DC to DC charger in camper trailer

#1
Hi all

Just bought a camper trailer and want to set up an battery system in it. Our car has a dc-dc charger for our dual battery in the tray, can i use that for the trailer as well or do i need to fit another in the trailer and if i do fit one in the trailer, is it going to charge properly with 2 dc-dc chargers?

Thanks
 
#2
I Had the same setup, Redarc 1225 in the tub with120AH battery, I made an
anderson plug splitter and run a short lead to anderson plug on the towbar hooked up to the CT battery(120AH) via 8bs cable
it would charge both batterys and I had the added bonus of a backup battery if I left it connected to the ute in times of no solar power
the solar panel connected to the same anderson plug when it was used
everything worked well
I dont think you need a dc dc charger in the CT, however mine had a 240 volt charger to keep the battery alive when it was parked on the driveway or if you camped in a powered site
 
#3
I wouldn't bother with a DCDC in the camper trailer mate unless you have crappy cable runs. Use 8 b&s twin core cable and you will be right. I just use a VSR in my ute and it's been happily charging my aux and camper battery for years off the alternator. I have a 30 amp Victron battery charger in the CT for charging the batteries from mains power or the generator if the solar isn't happy due to weather but it's a pretty rare thing.

If it's decent weather my 200w panel with a victron mppt solar controller can keep my 2 fridges etc and charge both batteries without issue. No need to over think 12v stuff.
 
#4
I'm interested in this also. I have a battery in my camper already and it's charged by the main battery in the 4wd via fused 8bs anderson plug. Always wanted to know if i need a smart charger in the camper as well.
 
#7
Treat the camper as a separate entity to your current aux battery set up.

If your current dcdc charger operates as expected with no alternator related issues, duplicate the setup in the camper using suitable cabling (assuming the dcdc charger can handle camper battery bank and has solar input).

Depending on the existing current draws on your vehicle aux batteries and how much flexibility you want to build into the combo, consider a feed from vehicle aux to camper circuits. Make this feed switchable to take over when camper batteries get too low. You probably want to isolate your camper batteries and charging from their current draw too.
 
#9
I have a DC-DC in my camper and wouldn't be without it. Get a good one and you wont look back. Mine is a smart charger with 5 charge cycles, shows SOC, time till full, time till flat, draw rate, battery temp, it has MMPT solar input, 240v and 12v. Batteries are 8 years old and have been hammered on extended camping trips but are still nearly as good as new
 

cam04

Well-Known Member
#12
You’ll find (depending on the charger in the car) that you will charge slower when slaving the camper batteries off the existing system. The better way is to run an alternator feed straight to the trailer and put a second charger near the camper batteries, or none at all Depending on what type of alternator you have, how many batteries are in each, and if you want solar etc as well. There are multiple ways of getting a satisfactory outcome.
 
#13
How important is that? I have run mine down to mid 11's multiple times with no real adverse affect, maybe that is the big difference between running a good DC-DC and not just bulk chargeing from your alternator
AGM's if that is what you are using should not be taken past 50% depth of discharge for longevity as a rule, as it can significantly reduce cycle life meaning you get a lot less cycles from them. It has nothing to do with how they are being charged.

I would point out your alternator does not provide bulk charge voltage, they are setup to provide absorption rate voltage which is exactly want a DC-DC provides most of the time as they are generally current limited.

You’ll find (depending on the charger in the car) that you will charge slower when slaving the camper batteries off the existing system
This is very true, nothing charges batteries as fast as a VSR switched alternator feed as they allow 100+ amps to the batteries meaning the battery can take all the current it is rated for something a DC-DC generally can't do or can only do for the first battery.

If you think of it like this you have a Aux battery in your vehicle, you have one in you Camper Trailer and they are AGM's that will happily take 30-40amps each depending on brand. To have enough current available to charge your batteries to maximum effect you need 60-80 amps available, and that's just for 2 AGM's. It's only very recently that we are starting to see DC-DC's that can provide 40 amps total, a typical unit is 25 amps making them very current limited even for 1 battery let alone multiples.

Where DC-DC's really work is in area's with significant voltage drop due to under size cabling, and getting the last 10% of charge into the battery faster than a VSR. By nature our batteries are running fridges etc and have a pretty constant load so they will mostly stay in the absorption profile anyway. This is also why some manufacturers are including a "Smart Pass" option with their DC-DC product which is basically turning the DC-DC off and using a VSR where needed to overcome current limitations to maximum charging performance.

End of the day pick the solution that works for you, and your wallet. You can have 12v systems that cost 3k+ or ones that cost $800 and each can be as equally effective.
 
#14
AGM's if that is what you are using should not be taken past 50% depth of discharge for longevity as a rule, as it can significantly reduce cycle life meaning you get a lot less cycles from them. It has nothing to do with how they are being charged.

I would point out your alternator does not provide bulk charge voltage, they are setup to provide absorption rate voltage which is exactly want a DC-DC provides most of the time as they are generally current limited.



This is very true, nothing charges batteries as fast as a VSR switched alternator feed as they allow 100+ amps to the batteries meaning the battery can take all the current it is rated for something a DC-DC generally can't do or can only do for the first battery.

If you think of it like this you have a Aux battery in your vehicle, you have one in you Camper Trailer and they are AGM's that will happily take 30-40amps each depending on brand. To have enough current available to charge your batteries to maximum effect you need 60-80 amps available, and that's just for 2 AGM's. It's only very recently that we are starting to see DC-DC's that can provide 40 amps total, a typical unit is 25 amps making them very current limited even for 1 battery let alone multiples.

