Battery trip problem developed

[afarr86]

Hi,

My camper has a new 12v battery and I have wired up a split charge relay with a 100 amp blade fuse near van battery and a 100 amp blade fuse after the split charge relay that joins to a pair of 110 amp hour 12 volt leisure batteries wired in parallel. However, between the blade fuse nearest the van battery and the split charge relay I also connected a 50 amp trip so I could quickly isolate the van battery from the 12 volt system. The split charge relay was working - clicking on a certain voltage and charging the leisure batteries

Started wiring up a few things through a 12v fuse box - 12 volt led lights and panel with USB and cigarette sockets, and these worked fine. Today when I started van after about a minute when the split charge relay was about to kick in the 50 amp trip "trips". What could be causing this after it was working please?

 

[OnlQQker]

Have you got a smart alternator?
Are the leisure batteries grounded to the chassis?

This vid might help

 

[Lucien Nunes]

when the split charge relay was about to kick in the 50 amp trip "trips"

By 'trip' I take it you mean circuit breaker? What type of circuit breaker is it? Why did you choose 50A rating?

If the breaker is wired in series with the relay contacts, then unless the wiring is damaged and shorted to the chassis, the relay must have been closed at the moment it tripped. Quite possibly, it was a legitimate trip because the charging current was well over 50A. If you had started drawing current from the leisure battery with your lighting etc, its voltage would have dropped somewhat, but the vehicle battery was in a good state of charge with the alternator pushing its voltage up. At the moment of relay closure there can be a short period of very high charging current while the voltages of the leisure and vehicle batteries equalise. This might not have happened previously when testing the split charging, because the leisure battery had been more fully charged before you had installed the fuse box and started taking current from it.

Check the voltages of the two batteries (can be done at the two sides of the relay contacts) just before starting, then once the relay closes watch the leisure battery voltage and if it climbs towards the alternator voltage but the circuit breaker still trips, it's probably just too small for the combination of large leisure batt capacity in good condition and the available charging current. If either side of the system shows an abnormally low voltage, then further investigation is needed for faults.

If the breaker trips when cranking the engine, it means the relay is not opening when the alternator stops and some of the cranking current is being drawn from the leisure battery. This can be a problem with straight voltage sensing relays that are not interlocked with the alternator charge warning. Any delay in opening after stopping the engine due to high battery terminal voltage that allows even a second of cranking on the leisure battery during a restart, gives an opportunity for the breaker to trip.

 

[afarr86]

By 'trip' I take it you mean circuit breaker? What type of circuit breaker is it? Why did you choose 50A rating?

If the breaker is wired in series with the relay contacts, then unless the wiring is damaged and shorted to the chassis, the relay must have been closed at the moment it tripped. Quite possibly, it was a legitimate trip because the charging current was well over 50A. If you had started drawing current from the leisure battery with your lighting etc, its voltage would have dropped somewhat, but the vehicle battery was in a good state of charge with the alternator pushing its voltage up. At the moment of relay closure there can be a short period of very high charging current while the voltages of the leisure and vehicle batteries equalise. This might not have happened previously when testing the split charging, because the leisure battery had been more fully charged before you had installed the fuse box and started taking current from it.

Check the voltages of the two batteries (can be done at the two sides of the relay contacts) just before starting, then once the relay closes watch the leisure battery voltage and if it climbs towards the alternator voltage but the circuit breaker still trips, it's probably just too small for the combination of large leisure batt capacity in good condition and the available charging current. If either side of the system shows an abnormally low voltage, then further investigation is needed for faults.

If the breaker trips when cranking the engine, it means the relay is not opening when the alternator stops and some of the cranking current is being drawn from the leisure battery. This can be a problem with straight voltage sensing relays that are not interlocked with the alternator charge warning. Any delay in opening after stopping the engine due to high battery terminal voltage that allows even a second of cranking on the leisure battery during a restart, gives an opportunity for the breaker to trip.

