Battery/electric wildcamping

[snowdrops]

We've more or less decided on a layout for our conversion......... not that we're ever gonna decide on where to have this done !!!! One of the potential converters said we didn't need a 3-way fridge as he'd fit a relay. My question is, given that we intend to wildcamp most of the time, what is the best way to provide charge/electric to van ? Obviously gas for cooker is easy. But what about the rest ?

Main issues would be ....... keeping fridge running, needing to plug in the ipod dock so we can have music, using hairdryer where possible, microwave now and then, odd charging of lappy and daily charging of phones, (tho we cld do that from ciggy lighter thing).

 

[Ed Excel]

A starter battery will read over 13.7v almost straight away when the alternator starts to work. It doesn't mean the starter battery is fully charged.

Mitzimad is right, unless the specific relay your referring to is a lot smarter than the ones I've used in the past.

I don't imagine the manufacturer is suggesting the starter battery is fully charged at 13.7V. I read it as being the trigger voltage for the alternator to commence charging.

The manufacturer's statement, in my previous posting, clearly states the starter battery is charged first. Otherwise, I don't see the point of a relay.

 

[Wissel]

From my understanding the reason for a relay is to stop the starter battery being flattened when parked up by appliances in the habitation area.

The relay opens when it reads a higher voltage from the starter battery - when the engine is running. This allows the habitation battery to charge from the alternator.

When the engine is switched off, the voltage drops and the relay closes. If the relay isn't closed there would be nothing stopping, say the TV, flattening the habitation battery and the starter battery.

That's the point to the relay - it protects the starter battery.

It can't tell that the starter battery is full before charging the habitation battery, this would need something a lot cleverer than a relay.

All this means that when the engine is running, the relay opens and the starter battery and habitation battery are both charged at the same time.

 

[Ed Excel]

[HI][/HI]

From my understanding the reason for a relay is to stop the starter battery being flattened when parked up by appliances in the habitation area.

[HI]The relay opens when it reads a higher voltage from the starter battery - when the engine is running. This allows the habitation battery to charge from the alternator.[/HI]

When the engine is switched off, the voltage drops and the relay closes. If the relay isn't closed there would be nothing stopping, say the TV, flattening the habitation battery and the starter battery.

That's the point to the relay - it protects the starter battery.

[HI]It can't tell that the starter battery is full before charging the habitation battery, this would need something a lot cleverer than a relay. [/HI]

All this means that when the engine is running, the relay opens and the starter battery and habitation battery are both charged at the same time.

Haven't you described how the relay determines when the starter battery is full in your first statement highlighted?

Modern relays sence the battery voltage whereas, older types used a connection to the alternator.

 

[Wissel]

Haven't you described how the relay determines when the starter battery is full in your first statement highlighted?

Modern relays sence the battery voltage whereas, older types used a connection to the alternator.

No

A full battery is around 12.7v

The way a battery is charged is by throwing a higher current at it (this is the same for an alternator, solar or a 240v charger)

So when the engine is switched on the alternator starts and this takes the voltage of the starter battery over 13.7v within a few seconds.

This does not mean the starter battery is full, simply that it is charging.

The relay sees the higher voltage from the alternator and opens.

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[Ed Excel]

No

A full battery is around 12.7v

The way a battery is charged is by throwing a higher current at it (this is the same for an alternator, solar or a 240v charger)

"I'm sure you meant voltage".

So when the engine is switched on the alternator starts and this takes the voltage of the starter battery over 13.7v within a few seconds.

"Depends on the initial battery voltage. It may take some time to reach full charge. The voltage you will see, in a short time after starting the engine, is the alternator voltage".

This does not mean the starter battery is full, simply that it is charging.

The relay sees the higher voltage from the alternator and opens.

"Shouldn't the relay close to start charging the leisure battery"?

"I suspect we're talking about two different animals.

Modern voltage sensing split charge relays operate differently to older types that needed a cable connection to the alternator to operate".

