What are some of the reasons to have a DC to DC charger?
Aussie Paul.
Peter_n_Margaret said
02:33 PM Oct 26, 2019
Too much voltage drop from the car to the van.
Cheers,
Peter
dabbler said
03:30 PM Oct 26, 2019
Multistage charging over different battery chemistries. Integrated solar input and regulation. Potential for improved monitoring.
Noelpolar said
09:58 PM Oct 26, 2019
Isolation.... say lithium aux and lead acid starter.
Ziggy99 said
04:22 AM Oct 28, 2019
The alternator alone doesn't fully charge your batteries by a good margin, so you're not getting the capacity you paid for and their life is shortened.
denmonkey said
01:11 PM Oct 29, 2019
then yu can tell everyone you have one :)
Whenarewethere said
01:47 PM Oct 29, 2019
Smart alternator
aussie_paul said
02:16 PM Oct 29, 2019
denmonkey wrote:
then yu can tell everyone you have one :)
Ha ha, lol.
Aussie Paul.
T1 Terry said
04:30 PM Oct 29, 2019
denmonkey wrote:
then yu can tell everyone you have one :)
and the winner is ....... :lol:
T1 Terry
Sarge9 said
09:42 PM Oct 29, 2019
It seem to be a relevant question. And bragging rights seem to be the common answer. I have no expertise. But with my Colorado putting out 14.2 fairly constantly and down to 13.0 as day wears on, I can't see how a DC to DC charger could improve on that. If the tug has an older style simple Alternator with a flat 13 or less out put then may be the DC to DC can do some magic. Or am I just piddling in the wind again. And in any case my prefered supplier of things battery and solar..... Blue Apple Solar.... said no, don't waste ya money. When I explained what i was doing, what i had read . They were not going to sell me one.
Good luck. Sarge.
-- Edited by Sarge9 on Tuesday 29th of October 2019 09:43:51 PM
Moose2 said
06:52 AM Oct 30, 2019
Sarge9 wrote:
And in any case my prefered supplier of things battery and solar..... Blue Apple Solar.... said no, don't waste ya money. When I explained what i was doing, what i had read . They were not going to sell me one.
Good luck. Sarge.
-- Edited by Sarge9 on Tuesday 29th of October 2019 09:43:51 PM
Wow...good to see some companies still have high standards and don't just chase the $s.
aussie_paul said
11:20 AM Oct 30, 2019
Last weekend I had a mate visit as we hadn't caught up since August last year and he had a new grandchild to visit. He also lives 5 hours drive away.
He is an auto electrician so I was asking his views on my DC to DC van charger. He just couldn't understand why I had a DC to DC charger for my situation. My tests this last week have proven to me that he was right. Just something else to possibly fail. Perhaps it would produce a few extra amps while driving, BUT to me though, not worth effort. Correct cabling is paramount to success in there situations.
Aussie Paul.
T1 Terry said
12:00 PM Oct 30, 2019
Sarge9 wrote:
It seem to be a relevant question. And bragging rights seem to be the common answer. I have no expertise. But with my Colorado putting out 14.2 fairly constantly and down to 13.0 as day wears on, I can't see how a DC to DC charger could improve on that. If the tug has an older style simple Alternator with a flat 13 or less out put then may be the DC to DC can do some magic. Or am I just piddling in the wind again. And in any case my prefered supplier of things battery and solar..... Blue Apple Solar.... said no, don't waste ya money. When I explained what i was doing, what i had read . They were not going to sell me one.
Good luck. Sarge.
-- Edited by Sarge9 on Tuesday 29th of October 2019 09:43:51 PM
How about I try the maths approach to assist in deciding if a DC to DC charger could be an advantage or just a $$ grabbing gimmick.
First we will use the 14.2v start battery charging as can be found in the early non computer controlled everything vehicles. A basic alternator with either an internal or external regulator.
