I've read this article and I think I understand it. https://www.caravanworld.com.au/features/1509/dc-dc-battery-chargers-explained
However DC-DC chargers are not cheap. I have a 150W inverter (small can type) and a reasonable 60W charger. I'm hoping that combination will do same as a DC-DC charger. Is this OK?
Tony Bev said
08:47 PM Dec 27, 2017
I am not an Electrician
Not sure exactly what you mean, Rusty
If you are saying to put a 150 watt 240 volt inverter on to the battery, and then connect a 60 watt (5 amp) battery charger to the inverter to charge the battery
If it works then you have just made the breakthrough, in perpetual motion, we are all waiting for
Each time I have talked to an Electrician, they have been very adamant, that you can not produce more electricity, than the power being supplied to produce it
So I will stick my neck out here, and say no, it will not work, but I am unable to explain why, it will not work
Edit to say When I was experimenting with old batteries, (before I got my solar, and new batteries)
I have a 300 watt pure sine wave 12 volt to 240 volt inverter While charging my cordless drill, through its charger which said something like, 240 volts at 3 amps I noticed that there was about 8 amps going from the house/leisure battery to the 300 watt pure sine wave 12 volt to 240 volt inverter But do not quote me on the above numbers, as I am only going from memory I did make notes, but they are in a very, very, safe place, where no one will ever steal them
Edit again as I have just read Aus-Kiwi post
If your power going to the 150 watt 12 volt to 240 volt inverter, is coming from your vehicle engine battery, then I will not comment Except to mention, that a 240 volt power extension lead, going from a vehicle to a caravan, while travelling down the road, is a recipe for disaster, due to someone, (perhaps yourself) being electrocuted Also if you are going to use your engine battery (with engine running), at a camp, to power your 60 watt battery charger, then it would probably be cheaper, to use a generator
Hope that this makes sense
-- Edited by Tony Bev on Wednesday 27th of December 2017 09:00:35 PM
-- Edited by Tony Bev on Wednesday 27th of December 2017 09:10:20 PM
Aus-Kiwi said
08:53 PM Dec 27, 2017
MAYBE if inverter is in tug and using this to charge house batteries . My issue would be 240v through plug. Connector at tow bar etc . Low voltage (240v) doesnât have the same voltage drop issues over distance with smaller wire size . But irony want to open a can of warms !! Again !!
RustyD said
09:29 PM Dec 27, 2017
The inverter is plugged into a 12v source (tug or house). The battery charger is plugged into the inverter. My second spare battery is plugged into the charger. Im still wondering if I really need to dc-dc converter but when camping everyone is telling me I need an extra battery and a dc-dc converter in my ute and show me their setup. As I charge from either my tug (alternator) or solar (mppt controlled) I dont actually think I need one. Just checking that what I have is a compromise if I should need one.
Aus-Kiwi said
10:32 PM Dec 27, 2017
With that controller ? You should be fine . Keep the cable to extension battery large . 10mm sq Atleast !! 1v voltage drop line mits battery charge . Depends on regulator type on your tag ? Some drop off when main battery is charged to save economy .
dabbler said
12:04 AM Dec 28, 2017
Is your inverter pure sine wave ? All the can type ones I looked at are modified sine wave. Your 60w charger will probably require pure sine wave. There are cheap dc-dc chargers around so I would start looking rather than attempt to jury-rig a lousy 5A ac-dc charger.
RustyD said
11:08 AM Dec 28, 2017
dabbler wrote:
Is your inverter pure sine wave ? All the can type ones I looked at are modified sine wave. Your 60w charger will probably require pure sine wave. There are cheap dc-dc chargers around so I would start looking rather than attempt to jury-rig a lousy 5A ac-dc charger.
Thanks Dabbler. You reply implies to me that it ain't worth the effort or risk.
Tony Bev said
11:32 AM Dec 28, 2017
The main reason for my DC/DC engine/solar charger, was that when I had a 3 way fridge (running on gas), I liked to park in the shade, to help the fridge work, which meant that the roof solar was not working
Plus the house/leisure batteries are still being charged when travelling on overcast days
Now that I have a 12 volt compressor fridge, the DC/DC charger is not an essential item, as I do not need to continually park in the shade
Aus-Kiwi said
12:01 PM Dec 28, 2017
Have to say fitting a compressor fridge IS the best thing we did . Just for Secuity and a little self confidence we added extra solar which is cheap enough imo these days especially if you fit them yourself .. 3 way fridge is more for weekender type . If your going away for weeks at a time the compressor type is streets a head . Technology with rotory or low amp high efficiency compressors way better . If you have room ? The $400 for DC to DC can be spent on extra solar ..There is a place for them depending on your options and charging system up front .
swamp said
06:07 PM Dec 28, 2017
HI
Rusty D
Unless u have very low power draw on your House batteries . But having 2 says u donot
Charging systems work as a WHOLE .. Recharge at a slow/low level is ok if u are not drawing to much power to start with.