 

[TheBig1]

the other very important thing a split charge relay does, whether voltage sensing or acc triggered, is to isolate the leisure battery from the starting circuit. the starter motor draws a very high current to start the engine. having the leisure battery directly connected would find the starter drawing high current from it potentially damaging both it and the wiring. look at the thickness of the starter cable on the engine battery and the thin wire charging the leisure battery.

the cold cranking current CCA of a starter battery is determined by a few things but mostly the plates in the battery. a leisure battery cannot handle that current, especially for a large diesel engine.

modern voltage sensing split charge relays are designed with a circuit built in that can be adjusted to only switch on at the point the engine battery reaches 13.8volts. at this point, the alternator on a modern vehicle also senses the reduction in current and reduces its output to a maintenance level to cope with lights and other accessories. this is the basic reason why an upgraded alternator or a battery to battery charger is best fitted when large banks of leisure batteries are present. the B2B appears to the alternator and its circuit as a continuation of the starter battery so keeping the output higher and charging the leisure battery at near full alternator current

this is the reason for seeing these fitted otherwise an 80amp or 100amp alternator will only charge the leisure batteries at a limited 10amp. obviously taking a 400amp/hour battery bank for example it would take 2hours to charge with B2B or up to 20hours on a standard split relay if depleted to half capacity.

it always amazes me when people fit extra batteries and are then surprised that it takes so long to achieve full charge

with solar panels, the charge current will be there all the time the sun shines on them so will normally keep pace with most domestic use of the batteries. and only reduces when the regulator senses the batteries are reaching capacity

there is far more to charging batteries than the average person realises:thumb:

 

[Wissel]

The relay is closed when it is not charging the habitation battery.

The relay opens when it sees over a certain voltage (13.7v in this case)

When the alternator starts to charge the starter battery, the starter battery voltage will go above 13.7v within a few seconds.

Anything that reads the battery voltage will, at this point, also see over 13.7v so if a relay is connected to the starter battery and the alternator is running the relay will open and charge the starter and habitation battery at the same time.

I don't think I'm explaining it very well so here is a very quick video showing the voltages.

[ame="http://www.youtube.com/watch?v=bMm8IbYXkkg&feature=youtu.be"]Battery Voltage Video - YouTube[/ame]

Of course I don't have an alternator in my studio but a battery charger does exactly the same.

Hope that explains it better,
David

 

[mitzimad]

wether the relay is voltage sensing or triggered by a wire from the alternater or from the canbus as soon as the vehile is started the alternator will start to pump out around 14 volts as this is above the charge voltage of both batteries the relay will make and the voltage from the alternator will go to both batteries charging levels are decided by the alternator regulator but power will only go to both batteries the relay will only close when the alternator cuts back its out put either when both batteries are fully charged or the engine is stopped

 

[Ed Excel]

wether the relay is voltage sensing or triggered by a wire from the alternater or from the canbus as soon as the vehile is started the alternator will start to pump out around 14 volts as this is above the charge voltage of both batteries the relay will make and the voltage from the alternator will go to both batteries charging levels are decided by the alternator regulator but power will only go to both batteries the relay will only close when the alternator cuts back its out put either when both batteries are fully charged or the engine is stopped

Agreed apart from:
The point of a voltage sensing relay is to provide an improved charging regime, compared to a simple changeover relay. The alternator does not initially charge the leisure battery, with voltage sensing types (please see #29). Older types of relay did and this was the main reason for the advise to have comparable batteries that are electrically the same. With a modern VSR matching the batteries should not matter as much, because the batteries are charged seperately.

I think the two different types of relay are being confused.

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[Wissel]

A voltage sensing relay does exactly what is says.

It senses the voltage.

When a battery is put on charge (in this case by an alternator) the voltage of the battery will rise almost instantly (see the video above if you don't believe me).

The voltage sensing relay sees the higher voltage of the starter battery and engages.

The relay has no way of knowing if the starter battery is full or not.

Whether the starter battery is full or not, once the alternator is running, the starter battery voltage will rise and both the starter battery and the habitation battery will be charged at the same time.

There does seem to be a few articles on the net that have this confused, I assume they think that the starter battery voltage goes up AS its being charged reaching a peak WHEN its charged.

This is not correct (and neither are the articles), the battery voltage goes up almost straight away (within seconds) whether fully charged or not. This is how a battery charges.

 

[snowdrops]

Got a bit technical hasn't it ? oh: Phew ! Can see peeps really know their stuff here.

However, to quote part of a discussion I've found useful.............. "how long would it last off a leisure battery then?"

"I have no problems getting 48 hours use from a compressor fridge without moving the van. I suspect 3 days would be no problem. This is with a 100A battery and mostly LED lights. Fridge is a vitrifrigo 39lt, but basically the same compressor as the waeco's so they would be similar consumption."...........

I've read a fair few similar ones and defo giving it a go. I'll keep you posted when we start travelling about, even if that means letting you know we're stuck in the middle of nowhere with flat battery

 

[mitzimad]

provided you have a split system youll not be stuck as the whole point of the split is to stop the vehicle battery being flattened by the equipment in the hab area