Basic model, start battery and alternator are at the front of the tow vehicle. A cable is run from the start battery to a fuse and then on to the towbar and an Anderson plug, we will ignore the VSR or solenoid for this simplified example, don't do this in your install unless you are willing to unplug the Anderson plug each time you stop to avoid draining the start battery.
Next we have the draw bar on the caravan with the Anderson plug and cable that runs back to the house battery. We will add a fuse in here as well because we would be messing with a disaster with the house battery being the power source for a short any where along the cable back to the start battery fuse. At 14.2v from the start battery we could use 6 B&S cable (13.5mm sq) as this is rated to a safe maximum of 125 amps, we will fit a 100 amp fuse at each end. For the sake of numbers, let's say the alternator can handle a continuous output of 140 amps, rare but it doesn't matter for this example.
Length of cable from the start battery to the towbar allowing for the extra bit to follow a safe path so the cable will avoid being damaged, 10 mtrs say.
Now the caravan draw bar to the house battery, mid mounted, 7 mtrs? Total 17 mtrs of cable, 2 fuses, 2 Anderson plugs and 8 crimp lugs on the positive cable ( battery terminal, fuse in, fuse out, Anderson plug, van Anderson plug, fuse in, fuse out, house battery.) and 4 on the negative, (start battery, Anderson plug, van Anderson plug, house battery) a total of 12 crimp joints. This is important to keep in mind because every joint adds resistance, very little for a really good joint but it can be a lot with a poor joint.
How much battery charging are we expecting, we have a 140 amp alternator after all, let's be gentle and aim for 40 amps the same as the bigger DC to DC chargers can deliver.
So the sum is, 40 amps @ 14.2v over 17 mtrs plus the joints, add what ever number of mtrs you think applicable but we will say every joint is perfect in our perfect world. Feed this into an on line calculator https://www.youtube.com/watch?v=Mvy3g_NIr8s&list=PL2l32K1w0jp-m04Jl-3PHmtapevOuCeIp&index=21&t=0s conductor is copper, cable AWG is 6 (B&S and AWG are close enough to the same for this example) 14vdc, DC voltage, 1 conductor pair, 17 mtrs cable length and 40 amps is what we want to come out the other end, press the magic button and it tells us that 14.2v at 40 amps in one end will come out as 12.4v at 40 amps at the other end.
12.4v will not fully recharge a battery that was only drained to 50% SOC, 12vdc At 50% SOC means there is only 0.4v difference between what is coming in and what is already there .... 40 amps will not flow into a lead acid battery with only a 0.4v difference. If you doubt that statement, try it with a set of jumper leads between a battery at 12.4v and a second battery at 12v, and this is only a few meters of cable.
To even achieve a float voltage at the house battery we have to reduce the current (amps) we expect to see travel through the cable
Back to the on line calculator and we can start reducing the amps till we see 13.8v come out the other end, at 8 amps we can get 13.85vdc out of the other end.
If you have a 100Ah AGM battery discharged to 50% SOC, you need to put back more than the 50 amps you took out to cover the internal losses, being generous we will say 10% (really around 20%) so we need 55 Ah and we have an 8 amp charger, it will take around 9 hrs driving if the battery would accept the full 8 amps right up to 100% SOC and there was nothing else running in the caravan, that includes the fridge.
Not going to happen is it .... do the sums if you have a bigger battery bank, now add in a solar regulator as well, it will try to get the battery up to 14.4v before dropping back to the 13.8v float charge, as soon as the voltage reaches 14.1v in the house battery, less than 1 amp will flow down from the alternator .... all the charging will now be solar charging.
Add a DC to DC charger at the house battery end, we want 40 amps at 14.4v max ready to charge the house battery to get it recharged as quick as possible, 40 x 14.4v = 580w output, add 10% for the losses through the DC to DC charger and we now need around 650w.
Let's go back to the first run through the on line calculator, 40 amp @ 14.2v one end comes out as 40 amps @ 12.44v at the other end. 40 x 12.44v = roughly 500w, but we need 650w going into the DC to DC charger to get the 40 amps @ 14.4v out the other end .... more amps required.