Hi Lucien,

Thanks for this. I think you are correct. I did the earthing of leisure batteries and split charge relay again and ensure they were on bare metal, separately and tight fitting and this seemed to have the the split charge relay "want to start working". I started engine then checked engine battery and leisure battery with multimeter and leisure battery was very low, probably as you say to me doing a lot of wiring up. I then closed circuit breaker, it tripped again but I closed it again and then it stayed shut and soon after the split charge relay kicked in.

So, do you think I should change circuit breaker from 50 amp to 100 amp. Yes, the circuit breaker is wired in series, I THINK, as in it is in the same wiring line between the 100 amp fuse just after engine battery and just before the split charge relay. This is a link to circuit breakers I used. https://www.amazon.co.uk/gp/product/B078TDZ8J9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Wiring is 16mm2 and seems good quality. So in short, are you saying the reason this occurred is because I let leisure battery drain well below engine battery without a method of topping up through engine running or solar panel feed?

 

[afarr86]

Have you got a smart alternator?
Are the leisure batteries grounded to the chassis?

This vid might help

Hi,

Yes, I saw this on youtube - good tutorials from this guy

Yes, one think I did that probably helped was I ensure leisure battery earth and split charge relay earth was on bare metal of vehicle body and tightly fixed

Thanks. I am still learning about camper electrics - just started, but interesting and has its challenges

 

[Lucien Nunes]

I closed it again and then it stayed shut and soon after the split charge relay kicked in.

This is the bit that doesn't quite make sense. Unless there is a short, which you would know about because of the shower of sparks and blown fuse, the circuit breaker won't trip until the split charge relay closes and starts passing heavy current through it to the leisure battery. I suspect that the relay had already closed after you started the engine, normally it will only take a second or two, and that caused the first trip. The second time you reset the breaker, you were more aware of the relay closing because the breaker didn't trip.

It just seems that the 50A circuit breaker is undersized and that the vehicle is capable of charging the leisure battery at a higher rate when the battery demands it, tripping the breaker. Those automotive circuit breakers are not made to any recognised standards so it is impossible to say how accurate they are with respect to tripping current. I have seen similar types that were definitely not calibrated correctly, so personally I don't use them.

If you want to be able to disconnect the split charging system from the vehicle, by all means fit a switch, but I don't see a need for a circuit breaker here if the cabling is protected at both ends by fuses. Obviously it is not usual to protect both ends of a cable but in this situation there is an energy source at both ends. Many would not bother to fit the fuses either, because if properly installed the chances of that cable being short-circuited are very low. I approve of the fuses, but the resistance of additional components adds up and the charging feed is much more sensitive to additional resistance than ordinary load circuits, so I would avoid putting too many fuses and circuit breakers in line.

Regarding 'earth' connections, don't forget that when we speak of 'earth' in a vehicle context, it's shorthand for 'negative connection via the bodywork' and is an economy adopted by all vehicle makers, to save running a negative wire from things back to the battery / engine block. There's nothing special about using the vehicle body as a means of connection, it's not really 'earth', just a cheap'n'cheerful alternative to a length of black cable. In marine work it is prohibited to pick up negative connections from the hull metalwork because it accelerates corrosion and disrupts compasses, so both positive and negative must be run as cables back to the source.

 

[OnlQQker]

This is the bit that doesn't quite make sense. Unless there is a short, which you would know about because of the shower of sparks and blown fuse, the circuit breaker won't trip until the split charge relay closes and starts passing heavy current through it to the leisure battery. I suspect that the relay had already closed after you started the engine, normally it will only take a second or two, and that caused the first trip. The second time you reset the breaker, you were more aware of the relay closing because the breaker didn't trip.

It just seems that the 50A circuit breaker is undersized and that the vehicle is capable of charging the leisure battery at a higher rate when the battery demands it, tripping the breaker. Those automotive circuit breakers are not made to any recognised standards so it is impossible to say how accurate they are with respect to tripping current. I have seen similar types that were definitely not calibrated correctly, so personally I don't use them.

