What sort of charge would the caravan battery get if you travel around 4 hours?
is it possible to estimate the amount of amps that would be put back into the caravan battery?
oldbloke said
10:21 PM Apr 11, 2021
Only way to find out is to try it. Every system is different.
I had a 100ah battery in mine until recently. After about 3 hours driving was pretty well fully charged from almost flat.
Whenarewethere said
10:25 PM Apr 11, 2021
It depends on the hardware how much charge the battery is getting.
Even basic things like the correct size wiring will make all the difference.
A good starting point is get a DC clamp meter, or at the very least an amp meter.
What sort of charge would the caravan battery get if you travel around 4 hours?
is it possible to estimate the amount of amps that would be put back into the caravan battery?
Depends if your car's alternator allows charging to the caravan battery. A lot of modern cars these days do not allow charging to a secondbattery for various reasons. It turns off the alternator when it senses the starter battery has reached it limit.
That would be the first thing I would find out from an Automotive Electrician. It can be changed and legally done.
After that it's anyone guess.
Jaahn said
08:33 AM Apr 12, 2021
aastek wrote:
What sort of charge would the caravan battery get if you travel around 4 hours?
is it possible to estimate the amount of amps that would be put back into the caravan battery?
Hi
The best charger you have is your car alternator. It is quite capable of charging a normal caravan battery in 4 hours. However you do need to get the details correct as mentioned already. As you have not said how big your battery is I assume it is about 100-120AHr. Most car alternators are around 80-100A or more.
First the later vehicles have variable voltage alternators that drop the charging rate after the car battery is recharged, so you do need to find out if you have that silly feature. If so you need to use a DC-DC charger and it has to be a larger size 40A to charge up in 4 hours. There might be other options also.
The wiring has to be fitted professionally to carry the current and suitable plugs etc so it will work OK. As the distance from the engine to the van battery and return is at least 10M or more heavy wire is required.
If you told us what vehicle and what sized battery you have then people here that have done a similar setup could advise you more.
Good luck Jaahn
aastek said
09:10 AM Apr 12, 2021
Jaahn
Yep I did indeed leave out the basic details of my current setup and I did realise that I was asking how long a piece of string was. I was trying to get a rough idea but now know that there are so many variables in this quest for knowledge, size of car alternator, length and size of wiring etc
I have a 115ah battery and the tow vehicle is a Nissan 2012 Pathfinder and the wiring was installed by a caravan company.
I will get an amp meter
Thanks everyone for the help and I too love the crystal ball !!
Whenarewethere said
09:57 AM Apr 12, 2021
Radar wrote:
aastek wrote:
What sort of charge would the caravan battery get if you travel around 4 hours?
is it possible to estimate the amount of amps that would be put back into the caravan battery?
Depends if your car's alternator allows charging to the caravan battery. A lot of modern cars these days do not allow charging to a secondbattery for various reasons. It turns off the alternator when it senses the starter battery has reached it limit.
That would be the first thing I would find out from an Automotive Electrician. It can be changed and legally done.
After that it's anyone guess.
Smart alternators on modern cars are an issue.
My car has a very stable 14.4 volts. Depending on the accessories my car comes with a 130 or 150amp alternator. Typically about 80amps out of my 130amp alternator, but there are an awful lot of things on a modern car to run let alone charging an auxiliary battery along 24 metres of wiring (2 x 12m both + & - ) in a caravan!
Whenarewethere said
10:28 AM Apr 12, 2021
aastek wrote:
Thanks everyone for the help and I too love the crystal ball !!
I actually bought a very transparent crystal ball & drag it out when people asked various questions. It actually worked quite well..... getting better questions!
Mate that won't work it isn't the crystal ball it's just made of crappy glass
peter67 said
04:38 PM Apr 12, 2021
No wukkers, just look at it through a crystal wine glass.
Whenarewethere said
04:46 PM Apr 12, 2021
I had it at work & when I got asked impossible questions I said I have a crystal ball & pulled it out of the draw.
People had a laugh & then were far more precise.
So it did really work!
Peter_n_Margaret said
05:01 PM Apr 12, 2021
aastek wrote:
Yep I did indeed leave out the basic details of my current setup and I did realise that I was asking how long a piece of string was. I was trying to get a rough idea but now know that there are so many variables in this quest for knowledge, size of car alternator, length and size of wiring etc
The important bits are the voltage output of the alternator, the length of the cables between the alternator and the battery and the size of those cables.
Charge rate is determined by the difference between the voltage delivered and the battery voltage and the internal battery resistance.