Where DC-DC's really work is in area's with significant voltage drop due to under size cabling, and getting the last 10% of charge into the battery faster than a VSR. By nature our batteries are running fridges etc and have a pretty constant load so they will mostly stay in the absorption profile anyway. This is also why some manufacturers are including a "Smart Pass" option with their DC-DC product which is basically turning the DC-DC off and using a VSR where needed to overcome current limitations to maximum charging performance.

End of the day pick the solution that works for you, and your wallet. You can have 12v systems that cost 3k+ or ones that cost $800 and each can be as equally effective.
Thank you for that, that was a great explanation for my truck driver brain. Much Appreciated.
 

Batts88

Well-Known Member
#15
AGM's if that is what you are using should not be taken past 50% depth of discharge for longevity as a rule, as it can significantly reduce cycle life meaning you get a lot less cycles from them. It has nothing to do with how they are being charged.

I would point out your alternator does not provide bulk charge voltage, they are setup to provide absorption rate voltage which is exactly want a DC-DC provides most of the time as they are generally current limited.



This is very true, nothing charges batteries as fast as a VSR switched alternator feed as they allow 100+ amps to the batteries meaning the battery can take all the current it is rated for something a DC-DC generally can't do or can only do for the first battery.

If you think of it like this you have a Aux battery in your vehicle, you have one in you Camper Trailer and they are AGM's that will happily take 30-40amps each depending on brand. To have enough current available to charge your batteries to maximum effect you need 60-80 amps available, and that's just for 2 AGM's. It's only very recently that we are starting to see DC-DC's that can provide 40 amps total, a typical unit is 25 amps making them very current limited even for 1 battery let alone multiples.

Where DC-DC's really work is in area's with significant voltage drop due to under size cabling, and getting the last 10% of charge into the battery faster than a VSR. By nature our batteries are running fridges etc and have a pretty constant load so they will mostly stay in the absorption profile anyway. This is also why some manufacturers are including a "Smart Pass" option with their DC-DC product which is basically turning the DC-DC off and using a VSR where needed to overcome current limitations to maximum charging performance.

End of the day pick the solution that works for you, and your wallet. You can have 12v systems that cost 3k+ or ones that cost $800 and each can be as equally effective.
In my wife's car I have an 85ah agm the manufacturers charging specs says max charge current 28amps does that mean it will only accept that amount when recharging and no more.

I also have 2 x 105ah agm batteries in my patrol charging via a Redarc 40amp BCDC charger it keeps them topped up fine you have to fit 60amp fuses for surge protection. On the Aussie battery site they say a 100ah battery will handle up to a 30amp charger and to base your charging rate at 30% of the batteries ah rating. If you use a smaller charger it will take longer but if you go too small it won't reach 100% full charge.
 
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#17
In my wife's car I have an 85ah agm the manufacturers charging specs says max charge current 28amps does that mean it will only accept that amount when recharging and no more.
That is exactly what that means.

I also have 2 x 105ah agm batteries in my patrol charging via a Redarc 40amp BCDC charger it keeps them topped up fine you have to fit 60amp fuses for surge protection. On the Aussie battery site they say a 100ah battery will handle up to a 30amp charger and to base your charging rate at 30% of the batteries ah rating. If you use a smaller charger it will take longer but if you go too small it won't reach 100% full charge.
Every battery has a C rating, or charge rating and it's a percentage expression of the capacity of the battery. For example a Fullriver AGM with a C rating of 0.40 means you can charge it at 40% of it's capacity, so if it's an 100AH battery it will take 40amps.

Your Redarc 40amp BCDC is therefore current limited, let's say you have lower grade 105ah with a c rating of 0.30 or 30% of capacity it means you're only providing them with with 20amps each say and they could take 31.5amps each. Meaning you are not charging them as fast as you could be, remember you don't push current the battery pulls what it wants, but if there aren't enough apples to go around they go hungry.

"fine" is a very subjective term and if you are happy with the performance that is awesome. However science and math say you're not getting the best out of your system.

DC-DC systems aren't designed to charge batteries at maximum performance, they are designed to overcome voltage loss from poor cable runs. They do this by swapping high current low voltage to low current high voltage, they are in essence a step up transformer.

Remember no one is saying they don't work, clearly they do but they are not fast and suit some applications better than other and some not well at all. However it's been my experience they are not needed once voltage drop is taken care of with decent cabling.

There are a lot of people with a vested interest is selling complex over the top 12v systems. The OP could spend a little or a lot with pretty much the same outcome.
 
#20
Fine meaning good etc the batteries get fully charge voltmeter usually sits any where from 12.8 - 13.1 both set ups also have fixed solar panels keeping them topped up.
I hope those numbers are not while the DCDC is in use? That's not even float voltage let alone absorption. It's hard to know what those numbers mean without some context, 12.8v is a good number if it's a rested battery with no load on it for at least a few hours as State of Charge cannot be measured properly with load on the battery.

Perhaps one less expensive option is to take the DC-DC from the vehicle (tray) to use with the camper (the advantage of the DC-DC being on long runs), then replace it in the vehicle with a VSR?
+1 This is a good idea, move the DCDC to the camper and let a VSR handle the vehicle.
 
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