Battery voltage drop to appliances

[Marcus and Jude]

Hi, Our Bailey Adamo has had this problem since we bought it 2 years ago and we have not been able to find anyone to fix it yet! There is a voltage drop from the Battery to the Appliances of 1.5 to 2.5v - tested by two MOHO mechanics, but they don't know why! We mainly use the battery to watch TV which draws 2.3amp and with a 90amp battery it should last about 15 hours but only lasts for 5 to 6 before switching over the to vehicle battery and running it down. Also, the fridge and heater will not work from the leisure battery (not that we would normally do this as we use EHU or Gas for these, but it should which might be part of the problem?). We believe the issue is with an electrical component between the battery and the appliances but no one has been able to tell us which one this might be. It has been suggested the BCM might be at fault but not being electrically minded and I understand this has more than one function I haven't a clue how to proceed. Would anyone on this forum be able to help please?

 

[GeoffnDee]

On your Bailey Motorhome I would not expect the fridge or the heater to work on 12v ,( except for their controls) and the fridge should only cool on 12v with the engine running (using power from the starter battery). The BCA Power control unit is switching to the starter battery to save the leisure battery from being dis-charged to low (which would damage it).
Has the leisure battery been tested as it may not be holding enough charge and have all of the earth connections been checked along with the main battery connections to the Power control unit ?
If you do need the Power control tested/repaired www.apuljackelectronics.co.uk should be able to help. (your unit will be shown in the BCA section of their catalogue) .
There should also be a battery current monitor fitted that is linked to the Power control and the leisure battery , Bailey may be able to help with its location.

 

[Ingwe]

You say that the leisure battery is 90Ah and that watching TV should be possible for 15 hours but is lasting only 5-6 hours. This assumes that the battery is fully charged and there is no other drainage of current.

In our older Bailey, we had a 90Ah leisure battery and on our first trip to Spain in January 2016, we kept getting a message on the TV that the leisure battery was too low and we would turn off the TV. The problem was we weren’t putting enough charge back into the battery by driving or the one 120w solar panel, given how overcast it was.

Our fridge only ever works on 12v when the engine’s running and, in this mode, acts only to keep stuff cool and won’t freeze anything.

 

[fred_jb]

For there to be a voltage drop there has to be current flowing and a resistance in the path of the current for that voltage to be dropped across. Does the battery voltage read normally at the same time that the voltages at appliances show a drop?

If so, and if you can locate the first point in the wiring where the voltage drop appears, then the problem could be between that point and the battery. It might be as simple as a loose connection or poorly crimped cable.

Alternatively if the voltage at the battery drops as soon as an appliance is turned on, then it could just be a dying battery which is no longer meeting its original capacity spec and has developed a high internal resistance. Maybe you could take it to Halfords for a free battery test. They use a gadget which can give a good indication of battery health.

 

[Lenny HB]

Maybe you could take it to Halfords for a free battery test. They use a gadget which can give a good indication of battery health.

Useless for leisure battery test it will be a CCA test.

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[AdrianChen]

Hi, Our Bailey Adamo has had this problem since we bought it 2 years ago and we have not been able to find anyone to fix it yet! There is a voltage drop from the Battery to the Appliances of 1.5 to 2.5v - tested by two MOHO mechanics, but they don't know why! We mainly use the battery to watch TV which draws 2.3amp and with a 90amp battery it should last about 15 hours but only lasts for 5 to 6 before switching over the to vehicle battery and running it down. Also, the fridge and heater will not work from the leisure battery (not that we would normally do this as we use EHU or Gas for these, but it should which might be part of the problem?). We believe the issue is with an electrical component between the battery and the appliances but no one has been able to tell us which one this might be. It has been suggested the BCM might be at fault but not being electrically minded and I understand this has more than one function I haven't a clue how to proceed. Would anyone on this forum be able to help please?

How old is the battery?

If the battery voltage measured at the battery terminals is higher than what is measured at the device end of the cable then there is some drop caused by fuses, or connections in that cable run. 3% drop considered OK for critical items, but shouldn't be a whole lot more for anything on its own.

