We have a camper with 2x100 amh batteries and 250 watt solar panels so far we have not had any issues with the batteries not getting enough charge, however we do live in Queensland. We are planning a trip south and I am expecting the sun to stay in Queensland and not follow us. Would a DC to DC charger be enough and will I have to run a separate Anderson plug for the solar panels or can I run the one Anderson plug which will charge from the tow vehicle as well as the solar panels through the DC to DC charger. This is a general question and hard to answer without talking about how much power is used, size of the fridge etc etc but just thought I would get general feedback from other peoples experiences.

Cheers

Martin and Denise 

Hi Martin 

You need to give a lot more details,to get worthwhile relavant suggestions

What is your present set up?

[1]Do you have a good charging set up for charging direct from the alternator

[2]What is the output voltage of your vehicle alternator

[3]What size cables are used ALL the way from alternator the van batteries

[4]Van batterteies

[5]What do you hope to use & for how long before being connected to mains power

DO NOT rush into buying a DC/ Dc charger until you make sure your current set up cannot be improved.

 Perhaps it should also be noted that Intervolt recommend 6 B&S cable for the interconnections

I bet the van in question does not have 6B&S cables ALL the way,& that may be all you need for your set up 

You will also be limited to a MAX output current of 25A ,so better not run a 12V absortion fridge  of the van battery while tring to charge it 

Martin_QLD wrote:

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So I have looked into this and got some advise from places like battery world and ARB and it has blown out somewhat. Something I forgot to mention is we also charge with 240v as well as a vehicle Anderson plug and 250w solar. what the recommendations are is to put a Red Arc battery management system in, the red arc battery management 30 system. The cost is around $2000 without fitting the unit, although I believe this could be a good unit I am still not convinced that when free camping in the southern states I am going to produce enough power to be sustainable over say a week with solar without either hoking it up to the car or finding a power source. Although I really dont want to go the way of a generator, (carrying more fuel, noise and convenience) I cant see a way around it and for $2000 I could be a brand named generator. Happy to get opinions and suggestions so I can work through to the best outcome because once we leave it will be too late.

Thanks in advance.

Martin

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Hi Martin

Yes, you can spend big money based on false advise especialy fromsome one who will gain from that advise,& sadly it may not be the real answer

I personally would be shying very clear of anyone who suggested spending that sort of money for just the charging control system unless it included a BIG battery bank

 There are the factors that need to be considered before any real  cost effective decisions can be made

[

Below are the esential steps, in order

[1]Your expected daily amphr  power consumption , Amphrs ,when away from mains charging

Make a list of all 12V power drawing devise , find wattage, divide that by 12 ,multiply by expected hours of operation per 24hr day

Total ALL results

[2]Your available battery capacity[actual amphrs available when fully charged, not total rated capacity. This will depend on battery type

[3]numbern of expected days with no other means of charging except solar

[4]your alternator type ,output voltage

[5]when travelling, the likely shortest drive period [hours] per day

[6]the longest period you expect to camp away from overnight mains power .

[7]Your Mains charger amphr capacity

Those are the essential points to consider!

Now,no matter which line you take, what you should do FIRST is:

[a]To have a twin 6B&S cable [13mm Sq cross sectional area] ran ALL THE WAY from your alternator to the van battery

Then

If you are running a 3way fridge on 12v while travelling ,ditto with a totally seperate circuit for that

In both caes with an isolator to disconnect when engine is not running

That may or may not be built into the 3way fridge depending on model

You Will require  those even IF you finally determine you do need a DC/Dc charger

Perhaps even requiring a 40A DcDC charger

or you could take the easy path &   perhaps not get the results. you may need

Remember apart from low  sun ,there could be days of no sun, so battery capacity needs to be available to meet those situations

You'll get close if you double your solar ? Maybe one more battery ? Then just be prepared for cloudy or overcast days . I assume you have gas for cooking, possibly 3 way fridge ? Yes the quotes I got to upgrade or to fix was nearly heart attack material !! Sales people NOT  tech !! Not "all" generators are noisy ! So many options that are not necessary expensive . Another 150 or 200 amp alternator off tug ? Just to charge big time ? When desperately required is another option . Other than that a generator connected to excercice bike ?? You tend to use more power on cloudy days too ! Ahhhh !! Weight is another consideration !! Ahhh !!