If you want to be able to disconnect the split charging system from the vehicle, by all means fit a switch, but I don't see a need for a circuit breaker here if the cabling is protected at both ends by fuses. Obviously it is not usual to protect both ends of a cable but in this situation there is an energy source at both ends. Many would not bother to fit the fuses either, because if properly installed the chances of that cable being short-circuited are very low. I approve of the fuses, but the resistance of additional components adds up and the charging feed is much more sensitive to additional resistance than ordinary load circuits, so I would avoid putting too many fuses and circuit breakers in line.

Regarding 'earth' connections, don't forget that when we speak of 'earth' in a vehicle context, it's shorthand for 'negative connection via the bodywork' and is an economy adopted by all vehicle makers, to save running a negative wire from things back to the battery / engine block. There's nothing special about using the vehicle body as a means of connection, it's not really 'earth', just a cheap'n'cheerful alternative to a length of black cable. In marine work it is prohibited to pick up negative connections from the hull metalwork because it accelerates corrosion and disrupts compasses, so both positive and negative must be run as cables back to the source.

Hi Lucien,
does coming from the + and - from the battery and not using the chassis make any difference to keeping the batteries balanced with the cables + and - being the same length?
Also running from the fusebox the same?

Or does it make no difference.

 

[Lucien Nunes]

The bodywork is just another conductor. If you provide a negative cable to the engine block (i.e. to the alternator) of the same resistance as the bodywork, the system will behave in the same way. Although steel is not anywhere near as good a conductor as copper, usually there is a large cross-section available. Depending on the location within the vehicle, it can take quite a large copper cable to provide as a low a resistance connection as a lug onto the vehicle chassis or body nearby. Offset against that low resistance available for free, is the downside that connections to bared steel in a vehicle environment can be subject to corrosion. You might get a nice low resistance connection to begin with, but after years of exposure to road spray, body 'earth' connections are notoriously unreliable, whereas a proper insulated return wire might be completely immune to the environmental effects.

So I would say any really solid connection to the bodywork will be absolutely fine for the auxiliary battery system. But if I were installing it within a few feet of the engine block, I would probably run the negative connection back there with another length of 16mm², simply to avoid possible corrosion problems at the body connection in the future. I am biased in favour of wired negative returns, as most of the 12V and 24V installation I have ever done has been in marine applications where it is mandatory.

You mention making +ve and -ve cables the same length. The reason for doing this and having them follow exactly the same route, is to avoid creating magnetic fields that upset compasses and fluxgate sensors. If a positive feed runs down one side of a vessel, but the negative of that circuit either runs down the other, or uses the hull in which case the current will be spread out throughout the whole cross-section of the steel, it forms a single-turn coil which produces a field in proportion to the current flowing. The greater the area enclosed within that loop, the greater the magnetic effect. Ideally, the two conductors want to occupy the exactly same path through space, just as with data cables, aerials etc where the loop area has to be minimised to prevent interference emission and pickup. Standards such as ethernet and HDMI achieve this by twisting the two conductors of each circuit together, which makes them follow the same mean effective path along the centreline of the twist, when averaged along their length. Aerial cables achieve a similar result by being coaxial - the 'average' location of the shield is in its centre, where the signal conductor is. For power cables it is usually sufficient to run them adjacent so that a minimum area is enclosed by the loop thus formed, but there are arguments for using twisted power cables if heavy currents need to run near to magnetic sensors.

This is somewhat related to the argument against single-core and earth wiring for domestic lighting circuits, and other schemes in which the current along one cable is unbalanced e.g. 'traditional' 2-way switching. In the days of incandescent lamps, the current in the cables was purely sinusoidal and although loops enclosing area were formed, the interference radiated was minimal. However, with SMPSU drivers running from these circuits, large loops are more likely to radiate any wideband noise they generate and spit out through their mains inputs.