If the battery voltage drops very low/quickly when a load is applied (and the voltage is similar at the terminals at each end of the cable) then the battery is either in a low state of charge, or possibly knackered, and needs a proper capacity check/replacement.

 

[peterc10]

Voltage drops like that usually means that the wiring is too thin

 

[fred_jb]

Useless for leisure battery test it will be a CCA test.

I went with my son to get the battery in his newly acquired car tested as although it was starting OK the car was frequently complaining about low voltage after being parked.The car supermarket place he had bought the car from were happy to pay for a replacement battery if the printout from the Halfords test indicated it was in poor condition. I could be wrong, but from what I remember the test was a bit more sophisticated than simply CCA rating, and the printout showed several different parameters.

 

[mitzimad]

I went with my son to get the battery in his newly acquired car tested as although it was starting OK the car was frequently complaining about low voltage after being parked.The car supermarket place he had bought the car from were happy to pay for a replacement battery if the printout from the Halfords test indicated it was in poor condition. I could be wrong, but from what I remember the test was a bit more sophisticated than simply CCA rating, and the printout showed several different parameters.

yes they can test the starter battery but leisure batteries are different in that they release energy slowly only way to test a leisure battery is to put a known load on it for a long period of time

 

[Lenny HB]

I went with my son to get the battery in his newly acquired car tested as although it was starting OK the car was frequently complaining about low voltage after being parked.The car supermarket place he had bought the car from were happy to pay for a replacement battery if the printout from the Halfords test indicated it was in poor condition. I could be wrong, but from what I remember the test was a bit more sophisticated than simply CCA rating, and the printout showed several different parameters.

Still not suitable for a leisure battery.

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[autorouter]

There is a voltage drop from the Battery to the Appliances of 1.5 to 2.5v - tested by two MOHO mechanics, but they don't know why!

If those two motorhome mechanics can't find the fault, then you need an auto electrician. This is standard fault-finding stuff for an electrician. Basically the voltage drop must be across a resistance. If for example the battery voltage is 12.5V and at the same time the voltage across the appliance is 10.5V, then there must be an extra resistance somewhere along the supply wires.

I would test first to see if the drop was along the positive feed or the negative return. Then I would go along the offending wire, testing each joint and connection, until I found where the drop is. I would suspect every possible connection and fuse, until I found the fault. If it's not a fuse or connection, then the fault may be a break in the wire inside the insulation. It's there somewhere, it just needs to be found.

For comparison, the wiring is designed so that the maximum voltage drop between the battery and the appliance is 3% or less, which means it should be less than 0.36V.

 

[Raul]

If those two motorhome mechanics can't find the fault, then you need an auto electrician. This is standard fault-finding stuff for an electrician. Basically the voltage drop must be across a resistance. If for example the battery voltage is 12.5V and at the same time the voltage across the appliance is 10.5V, then there must be an extra resistance somewhere along the supply wires.

I would test first to see if the drop was along the positive feed or the negative return. Then I would go along the offending wire, testing each joint and connection, until I found where the drop is. I would suspect every possible connection and fuse, until I found the fault. If it's not a fuse or connection, then the fault may be a break in the wire inside the insulation. It's there somewhere, it just needs to be found.

For comparison, the wiring is designed so that the maximum voltage drop between the battery and the appliance is 3% or less, which means it should be less than 0.36V.

There is no such thing of volt drop on positive or negative, the voltage will only be present between the -ve and +ve. You get no voltage (potential) on one side of a circuit, without the other, as you have no reference.
And negative is never the return in DC, the positive is. The DC flowing trough copper, is always from source to load from negative, because: a atom of copper, aluminium and all other electrically conductive metals, has one free negative electron in their atom, that's attracted to the positive side. Hence when a load closes a circuit, the chain reaction starts and the free negative electron is on the move towards the positive side. And then you have a current flow that you can measure.