System consumption audit for free camping ability NOT C/PARKS
Do u only run leds and or compressor fridge , charging TV Radio etc etc
This will determine your battery AH
Most people 240AH
Then u must recharge 50% use capacity eg 120ah
Average PSH per day summer winter 5.5hrs
There is solar production either side of PSH but production is unreliable
200watts around 48ah production x2 in 24 hrs
DC--DC charging
Direct altenator connect is 25mmsq cable [ .4 volt drop ] at 35amps ,ideallycurrenet at spec volt drop . Battery will only use what it needs anyway .
THE BIGGEST ISSUE WITH DIRECT CONNECT IS SIZE OF CABLE .
If volts are below 14.oo charging time can triple
dc /dc charger 25amps or greater depending upon batt bank size . Most have MPPT controllers inbuilt.
So 1 hour driving will output 25amp etc
T1 Terry said
02:23 PM Dec 29, 2017
RustyD wrote:
The inverter is plugged into a 12v source (tug or house). The battery charger is plugged into the inverter. My second spare battery is plugged into the charger. Im still wondering if I really need to dc-dc converter but when camping everyone is telling me I need an extra battery and a dc-dc converter in my ute and show me their setup. As I charge from either my tug (alternator) or solar (mppt controlled) I dont actually think I need one. Just checking that what I have is a compromise if I should need one.
The charger is a 60w charger and not a 60 amp charger? A 60 amp charger would require at least a 1000w inverter and it would need to be pure sine wave.
I'm not sure why you have a spare battery, but if you want to fast charge the last bit into that because it is used as boat battery for a trolling motor then this is one option, but not a very efficient one.
Next, the inverter being modified sign wave will work ok with all but the really high end smart chargers and I doubt very much a 5 amp charger comes into that category.
Next but not least, if you want to charge from the tug battery while driving the inverter will need to be at the end of decent gauge cable running back to the van and then the charger plugged into that, but for 5 amps output I can't see the value to be honest. Most DC to DC charger are a minimum 20 amps, the norm 25 amps to 30 amps and the bigger unit 40 amps to 50 amps, so 5 amps is not going to charge a battery in a few hrs, more like 12 hrs to 24 hrs and that is a big ask from a house battery via such an inefficient charging system.
T1 Terry
Muddy said
09:51 AM Jan 16, 2018
There is another reason to go to a BCDC charger in your van.
Most modern tugs do not produce sufficient voltage to charge your van battery while towing. Once my Cranking battery is fully charged my smart alternator drops its output voltage to 12.6V. By the time this gets back to my van battery it will be lower than this
Volt drop = Resistivity of material (normally copper so look this up) X length of cable All divided by the cross sectional area of the cable.
This will not get even close to adding any half decent charge to my battery. I have purchased a BCDC LOW VOLTAGE 40 Amp Redarc charger for just under $400 (Frankies Auto Electrics , South Nowra NSW) and installed (Luckily for free apart from the costs of the terminals heat shrink etc). This unit accepts the low Voltage from the tug and ramps it up to 13.8V for charging and floating the battery. It also incorporates a decent MPPT regulator for solar panel input which works well for me as I use a mobile folding panel. Another benefit is that it is soldered joint connected and Lug terminal connected to my battery so I know will not vibrate free at any time.
Just bear in mind that the charger should be fitted as close as possible to the van battery NOT in the car! A good buddy of mine proudly showed me his charger fitted to the car so that it could also be used to charge an aux battery and I had to tell him that this would not work for the van as the volts produced by the charger would be insufficient to charge the van battery.
The way I see it is no matter whether on the tow or stationary, if you are using the cars alternator to charge a battery through inverters and then a charger, then the losses plus volt drop due to cable lengths will simply not do as good a job as a permanently mounted BCDC charger. (IMO)
I've read this article and I think I understand it. https://www.caravanworld.com.au/features/1509/dc-dc-battery-chargers-explained
However DC-DC chargers are not cheap. I have a 150W inverter (small can type) and a reasonable 60W charger. I'm hoping that combination will do same as a DC-DC charger. Is this OK?