55 amp x 11.78v = 647.9w, close enough for our 650w input requirement. (run the 55 amps through the on line calculator and 11.78v is the result)
This all hinges on there being a constant 14.2v at the start battery and there is zero resistance through all those crimp, bolted joints, fuses and Anderson plug connections.
A long read I know, but does it make any more sense now?
T1 Terry
Noelpolar said
08:39 PM Oct 30, 2019
In my case.... my run is 13.5m in length from vehicle battery to van battery location.... after 10 minutes or so of vehicle warming up..... then 13.2 or so volts is best I get at my source..... even with 25mm2 cable my van battery will only see 12.5v if some how 40amps was to flow.... which.... without a DC2DC.... it won't.
aussie_paul said
09:51 PM Oct 30, 2019
Thanks Terry. Vehicle charging is only one part of the system, we have solar and a 240v charger that puts out 40 amps to the batteries whilst the genset is running for microwave and/or coffee machine.
I will be watching things closely and with interest when we head to Portland on the 19th Nov. It will be the first time with all good batteries, solar, vehicle charging, and the 40 amp AC charger.
Aussie Paul.
Marken said
01:12 AM Nov 3, 2019
Hi Guys.
I know that this isn't a reply as such but I am seeking suggestions about the validity of using a DC/DC charger to charge the 2 x 130AH house batteries in my caravan. The reasons for this are that we plan to do some extensive travelling, mainly free camping for overnights which will not allow for much solar charging when stopped (even if it is available). Running the 3-way fridge off the batteries means they will have to be kept topped up en- route.
I propose to install the DC/DC charger (CTEK 250SA + Smartpass) in the back of my Prado 150 then feed out to an Anderson plug at the tow point. From there a connection to my house batteries which are about 1 metre apart.
I know that, ideally, the DC/DC charger should be as close to the batteries as possible so as to reduce voltage drop and enable temperature monitoring but well ventilated space near the batteries is VERY limited and the units will not fit.
I propose to use 25mm2 cable for the long runs (Starter battery to DC/DC charger +ve only, chassis for ve and from A-frame to batteries) and more flexible 4B&S for the short runs (in and out of the charger, Anderson plugs to fixed point on A-frame).
Fuses will be fitted just out of starter battery, just out of charger and just before house batteries. These will all be 120Amp breakers. The Anderson plug will also be 120Amp.
I already have the 25mm2 cable which is double insulated and I already have the CTEK bits so cost from here is negligible.
I would love to get some feedback on my proposal and any suggestions please.
Whenarewethere said
04:59 PM Nov 3, 2019
It's not clear how far it actually is from the DC-DC charger to the batteries.
Marken said
03:47 PM Nov 4, 2019
Whenarewethere wrote:
It's not clear how far it actually is from the DC-DC charger to the batteries.
From the DC/DC charger to the batteries it will be 3 - 3.5 Metres.
About half of this will be in 4B&S and the remainder will be in 25mm2.
With one 120A Anderson plug in between
-- Edited by Marken on Tuesday 5th of November 2019 11:15:54 AM
T1 Terry said
05:25 PM Nov 4, 2019
Run the negative cables from the start battery to the DC to DC charger and from the DC to DC charger to the Anderson plug. On the caravan run the negative cable from the Anderson plug to the battery terminal. Using chassis earth links causes more grief in RV electrics than just about any other problem due to the poor contact that often occurs between the cable terminal and the metal chassis surface. These rust or oxidise quickly due to current passing through dissimilar metals and this creates voltage drop.
The cable from the DC to DC through to the house battery sound good enough to carry the current, split the power to the 3 way fridge away from the house battery cable at the Anderson plug but be sure to switch the fridge over to gas as soon as you stop, or better still, use a fridge switch that is virtually a motion sensor that will disconnect the battery power from the fridge 10 mins after you stop moving. I would recommend fitting one of these au.rs-online.com/web/p/rectifier-diodes-schottky-diodes/4859604/ on a heatsink close to the battery on that DC to DC cable to stop the 3 way fridge from trying to use the house battery to power it rather than from the DC to DC charger.