No crystal balls.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Monday 12th of April 2021 05:02:12 PM
Tony LEE said
07:35 PM Apr 12, 2021
Good luck on using maths to figure it all out, simply because the two important factors are not fixed. Many alternators do not have constant voltage output and it can be very dependant on alternator temperature and condition of starter battery and on other vehicle power consumption.
On the other end of that long skinny undersized wire is a battery which has ever-changing impedance/terminal voltage so...
Of course a DC2DC charger with properly sized wiring gets rid of all the variability, but without it the van owner will usually be very disappointed to find that even at a cold start the charging current might get at high as 15 amps for the first 10 minutes and as low as 5 amps after an hour.
Jaahn said
08:31 PM Apr 12, 2021
Hi aastek
According to Redarc your car has a variable voltage alternator so will need a BCDC charger. ; https://www.redarc.com.au/forum/discussion/58/2012-d40-navara-dual-battery-charging
Possibly you have tried to charge your van battery with no success, if so now you know why it does not work. If you want to use the van batteries full capacity my advice is the bigger unit but if you are a smaller user the smaller one might be OK.
I would recommend that you check the size of the wiring and plug fitted to ensure it is good enough also. It is important that the caravan supply wiring is connected to the car battery correctly so the alternator will sense the increased current needed.
Good luck jaahn
PS I also believe a multimeter is very useful. I have three ! Get one with a current clamp as suggested. Learn to use it properly and no wiring difficulty will be a problem
-- Edited by Jaahn on Monday 12th of April 2021 08:35:39 PM
-- Edited by Jaahn on Tuesday 13th of April 2021 08:21:05 AM
Dicko1 said
10:27 AM Apr 13, 2021
If people travelling/camping with 12 volt systems just took some time to know how their system works, some basic solar/battery knowledge and had some knowledge about what is going on with their system...half the internet forums would cease to exist....
Whenarewethere said
10:45 AM Apr 13, 2021
Dicko1 wrote:
If people travelling/camping with 12 volt systems just took some time to know how their system works, some basic solar/battery knowledge and had some knowledge about what is going on with their system...half the internet forums would cease to exist....
Agree, but it is a lost cause.
People don't know where the engine is in their car & don't know that tyres have air in them.
The number of people I have jump started in my street is staggering & a good percentage were amazed you could do that from another car.
Ignorance & stupidity is the only expanding base!
Also plugged 2 tyres in my street & the people were blown away!
Basic knowledge & survival skills went out the window long ago.
Only a few weeks ago I towed a truck with 3 tonnes of roof tiles off the neighbours front lawn as it had got bogged.
I could see the builders were quietly laughing amongst themselves at this little Freelander. Smirks were quickly wiped away when I saved then $300, only cost them a case of beer!
Paper & pencil to do a basic wiring sketch. No hope!
Whenarewethere said
10:52 AM Apr 13, 2021
A couple in our building I jump started their car, otherwise I would have been helping delivering their baby. It's got this bad!
Actually she is a good looker but it may have been a bit embarrassing for her in the long run!
Hylife said
09:15 PM Apr 16, 2021
On most modern vehicles manufactured after January 1 2015, very little charge indeed. Why?
As a UN signatory to ECE emission rules, all motor vehicles manufactured for a UN member country after 01/01/2015 must have a so called "smart alternator". Basically they found that for cranking you don't need a full charge and if you tell folks that automotive batteries only last 3 years, then it doesn't shorten the battery life significantly.
So, your modern day smart alternator will only charge your crank battery 'with' 13.4 volts and this is nowhere near the required 14.4 volts to fully charge a "non-crank" battery.
Now add the expected voltage drop over the very long run of 7 to 10 meters of wiring. (over a given diameter of wire, Voltage drop increases as the current increases) Unless you are using 14 square mm heavy duty copper wiring (6B&S minimum, not the outer insulation, the actual wire), your multimeter is going to show you zero drop under no load, but about 1.5volts drop at 25 amps or more,
Yep, your 13.4 is now down to 11.9 volts, and that just isn't going to charge your house battery one iota.
This is why folks install DC-DC chargers, to boost the long run voltage up so you can actually use that 25+ amps.
I have used to have two DC-DC chargers, one under the front passengers seat for charging the under bonnet auxiliary 100ah flooded deep cycle N70T, and one in the van next to the two 120ah AGM's. Since going to LiFePO4 (2x100ah drop-ins in parallel) I now don't need the one in the van, my 450watts of solar is enough even on overcast days, being about 30% more efficient into low internal resistance batteries.