Martin_QLD wrote:

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We have a camper with 2x100 amh batteries and 250 watt solar panels so far we have not had any issues with the batteries not getting enough charge, however we do live in Queensland. We are planning a trip south and I am expecting the sun to stay in Queensland and not follow us. Would a DC to DC charger be enough and will I have to run a separate Anderson plug for the solar panels or can I run the one Anderson plug which will charge from the tow vehicle as well as the solar panels through the DC to DC charger. This is a general question and hard to answer without talking about how much power is used, size of the fridge etc etc but just thought I would get general feedback from other peoples experiences.

Cheers

Martin and Denise 

---

A second look now we have returned from our trip to Sydney and back. If you already have 250w of solar then you must also have a solar regulator, so I see no reason to duplicate that. If the question is can an additional 250w of portable panels be used through the same set up (Anderson plug) as a DC to DC link from the alternator then the answer is yes. I'm assuming you would use the alternator DC to DC function while driving and the portable solar function while free camping, all in addition to the solar charging you already have.

T1 Terry

The first thing that I'd say is don't have too much faith in what the vendors of DC-DC charging systems tell you that you need. They are generally in the business of making money and not serving YOUR best interests.

My system is simple and has been more than we need for years. We have three 100Ah AGM batteries - one in the back of the car and two in the camper. The batteries are over 5 years old.

Big heavy cable (6 B&S minimum) from cranking battery to isolator with a cut out voltage of 12.7V. Big heavy cable from there to second battery in the back of the car and then to an Anderson plug. Perhaps the most important as it's the longest cable run is big heavy cable from the Anderson plug to the camper batteries. All of the big heavy cable is 6B&S MINIMUM. When camped we run a cable with Anderson plugs on both ends between the car and the camper. We have 120W of solar panel the controller for which plugs into another Anderson plug in the battery box.

Our usage is quite modest - a 40 litre Engel used as a fridge / freezer, lighting (LED) and sundry laptop and phone chargers. We also lug a small TV around as well.

For powered site use we have a home brew DC power supply at 13.9V that can supply 50A.

Using our setup we've never run out of power yet - not even during a February trip from the Latrobe Valley to Oodnadatta and beyond with a week long string of 40deg days.

Another consideration is that we have a 2000 Land Rover Discovery 2 which has a beefy and quite dumb alternator. The more modern "smart" alternators / regulators may well render our system inadequate.

All in all the main thing to bear in mind is to use the biggest cable you can lay your hands on and keep the runs as short as possible. Where possible use your chassis earth the reduce you total cable run by half. (No negative wire - return is via chassis).

A call to Traxide http://www.traxide.com.au/ may also be a good starting point even though he's in the business of making money he DOES offer good advice.

markf wrote:

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The first thing that I'd say is don't have too much faith in what the vendors of DC-DC charging systems tell you that you need. They are generally in the business of making money and not serving YOUR best interests.

My system is simple and has been more than we need for years. We have three 100Ah AGM batteries - one in the back of the car and two in the camper. The batteries are over 5 years old.

Big heavy cable (6 B&S minimum) from cranking battery to isolator with a cut out voltage of 12.7V. Big heavy cable from there to second battery in the back of the car and then to an Anderson plug. Perhaps the most important as it's the longest cable run is big heavy cable from the Anderson plug to the camper batteries. All of the big heavy cable is 6B&S MINIMUM. When camped we run a cable with Anderson plugs on both ends between the car and the camper. We have 120W of solar panel the controller for which plugs into another Anderson plug in the battery box.

Our usage is quite modest - a 40 litre Engel used as a fridge / freezer, lighting (LED) and sundry laptop and phone chargers. We also lug a small TV around as well.

For powered site use we have a home brew DC power supply at 13.9V that can supply 50A.

Using our setup we've never run out of power yet - not even during a February trip from the Latrobe Valley to Oodnadatta and beyond with a week long string of 40deg days.

Another consideration is that we have a 2000 Land Rover Discovery 2 which has a beefy and quite dumb alternator. The more modern "smart" alternators / regulators may well render our system inadequate.