As far as the "Smart Pass" it will be interesting to see how that goes for you. The theory is good, but within 10 mins of the DC to DC running the smart pass doesn't seem to pass much current at all from the tests we have done. Might work better for deeply discharged lead acid batteries, we only work with lithium batteries so all the tests involved recharging lithium batteries and not lead acid batteries.
The only other thing, how much current will the 3 way fridge draw? Just wondering if there will be enough left from the 25 amps from the DC to DC to charge the battery.
T1 Terry
Whenarewethere said
05:28 PM Nov 4, 2019
So 7 metres there & back ( + & - ) at 20amp, if it is all 4awg 0.1164 voltage drop.
2awg -0.0732
4awg -0.1164
6awg -0.1848
8awg -0.2940
So if you can use 4awg as much as possible you will have very minimal voltage loss.
4awg Jaycar cable into 50amp plug to reduce voltage loss!
Hi Guys
Many thanks for the advice. This is exactly what I was looking for.
Noting that the -ve connection (Batt to DC/DC) should be cable rather than chassis conflicts with local "Battery expert" but I understand your reasoning, No probs with that as I have heaps of 25mm2 cable. Just passing two of them around bends will be diffficult.
I will check on the 3-way fridge consumption. I think I have a 15amp fuse in there but will check.
I looked at the Diode assembly but not really sure how it shold be connected. Maybe will go with the "fridge switch" as that seems more understandable.
Regards
T1 Terry said
03:27 PM Nov 5, 2019
The diode block is an opposing pair, so the positive passes through one way but can't return and the negative passes through the opposite way via the other diode. Similar to a non return valve for water, the current can flow in but not back out, so unless the DC to DC charger is supplying power to the fridge, it doesn't get any because the diodes (one way valves) stop the current coming back up the cable and then to the fridge.
What are some of the reasons to have a DC to DC charger?
Aussie Paul.
Cheers,
Peter
Smart alternator
Ha ha, lol.
Aussie Paul.
and the winner is ....... :lol:
T1 Terry
It seem to be a relevant question. And bragging rights seem to be the common answer.
I have no expertise. But with my Colorado putting out 14.2 fairly constantly and down to 13.0 as day wears on, I can't see how a DC to DC charger could improve on that. If the tug has an older style simple Alternator with a flat 13 or less out put then may be the DC to DC can do some magic. Or am I just piddling in the wind again. And in any case my prefered supplier of things battery and solar..... Blue Apple Solar.... said no, don't waste ya money. When I explained what i was doing, what i had read . They were not going to sell me one.
Good luck.
Sarge.
-- Edited by Sarge9 on Tuesday 29th of October 2019 09:43:51 PM
Wow...good to see some companies still have high standards and don't just chase the $s.
Last weekend I had a mate visit as we hadn't caught up since August last year and he had a new grandchild to visit. He also lives 5 hours drive away.
He is an auto electrician so I was asking his views on my DC to DC van charger. He just couldn't understand why I had a DC to DC charger for my situation. My tests this last week have proven to me that he was right. Just something else to possibly fail. Perhaps it would produce a few extra amps while driving, BUT to me though, not worth effort. Correct cabling is paramount to success in there situations.
Aussie Paul.
How about I try the maths approach to assist in deciding if a DC to DC charger could be an advantage or just a $$ grabbing gimmick.
First we will use the 14.2v start battery charging as can be found in the early non computer controlled everything vehicles. A basic alternator with either an internal or external regulator.
Basic model, start battery and alternator are at the front of the tow vehicle. A cable is run from the start battery to a fuse and then on to the towbar and an Anderson plug, we will ignore the VSR or solenoid for this simplified example, don't do this in your install unless you are willing to unplug the Anderson plug each time you stop to avoid draining the start battery.