When you charge, the charger is the source, and the battery is the load so current flows into the battery negative. Hence shunt on negative.
In the OP case, to test effectively with success, you have to remove all negative paths from source, and add one at the time to detect when the current flows and where. A highly skilled auto electrician wont be hanging around motorhomes, you will get standard hit and miss basic and intermediate circuit troubleshooter. Very time consuming and not much of a reward.

 

[Marcus and Jude]

Thank you all for your input and help. It has given me much food for thought. To that end it seems I need a professional Auto Electrician to resolve this issue. Apuljack Electrics are based in North Somerset, I live in Poole/Bournemouth, can anyone recommend an electrician in my area please?

 

[headlight]

Thank you all for your input and help. It has given me much food for thought. To that end it seems I need a professional Auto Electrician to resolve this issue. Apuljack Electrics are based in North Somerset, I live in Poole/Bournemouth, can anyone recommend an electrician in my area please?

Was the motorhome new when you bought it 2 years ago ie the leisure battery is 2 years old ?

 

[bigtwin]

Thank you all for your input and help. It has given me much food for thought. To that end it seems I need a professional Auto Electrician to resolve this issue. Apuljack Electrics are based in North Somerset, I live in Poole/Bournemouth, can anyone recommend an electrician in my area please?

Apuljack are engineers not your average ‘Auto Electrician’. They specialise in all of the electronics stuff.

You need to find someone who can systematically trace the wiring and fault find along the way.
I suggest, given your location, that you try a marina.

Ian

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[GeoffnDee]

www.essanjay.co.uk in Poole may be able to help or recommend a local auto electrician

 

[Ian_H]

There is no such thing of volt drop on positive or negative, the voltage will only be present between the -ve and +ve. You get no voltage (potential) on one side of a circuit, without the other, as you have no reference.

I think what autorouter was suggesting was putting a voltmeter across the length of eg the positive cable while under power, when you will see the voltage drop across the cable.

 

[autorouter]

The circuit I refer to is from the battery positive terminal, along the positive wire, through the appliance and back through the negative wire to the negative battery terminal. If there is absolutely zero resistance in those wires, the voltage measured across the appliance will be exactly the same as the voltage measured across the battery terminals.

However the wires will always have some resistance, so the appliance voltage will always be a bit lower than the battery terminal voltage. Typically this will be designed to be lower than 3%, which is 0.36V for a nominal 12V circuit.

Usually in a vehicle, the negative return is through the chassis, which is substantial metal, so even though it is steel, it has a very low total resistance. So usually the voltage drop along the negative return path can be assumed to be very low. However it is certainly possible for a resistance to develop at one of the negative connections. It's just more probable that the resistance will be in the positive side, because that could have a busbar, fuse, switch, relay etc, and all the connections to those items.

We know that the voltage measured across the appliance terminals in this case is a couple of volts lower than the voltage measured across the battery terminals. What I was suggesting is that the first thing to establish is whether the voltage drop is on the positive side, or the negative side.

You could, for example, measure the voltage between the positive terminal of the battery and the positive terminal of the appliance. That is zero in theory, and less than 0.18V by design. If it's more than that, further investigation of the positive wire is needed.

You could also measure the voltage between the negative terminal of the battery and the negative terminal of the appliance. That is zero in theory, and less than 0.18V by design. If it's more than that, then further investigation of the negative current path is needed.

But at least you will know which of the wires is the problem. Of course you need to ensure the appliance is switched on, and drawing its usual current in amps. Otherwise there will be no current flow, no amps and therefore no voltage drops across any resistances.

 

[Marcus and Jude]

www.essanjay.co.uk in Poole may be able to help or recommend a local auto electrician

Thank you. They are lovely people and have done other for me as well as looking at this issue, but they no longer have an auto electrical specialist available and so were not able to help further.

 

[Marcus and Jude]

Was the motorhome new when you bought it 2 years ago ie the leisure battery is 2 years old ?

It’s not the battery.

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[Raul]

I think what autorouter was suggesting was putting a voltmeter across the length of eg the positive cable while under power, when you will see the voltage drop across the cable.