All in all the main thing to bear in mind is to use the biggest cable you can lay your hands on and keep the runs as short as possible. Where possible use your chassis earth the reduce you total cable run by half. (No negative wire - return is via chassis).

A call to Traxide http://www.traxide.com.au/ may also be a good starting point even though he's in the business of making money he DOES offer good advice.

-- Edited by markf on Tuesday 25th of July 2017 07:01:41 PM

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 Whoa! A 50A home brew power supply at 13.9V?

Can you give us a bit more information?

markf wrote:

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The first thing that I'd say is don't have too much faith in what the vendors of DC-DC charging systems tell you that you need. They are generally in the business of making money and not serving YOUR best interests.

My system is simple and has been more than we need for years. We have three 100Ah AGM batteries - one in the back of the car and two in the camper. The batteries are over 5 years old.

Big heavy cable (6 B&S minimum) from cranking battery to isolator with a cut out voltage of 12.7V. Big heavy cable from there to second battery in the back of the car and then to an Anderson plug. Perhaps the most important as it's the longest cable run is big heavy cable from the Anderson plug to the camper batteries. All of the big heavy cable is 6B&S MINIMUM. When camped we run a cable with Anderson plugs on both ends between the car and the camper. We have 120W of solar panel the controller for which plugs into another Anderson plug in the battery box.

Our usage is quite modest - a 40 litre Engel used as a fridge / freezer, lighting (LED) and sundry laptop and phone chargers. We also lug a small TV around as well.

For powered site use we have a home brew DC power supply at 13.9V that can supply 50A.

Using our setup we've never run out of power yet - not even during a February trip from the Latrobe Valley to Oodnadatta and beyond with a week long string of 40deg days.

Another consideration is that we have a 2000 Land Rover Discovery 2 which has a beefy and quite dumb alternator. The more modern "smart" alternators / regulators may well render our system inadequate.

All in all the main thing to bear in mind is to use the biggest cable you can lay your hands on and keep the runs as short as possible. Where possible use your chassis earth the reduce you total cable run by half. (No negative wire - return is via chassis).

A call to Traxide http://www.traxide.com.au/ may also be a good starting point even though he's in the business of making money he DOES offer good advice.

-- Edited by markf on Tuesday 25th of July 2017 07:01:41 PM

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Hi Martin

Read Marks post carefully 

a nice post with Facts .

Yes ,many advising DC/Dc chargers either do not really understand the problem or are simply out to get as much money as they can from customer 

The correct step BEFORE looking at a DC/ DC charger is to use  a minimum of 6 B&S cable all the way from the vehcle alternator to the van battery AND if running a 3way fridge on 12V while driving , a seperate 6B&S feed from the vehicle alternator for it.

IF the vehicle has a smart alternator you MAY need to get it adjusted to boost it's output voltage. But the very clear message, as you have indicated,  IS GET THE CORRECT WIRING SET UP Before you spend money on  a Dc/Dc charger

, because the DC/ Dc charger itself requires heavy cables to perform correctly & should not be used to also supply an absorption type[ 3way fridge  fridge] 12V

It is designed to charge the battery

.Other heavy loads such as  a 3way fridge will give a false indication of battery state of charge & the fridge load may mean not much current is available for battery charging

The gent that you mentioned could also adjust the alternator IF needed

 If your panels already have a quality regulator  ,you will gain nothing by feeding the solar into the DC/Dc charger, just leave THAT as it is .

It will work happily with a DC / DC charger, IF you find you really do need one AFTER wiring as advised with heavy cables.

Bagmaker wrote:

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 Whoa! A 50A home brew power supply at 13.9V?

Can you give us a bit more information?

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 Made from junk box bits and pieces years ago for my radio habit. I managed to scrounge from somewhere a transformer with a 240V primary four 15V 15A secondaries. Just paralleled them up and used it in a circuit similar to http://www.eleccircuit.com/wp-content/uploads/2012/08/high-current-12v-30a-25a-20a-15a-power-supply.jpg with a few extra added stages. Works well, weighs a ton, produces heat, is crude, rude and disgusting but it works for me... Sometimes I even use it for the purpose that I originally built it for...