Next we have the draw bar on the caravan with the Anderson plug and cable that runs back to the house battery. We will add a fuse in here as well because we would be messing with a disaster with the house battery being the power source for a short any where along the cable back to the start battery fuse. At 14.2v from the start battery we could use 6 B&S cable (13.5mm sq) as this is rated to a safe maximum of 125 amps, we will fit a 100 amp fuse at each end. For the sake of numbers, let's say the alternator can handle a continuous output of 140 amps, rare but it doesn't matter for this example.
Length of cable from the start battery to the towbar allowing for the extra bit to follow a safe path so the cable will avoid being damaged, 10 mtrs say.
Now the caravan draw bar to the house battery, mid mounted, 7 mtrs? Total 17 mtrs of cable, 2 fuses, 2 Anderson plugs and 8 crimp lugs on the positive cable ( battery terminal, fuse in, fuse out, Anderson plug, van Anderson plug, fuse in, fuse out, house battery.) and 4 on the negative, (start battery, Anderson plug, van Anderson plug, house battery) a total of 12 crimp joints. This is important to keep in mind because every joint adds resistance, very little for a really good joint but it can be a lot with a poor joint.
How much battery charging are we expecting, we have a 140 amp alternator after all, let's be gentle and aim for 40 amps the same as the bigger DC to DC chargers can deliver.
So the sum is, 40 amps @ 14.2v over 17 mtrs plus the joints, add what ever number of mtrs you think applicable but we will say every joint is perfect in our perfect world. Feed this into an on line calculator https://www.youtube.com/watch?v=Mvy3g_NIr8s&list=PL2l32K1w0jp-m04Jl-3PHmtapevOuCeIp&index=21&t=0s conductor is copper, cable AWG is 6 (B&S and AWG are close enough to the same for this example) 14vdc, DC voltage, 1 conductor pair, 17 mtrs cable length and 40 amps is what we want to come out the other end, press the magic button and it tells us that 14.2v at 40 amps in one end will come out as 12.4v at 40 amps at the other end.
12.4v will not fully recharge a battery that was only drained to 50% SOC, 12vdc At 50% SOC means there is only 0.4v difference between what is coming in and what is already there .... 40 amps will not flow into a lead acid battery with only a 0.4v difference. If you doubt that statement, try it with a set of jumper leads between a battery at 12.4v and a second battery at 12v, and this is only a few meters of cable.
To even achieve a float voltage at the house battery we have to reduce the current (amps) we expect to see travel through the cable
Back to the on line calculator and we can start reducing the amps till we see 13.8v come out the other end, at 8 amps we can get 13.85vdc out of the other end.
If you have a 100Ah AGM battery discharged to 50% SOC, you need to put back more than the 50 amps you took out to cover the internal losses, being generous we will say 10% (really around 20%) so we need 55 Ah and we have an 8 amp charger, it will take around 9 hrs driving if the battery would accept the full 8 amps right up to 100% SOC and there was nothing else running in the caravan, that includes the fridge.
Not going to happen is it .... do the sums if you have a bigger battery bank, now add in a solar regulator as well, it will try to get the battery up to 14.4v before dropping back to the 13.8v float charge, as soon as the voltage reaches 14.1v in the house battery, less than 1 amp will flow down from the alternator .... all the charging will now be solar charging.
Add a DC to DC charger at the house battery end, we want 40 amps at 14.4v max ready to charge the house battery to get it recharged as quick as possible, 40 x 14.4v = 580w output, add 10% for the losses through the DC to DC charger and we now need around 650w.
Let's go back to the first run through the on line calculator, 40 amp @ 14.2v one end comes out as 40 amps @ 12.44v at the other end. 40 x 12.44v = roughly 500w, but we need 650w going into the DC to DC charger to get the 40 amps @ 14.4v out the other end .... more amps required.
55 amp x 11.78v = 647.9w, close enough for our 650w input requirement. (run the 55 amps through the on line calculator and 11.78v is the result)
This all hinges on there being a constant 14.2v at the start battery and there is zero resistance through all those crimp, bolted joints, fuses and Anderson plug connections.