Whenarewethere said
09:50 PM Apr 16, 2021
Hylife wrote:
Now add the expected voltage drop over the very long run of 7 to 10 meters of wiring.
& to bang on this subject again. Wire resistance is the total length of + & -
So 7 to 10 metres when calculating resistance is 14 to 20 metres, & a bit more for each the connection.
I calculated a voltage loss of 0.17 volts just inside my fridge alone, so upgraded the internal wiring.
Thin wire from the solar panels, to the fridge, within the fridge, & some wonder why things are not working very well.
oldbloke said
07:49 AM Apr 17, 2021
I heard if you turn on your car parking lights it tricks the alternator to increase the charge voltage. And this helps to charge the house battery. Would this help?
Jaahn said
08:08 AM Apr 17, 2021
oldbloke wrote:
I heard if you turn on your car parking lights it tricks the alternator to increase the charge voltage. And this helps to charge the house battery. Would this help?
Hi oldbloke
Well on my car the parking lights are not enough to get the voltage right up. But putting the full lights on does it and gets it up to 14.2V and I do sometimes do that as I go home to top-up the battery. Possibly it varies between different brands depending on the genius designer.
What sort of charge would the caravan battery get if you travel around 4 hours?
is it possible to estimate the amount of amps that would be put back into the caravan battery?
I had a 100ah battery in mine until recently. After about 3 hours driving was pretty well fully charged from almost flat.
It depends on the hardware how much charge the battery is getting.
Even basic things like the correct size wiring will make all the difference.
A good starting point is get a DC clamp meter, or at the very least an amp meter.
One could easily do a bit of homework.
What size alternator does the car have. Look up the manufacturer's data, easy.
What size battery does the caravan have.
What is the wiring length. You need this to calculate wire resistance.
What is the cross sectional area of each the wiring sections. Again you need this to calculate resistance.
What is the car's voltage:
- At the car's battery.
- At the towbar.
- At the caravan's battery.
While the engine is running.
What size is the DC-DC charger, if you have one.
Is the DC-DC charger next to the caravan's battery where it should be.
Anyone who doesn't have a at least a cheap Jaycar or similar multimeter should be hung, drawn & quartered!
This is as basic as not carrying extra fuses!
A cheap DC clamp meter:
https://www.jaycar.com.au/600a-true-rms-ac-dc-clamp-meter/p/QM1632
One should really know this basic stuff to make the crystal ball easier to read!
My DC clamp meter. The next best piece of equipment after TPMS.
Simple amp & voltage analogue meters in my car. Not difficult stuff.
Depends if your car's alternator allows charging to the caravan battery. A lot of modern cars these days do not allow charging to a secondbattery for various reasons. It turns off the alternator when it senses the starter battery has reached it limit.
That would be the first thing I would find out from an Automotive Electrician. It can be changed and legally done.
After that it's anyone guess.
Hi
The best charger you have is your car alternator. It is quite capable of charging a normal caravan battery in 4 hours. However you do need to get the details correct as mentioned already. As you have not said how big your battery is I assume it is about 100-120AHr. Most car alternators are around 80-100A or more.
First the later vehicles have variable voltage alternators that drop the charging rate after the car battery is recharged, so you do need to find out if you have that silly feature. If so you need to use a DC-DC charger and it has to be a larger size 40A to charge up in 4 hours. There might be other options also.
The wiring has to be fitted professionally to carry the current and suitable plugs etc so it will work OK. As the distance from the engine to the van battery and return is at least 10M or more heavy wire is required.
If you told us what vehicle and what sized battery you have then people here that have done a similar setup could advise you more.
Good luck Jaahn
Yep I did indeed leave out the basic details of my current setup and I did realise that I was asking how long a piece of string was. I was trying to get a rough idea but now know that there are so many variables in this quest for knowledge, size of car alternator, length and size of wiring etc
I have a 115ah battery and the tow vehicle is a Nissan 2012 Pathfinder and the wiring was installed by a caravan company.
I will get an amp meter
Thanks everyone for the help and I too love the crystal ball !!
Smart alternators on modern cars are an issue.
My car has a very stable 14.4 volts. Depending on the accessories my car comes with a 130 or 150amp alternator. Typically about 80amps out of my 130amp alternator, but there are an awful lot of things on a modern car to run let alone charging an auxiliary battery along 24 metres of wiring (2 x 12m both + & - ) in a caravan!