You can't have a voltage drop across a cable, but a across a circuit. First you measure at source, ( battery end) then you move to the load end and see the drop across the circuit.
If there is a drop, you can test for resistance and continuity on each leg ( split open) of the circuit. Weaker leg will tell you weather is the culprit, that if one reads good. If both reads low, could be just undersized conductors. For that you need a cross-section resistance table for each meter, and know the load requirement. In layman's the tester needs to have good knowledge of tracing a bad connection, or a undersized wire. Ppl often add on things, or could simply be a bad negative.

 

[Raul]

You could, for example, measure the voltage between the positive terminal of the battery and the positive terminal of the appliance. That is zero in theory, and less than 0.18V by design. If it's more than that, further investigation of the positive wire is needed.

Yes, you can do that with an additional cable and compare each path, take a cable from source to the load and measure across that cable and existing -ve, then repeat that on the +ve.
What happens if both give low readings? Or voltage drop still there?

 

[headlight]

It’s not the battery.

In your opening post you stated that you are only getting 5-6 hours at a 2.3 amp draw so 12-13 amps drawn before low voltage warning ?

 

[autorouter]

You can't have a voltage drop across a cable, but a across a circuit.

It's usually hard to measure the voltage drop across a length of cable - for example from the consumer unit in the hallway to the toaster in the kitchen. But in principle you could actually measure it. In a motorhome things are a lot closer together, so it is often quite possible to measure the voltage drop along the cable from the battery to the appliance.

The resistances causing the voltage drop are usually at the connectors of the wire, rather than along the whole length of the cable. Especially if the circuit worked fine to start with, but has developed a fault. If it's always had the fault, then worth looking at the possibility of undersized cable.

 

[Ian_H]

In a motorhome things are a lot closer together, so it is often quite possible to measure the voltage drop along the cable from the battery to the appliance.

I did this after having solar/lithium fitted, in an attempt to get the installer to accept he should have increased cable size from battery to DS300 distribution box.

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[Spriddler]

In a motorhome things are a lot closer together, so it is often quite possible to measure the voltage drop along the cable from the battery to the appliance.

I extend one of my test meter probes with a length of wire with croc clips on the end. The voltage drop caused by the extension wire is minimal but can be measured by comparing the voltage reading on the meter by measuring the voltage at the battery terminals with and without the extension wire.

 

[Marcus and Jude]

In your opening post you stated that you are only getting 5-6 hours at a 2.3 amp draw so 12-13 amps drawn before low voltage warning ?

We believe this is due to the fault as we should be getting 50% of an AGM battery i.e. 45amps before it shows 11.7 volts on the control panel and then switches to the vehicle battery.

 

[Marcus and Jude]

We believe this is due to the fault as we should be getting 50% of an AGM battery i.e. 45amps before it shows 11.7 volts on the control panel and then switches to the vehicle battery.

I should have added the battery is brand new.

 

[Ian_H]

A

We believe this is due to the fault as we should be getting 50% of an AGM battery i.e. 45amps before it shows 11.7 volts on the control panel and then switches to the vehicle battery.

Sounds like there may be other users taking power. Can you use a clamp meter to measure the current flowing at the battery and at the appliance end? If not the same, you need to find where else it is going. If it is the same, its a cabling/connector fault or the cable is too thin.

 

[fred_jb]

Do you know where the control circuit connects in order to monitor the leisure battery voltage? If it connects directly to the battery terminal and therefore gets a true reading, then the battery really is down to 11.7V which would indicate either a poor battery or some heavy drain you are not aware of running it down more quickly than expected. To eliminate this possibility you need to measure the current coming from the battery and see if it equates to whatever you have switched on and if it goes down to near zero with everything switched off.

If the control panel is reporting the battery is down to 11.7V and causing a switchover to the starter battery, but the leisure battery actually measures significantly more than 11.7V with a multimeter directly across its terminals, then the control circuit is getting a misleadingly low reading, possibly due to the same issue causing the voltage drop at appliances. It all depends on where the control panel is measuring the voltage.

Have you checked that the battery has a good ground connection? Try measuring the resistance from battery negative to somewhere on the vehicle chassis/bodywork. It should be near zero.