A long read I know, but does it make any more sense now?
T1 Terry
Thanks Terry. Vehicle charging is only one part of the system, we have solar and a 240v charger that puts out 40 amps to the batteries whilst the genset is running for microwave and/or coffee machine.
I will be watching things closely and with interest when we head to Portland on the 19th Nov. It will be the first time with all good batteries, solar, vehicle charging, and the 40 amp AC charger.
Aussie Paul.
I know that this isn't a reply as such but I am seeking suggestions about the validity of using a DC/DC charger to charge the 2 x 130AH house batteries in my caravan. The reasons for this are that we plan to do some extensive travelling, mainly free camping for overnights which will not allow for much solar charging when stopped (even if it is available). Running the 3-way fridge off the batteries means they will have to be kept topped up en- route.
I propose to install the DC/DC charger (CTEK 250SA + Smartpass) in the back of my Prado 150 then feed out to an Anderson plug at the tow point. From there a connection to my house batteries which are about 1 metre apart.
I know that, ideally, the DC/DC charger should be as close to the batteries as possible so as to reduce voltage drop and enable temperature monitoring but well ventilated space near the batteries is VERY limited and the units will not fit.
I propose to use 25mm2 cable for the long runs (Starter battery to DC/DC charger +ve only, chassis for ve and from A-frame to batteries) and more flexible 4B&S for the short runs (in and out of the charger, Anderson plugs to fixed point on A-frame).
Fuses will be fitted just out of starter battery, just out of charger and just before house batteries. These will all be 120Amp breakers. The Anderson plug will also be 120Amp.
I already have the 25mm2 cable which is double insulated and I already have the CTEK bits so cost from here is negligible.
I would love to get some feedback on my proposal and any suggestions please.
It's not clear how far it actually is from the DC-DC charger to the batteries.
From the DC/DC charger to the batteries it will be 3 - 3.5 Metres.
About half of this will be in 4B&S and the remainder will be in 25mm2.
With one 120A Anderson plug in between
-- Edited by Marken on Tuesday 5th of November 2019 11:15:54 AM
The cable from the DC to DC through to the house battery sound good enough to carry the current, split the power to the 3 way fridge away from the house battery cable at the Anderson plug but be sure to switch the fridge over to gas as soon as you stop, or better still, use a fridge switch that is virtually a motion sensor that will disconnect the battery power from the fridge 10 mins after you stop moving. I would recommend fitting one of these au.rs-online.com/web/p/rectifier-diodes-schottky-diodes/4859604/ on a heatsink close to the battery on that DC to DC cable to stop the 3 way fridge from trying to use the house battery to power it rather than from the DC to DC charger.
As far as the "Smart Pass" it will be interesting to see how that goes for you. The theory is good, but within 10 mins of the DC to DC running the smart pass doesn't seem to pass much current at all from the tests we have done. Might work better for deeply discharged lead acid batteries, we only work with lithium batteries so all the tests involved recharging lithium batteries and not lead acid batteries.
The only other thing, how much current will the 3 way fridge draw? Just wondering if there will be enough left from the 25 amps from the DC to DC to charge the battery.
T1 Terry
So 7 metres there & back ( + & - ) at 20amp, if it is all 4awg 0.1164 voltage drop.
2awg -0.0732
4awg -0.1164
6awg -0.1848
8awg -0.2940
So if you can use 4awg as much as possible you will have very minimal voltage loss.
4awg Jaycar cable into 50amp plug to reduce voltage loss!
Many thanks for the advice. This is exactly what I was looking for.
Noting that the -ve connection (Batt to DC/DC) should be cable rather than chassis conflicts with local "Battery expert" but I understand your reasoning, No probs with that as I have heaps of 25mm2 cable. Just passing two of them around bends will be diffficult.
I will check on the 3-way fridge consumption. I think I have a 15amp fuse in there but will check.
I looked at the Diode assembly but not really sure how it shold be connected. Maybe will go with the "fridge switch" as that seems more understandable.
Regards
T1 Terry