I am not an Electrician
Not sure exactly what you mean, Rusty
If you are saying to put a 150 watt 240 volt inverter on to the battery, and then connect a 60 watt (5 amp) battery charger to the inverter to charge the battery
If it works then you have just made the breakthrough, in perpetual motion, we are all waiting for
Each time I have talked to an Electrician, they have been very adamant, that you can not produce more electricity, than the power being supplied to produce it
So I will stick my neck out here, and say no, it will not work, but I am unable to explain why, it will not work
Edit to say
When I was experimenting with old batteries, (before I got my solar, and new batteries)
I have a 300 watt pure sine wave 12 volt to 240 volt inverter
While charging my cordless drill, through its charger which said something like, 240 volts at 3 amps
I noticed that there was about 8 amps going from the house/leisure battery to the 300 watt pure sine wave 12 volt to 240 volt inverter
But do not quote me on the above numbers, as I am only going from memory
I did make notes, but they are in a very, very, safe place, where no one will ever steal them
Edit again as I have just read Aus-Kiwi post
If your power going to the 150 watt 12 volt to 240 volt inverter, is coming from your vehicle engine battery, then I will not comment
Except to mention, that a 240 volt power extension lead, going from a vehicle to a caravan, while travelling down the road, is a recipe for disaster, due to someone, (perhaps yourself) being electrocuted
Also if you are going to use your engine battery (with engine running), at a camp, to power your 60 watt battery charger, then it would probably be cheaper, to use a generator
Hope that this makes sense
-- Edited by Tony Bev on Wednesday 27th of December 2017 09:00:35 PM
-- Edited by Tony Bev on Wednesday 27th of December 2017 09:10:20 PM
Thanks Dabbler. You reply implies to me that it ain't worth the effort or risk.
Plus the house/leisure batteries are still being charged when travelling on overcast days
Now that I have a 12 volt compressor fridge, the DC/DC charger is not an essential item, as I do not need to continually park in the shade
Rusty D
Unless u have very low power draw on your House batteries . But having 2 says u donot
Charging systems work as a WHOLE .. Recharge at a slow/low level is ok if u are not drawing to much power to start with.
System consumption audit for free camping ability NOT C/PARKS
Do u only run leds and or compressor fridge , charging TV Radio etc etc
This will determine your battery AH
Most people 240AH
Then u must recharge 50% use capacity eg 120ah
Average PSH per day summer winter 5.5hrs
There is solar production either side of PSH but production is unreliable
200watts around 48ah production x2 in 24 hrs
DC--DC charging
Direct altenator connect is 25mmsq cable [ .4 volt drop ] at 35amps ,ideallycurrenet at spec volt drop . Battery will only use what it needs anyway .
THE BIGGEST ISSUE WITH DIRECT CONNECT IS SIZE OF CABLE .
If volts are below 14.oo charging time can triple
dc /dc charger 25amps or greater depending upon batt bank size . Most have MPPT controllers inbuilt.
So 1 hour driving will output 25amp etc
The charger is a 60w charger and not a 60 amp charger? A 60 amp charger would require at least a 1000w inverter and it would need to be pure sine wave.
I'm not sure why you have a spare battery, but if you want to fast charge the last bit into that because it is used as boat battery for a trolling motor then this is one option, but not a very efficient one.
Next, the inverter being modified sign wave will work ok with all but the really high end smart chargers and I doubt very much a 5 amp charger comes into that category.
Next but not least, if you want to charge from the tug battery while driving the inverter will need to be at the end of decent gauge cable running back to the van and then the charger plugged into that, but for 5 amps output I can't see the value to be honest. Most DC to DC charger are a minimum 20 amps, the norm 25 amps to 30 amps and the bigger unit 40 amps to 50 amps, so 5 amps is not going to charge a battery in a few hrs, more like 12 hrs to 24 hrs and that is a big ask from a house battery via such an inefficient charging system.
T1 Terry
Most modern tugs do not produce sufficient voltage to charge your van battery while towing. Once my Cranking battery is fully charged my smart alternator drops its output voltage to 12.6V. By the time this gets back to my van battery it will be lower than this
Volt drop = Resistivity of material (normally copper so look this up) X length of cable All divided by the cross sectional area of the cable.
This will not get even close to adding any half decent charge to my battery. I have purchased a BCDC LOW VOLTAGE 40 Amp Redarc charger for just under $400 (Frankies Auto Electrics , South Nowra NSW) and installed (Luckily for free apart from the costs of the terminals heat shrink etc). This unit accepts the low Voltage from the tug and ramps it up to 13.8V for charging and floating the battery. It also incorporates a decent MPPT regulator for solar panel input which works well for me as I use a mobile folding panel. Another benefit is that it is soldered joint connected and Lug terminal connected to my battery so I know will not vibrate free at any time.
Just bear in mind that the charger should be fitted as close as possible to the van battery NOT in the car! A good buddy of mine proudly showed me his charger fitted to the car so that it could also be used to charge an aux battery and I had to tell him that this would not work for the van as the volts produced by the charger would be insufficient to charge the van battery.
The way I see it is no matter whether on the tow or stationary, if you are using the cars alternator to charge a battery through inverters and then a charger, then the losses plus volt drop due to cable lengths will simply not do as good a job as a permanently mounted BCDC charger. (IMO)