems to the 12 Volt equipment in the 'van.
Oh just a thought if the connections to the shunt have a high resistance (dirty contacts) this would have the effect of increasing the voltage drop and making the ammeter read high possibly at full scale.
Hope this helps i will have more time later for perhaps a better explanation.

 

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John,

The symptoms you describe are very much like the shunt has gone open circuit. This means the whole supply (and charge) is being sent thought the meter, which can't cope and is therefore sending the needle to full deflection and not letting the full charge through to the rest of the van (or when charging through to the battery)

I suspect this is what has happened to mine in the past (there has certainly been someone in there before me) and the shunt replaced with a short length of copper wire soldered on to some ring connectors. Which will enable the system to work exactly as normal but with (probably) nothing or very little showing on the "strom" meter.

I expect my meter was damaged in the incident before the wire to replace the shunt was fitted and the needle therefore stuck over to the right.

I have just measured my "jumper" and there is no measurable resistance so i need a replacement shunt. Any ideas? I know that Hymer aren't cheap, there must be a reasonably priced alternative?

This for example

20A DC CURRENT SHUNT RESISTOR for DIGITAL & ANALOG GAUGE AMP METER AMMETER SUV | eBay

Though I would feel better about this...

80amp shunt for 50mV ammeter gauges 24681 | eBay

I just need to work out the correct rating.

Of course it's possible that the wire "jumper" is calibrated to work as a shunt, happily I won't be risking any damage to the meter by testing it in situ.
If I get no readings that are useful then I will need a shunt, if I get badly calibrated readings then I'll be reasonably happy.

 

[Burtie]

I had loads of trouble on my s750 some days the lights on the meters would be dull sometimes they would work ok I'm pretty sure the last owner messed about with all the wiring in mine so I stripped it all out ready to replace with a unit that I can understand but I still have all the bits that I've taken out

 

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I had loads of trouble on my s750 some days the lights on the meters would be dull sometimes they would work ok I'm pretty sure the last owner messed about with all the wiring in mine so I stripped it all out ready to replace with a unit that I can understand but I still have all the bits that I've taken out

I think the whole system needs either replacement or refurbishment when they get to that age, 25 years of electronics sitting in the extractor unit above the cooker doesn't leave reliable spade connectors. I have stripped mine out and cleaned all the contacts. The switches are still a bit hit and miss.

If you are getting rid of your old bits then I could do with a shunt and a fuse box cover, probably some other bits would come in handy too. Those S750s are pretty special, have you had it long?

 

[Burtie]

I think the whole system needs either replacement or refurbishment when they get to that age, 25 years of electronics sitting in the extractor unit above the cooker doesn't leave reliable spade connectors. I have stripped mine out and cleaned all the contacts. The switches are still a bit hit and miss.

If you are getting rid of your old bits then I could do with a shunt and a fuse box cover, probably some other bits would come in handy too. Those S750s are pretty special, have you had it long?

I've had it a couple of years now I'm still in the process of renovating it updating it with electrics and 12 volt I've already put a new floor in next is putting the LPG tank and the petrol eberspacher I will try to get in this weekend and see if I can hunt the bits out and let you know what I have

 

[crosscut]

So finally an update.

I replaced the meter with the new one after pulling the shunt out and covering it in heatshrink to prevent possible shorts when removing the fuse box.

It appeared to be just a bit of fat copper wire, when measured out of the circuit with the contacts all cleaned up there was no apparent resistance, understand the spec for original was 0.003ohm (or was it 0.03?) I wouldn't have expected to be able to measure with my meter.

So I installed the new meter safe in the knowledge that the worst that would happen is it wouldn't show me anything, I wasn't going to fry it by passing all the habitation power through it.

It worked, seems to be showing what I would expect, the biggest surprise being the current draw of the regular bulbs in the lamps..... suffice to say I have ordered some replacement LED bulbs.

So now everything seems to be working as intended apart from the fridge, now removed (that was a puzzle) and being diagnosed.
Looks like the 240v element is gone. and the gas just full of rust.
If only the label with the model number hadn't been rendered illegible with 25 years of cleaning I could get some parts easily..... as it is detective work is in order.