Just a bit of clarification to Peter's (Oldtrack) comment regarding cable size. The minimum cable size is 6 B&S or 13.5mmsq conductor cable, even for a DC to DC charger and heavier if the charger is a 40 amp unit and the alternator is low voltage output type or the caravan battery is at the rear of the caravan rather than the front boot. Hands on experience actually installing these things shows that a long cable run combined with a low voltage alternator requires up to 2 B&S cable or 33mmsq conductor to supply enough current at a high enough voltage on the input side for a 40 amp output DC to DC charger to output 40 amps. If the input voltage drops below 10.5v the DC to DC output will reduce, all to do with the current (amps) on the input side being too much for the gear in the charger, below 8.5v the charger will turn off and wait for the voltage to return to better than 12.6v. In real life installs I have had quite a few where the DC to DC charger was switching on/off due to the voltage drop at the end of the 6 B&S cable run. I had another where the battery was in the rear of the caravan and the owner rang to complain that the DC to DC charger had failed, same problem, the charger turning on/off. The fix on every occasion was to fit heavier cable, the result was a cooler running Dc to DC charger with full output.
What does all this also mean? To get 40 amps at the battery at a voltage high enough to recharge the battery anywhere near 90% SOC not only is heavy cable required but also a device to boost the voltage at the end of that long cable run. If you don't believe me, check the amps coming in on your battery monitor in the van after the house battery voltage is better than 12.6v while charging, I'll lay money that it won't be any where near 40 amps, by 13v I'll bet it's virtually non existent, how will this get the battery to the required 14.4v min required to end the boost charging cycle? Now also keep in mind the battery must reach this 14.4v to get to the absorption stage and that needs many hrs to get from the end of boost to close to fully charged. How many hrs do you plan to drive? Without some form of voltage boosting to improve the current flow (amps) into the battery it would require days not hrs to recharge a lead acid including the popular types of AGM battery to better than 80% SOC, you only have 30% of the capacity available then until that line in the sand of 50% SOC is reached. If you only ever use the top 25% of the battery capacity that means the charging process is starting with the battery already at 75%, alternator recharging with a some form of voltage booster would be an absolute waste of time, money and effort.
Ask anyone who originally had a direct cable charging system and the upgraded to a DC to DC charging system and see if they consider the DC to DC charger was a waste of money and effort?
The other thing I'd like to correct is running the 3 way fridge from the DC to DC charger, if it has a high enough output (amps) to supply the fridge as well as recharge the battery, why not use the money spent on a separate cable run for the fridge on heavier cabling and a better output or even double up on the DC to DC chargers.

One word of warning, many caravan builder install a cable from the fridge DC input that comes from the 12 pin plug to the house battery. Their logic is the excess current will also charge the battery, the reality is the house battery ends up powering the fridge, find this cable and disconnect it. The added problem is once a DC to DC charger is installed the house battery voltage is now higher than the incoming voltage from the 12 pin plug, so the current now flows backwards and back to the tow vehicle charging system. Not only is you precious solar now powering the vehicle electric rather than charging you house battery, the DC to DC charger is demanding to be supplied and this end up coming from the 12 pin plug circuit....... a dead loss loop that ends up burning out wires never designed to carry that much current.

T1 Terry

To illustrate Terry's point about cable size. Back in the day before I decided that my system was adequate I measured everything in sight. All of my cable runs are single wire (chassis -ve) 2G cable. With the camper batteries at 12V (~25% SOC) I measured a max of 50A at 14.0V at the isolator input AND output. At the batteries I only measured a MAX of 42A at 13.9V. All joints apart from the sliding contacts at the Anderson plug are correctly crimped. And yes, the Anderson plugs get warm to the touch so that'll be where the majority of losses occur. All chassis connections are properly crimped lugs welded to the chassis. In hindsight I went a bit overboard - must have been on an anti loss crusade I reckon... Either that or too much time on my hands...

That's with 2G cable which is considerably larger than 6 B&S so losses are considerably less.

When my current crop of AGM's start to kark it I'll go with LiFePo4 batteries which will doubtless open a whole new can of worms.