I actually bought a very transparent crystal ball & drag it out when people asked various questions. It actually worked quite well..... getting better questions!
I had it at work & when I got asked impossible questions I said I have a crystal ball & pulled it out of the draw.
People had a laugh & then were far more precise.
So it did really work!
The important bits are the voltage output of the alternator, the length of the cables between the alternator and the battery and the size of those cables.
Charge rate is determined by the difference between the voltage delivered and the battery voltage and the internal battery resistance.
No crystal balls.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Monday 12th of April 2021 05:02:12 PM
Hi aastek
According to Redarc your car has a variable voltage alternator so will need a BCDC charger. ; https://www.redarc.com.au/forum/discussion/58/2012-d40-navara-dual-battery-charging
Possibly you have tried to charge your van battery with no success, if so now you know why it does not work. If you want to use the van batteries full capacity my advice is the bigger unit but if you are a smaller user the smaller one might be OK.
I would recommend that you check the size of the wiring and plug fitted to ensure it is good enough also. It is important that the caravan supply wiring is connected to the car battery correctly so the alternator will sense the increased current needed.
Good luck jaahn
PS I also believe a multimeter is very useful. I have three ! Get one with a current clamp as suggested. Learn to use it properly and no wiring difficulty will be a problem
-- Edited by Jaahn on Monday 12th of April 2021 08:35:39 PM
-- Edited by Jaahn on Tuesday 13th of April 2021 08:21:05 AM
If people travelling/camping with 12 volt systems just took some time to know how their system works, some basic solar/battery knowledge and had some knowledge about what is going on with their system...half the internet forums would cease to exist....
Agree, but it is a lost cause.
People don't know where the engine is in their car & don't know that tyres have air in them.
The number of people I have jump started in my street is staggering & a good percentage were amazed you could do that from another car.
Ignorance & stupidity is the only expanding base!
Also plugged 2 tyres in my street & the people were blown away!
Basic knowledge & survival skills went out the window long ago.
Only a few weeks ago I towed a truck with 3 tonnes of roof tiles off the neighbours front lawn as it had got bogged.
I could see the builders were quietly laughing amongst themselves at this little Freelander. Smirks were quickly wiped away when I saved then $300, only cost them a case of beer!
Paper & pencil to do a basic wiring sketch. No hope!
A couple in our building I jump started their car, otherwise I would have been helping delivering their baby. It's got this bad!
Actually she is a good looker but it may have been a bit embarrassing for her in the long run!
On most modern vehicles manufactured after January 1 2015, very little charge indeed. Why?
As a UN signatory to ECE emission rules, all motor vehicles manufactured for a UN member country after 01/01/2015 must have a so called "smart alternator".
Basically they found that for cranking you don't need a full charge and if you tell folks that automotive batteries only last 3 years, then it doesn't shorten the battery life significantly.
So, your modern day smart alternator will only charge your crank battery 'with' 13.4 volts and this is nowhere near the required 14.4 volts to fully charge a "non-crank" battery.
Now add the expected voltage drop over the very long run of 7 to 10 meters of wiring. (over a given diameter of wire, Voltage drop increases as the current increases)
Unless you are using 14 square mm heavy duty copper wiring (6B&S minimum, not the outer insulation, the actual wire), your multimeter is going to show you zero drop under no load, but about 1.5volts drop at 25 amps or more,
Yep, your 13.4 is now down to 11.9 volts, and that just isn't going to charge your house battery one iota.
This is why folks install DC-DC chargers, to boost the long run voltage up so you can actually use that 25+ amps.
I have used to have two DC-DC chargers, one under the front passengers seat for charging the under bonnet auxiliary 100ah flooded deep cycle N70T, and one in the van next to the two 120ah AGM's.
Since going to LiFePO4 (2x100ah drop-ins in parallel) I now don't need the one in the van, my 450watts of solar is enough even on overcast days, being about 30% more efficient into low internal resistance batteries.
& to bang on this subject again. Wire resistance is the total length of + & -
So 7 to 10 metres when calculating resistance is 14 to 20 metres, & a bit more for each the connection.
I calculated a voltage loss of 0.17 volts just inside my fridge alone, so upgraded the internal wiring.
Thin wire from the solar panels, to the fridge, within the fridge, & some wonder why things are not working very well.
Hi oldbloke
Well on my car the parking lights are not enough to get the voltage right up. But putting the full lights on does it and gets it up to 14.2V and I do sometimes do that as I go home to top-up the battery. Possibly it varies between different brands depending on the genius designer.
Jaahn