Printable View
This thread has come about because the OP wants to know DC/DC charging and we had a quick discussion via PMs, after another thread was removed.Quote:
Originally Posted by V8Ian
I would like to hear more of what people expect if they use DC/DC devices and I will post up data based on testing I have carried out over the last decade or so and then readers can make up the own minds, based on FACTS.
Here’s another known companies take on it:
http://www.home12volt.com.au/uploads...e_charging.pdf
And another:
DC to DC Converters Explained - Enerdrive
In its simplest terms - a step up transformer - usually with some smarts added.
One thing often touted is that you can run thin cable with a DcDc unit. This is not correct if you want it to work correctly/efficiently.
Any transformer (and we will assume 100% efficiency to make it simple) does a simple equation:
If you double voltage, you halve current. So, if you had 6v coming in and wanted 12v coming out you need a 1:2 transformer.
Now let’s say you choose to have 25a on the 12v side. You’ll need that 6v input side to have 50a coming in.
In a vehicle running at say 12.4v and you want 13.8v the equation closes the gap considerably.
V=I*R and P=I*V come into play. (Those laws)
13.8v and 25a = 12.4v and around 27.5a (if my heads playing nicely, it’s been a long day)
Drop that down to 11v (allowing for voltage drop in long thin cable for example) and you’ll need to try and pull 25% more current to make the output - that’s now 32a to make the same 13.8v/25a output.
As you can see, the constraint is the output side - where the units maximum is 25a in this case.
Remember Amps(ah) are what we need to replace and volts are what is used to push this into a battery (volts is flow) volts.
I should have said MOST vehicles post 2006 have a variable voltage alternator, My Bad.Quote:
Originally Posted by scarry
But If you want to run an auxiliary battery Maybe you should do some research to find out what alternator you are running[thumbsupbig]
2006 is a "Ballpark" era because this is when the alternators were altered because of emissions OK
From a 4x4 perspective, 2005 D3 was the first SMART variable voltage RV.Quote:
Originally Posted by trout1105
2008, Toyota introduced their LOWER operating voltage, time/temperature compensated alternator operation.
around 2011 Nissan and others started different versions of variable voltage operations.
Today, most 4x4s have some version of either SMART or not so smart variable voltage alternators.
Whether you need a DC/DC device or not, is still a user decision, but the user needs correct info in the first place.
I will try to show how DC/DC devices actually work and end users can make up their own minds about what will suit their specific needs.
Back to the request for people to post up how they thing DC/DC device work.
NOTE this is not a trick question, I would just like to hear what peoples opinions are about how they think DC/DC devices work?
I have NO idea HOW these devices work But I have a pretty good idea of what they are capable of, Much like when I use my smart phone as I know what I can do on it but I am Clueless of how it does what it does.Quote:
Back to the request for people to post up how they think a DC/DC device works.
I would Love to know how the DC/DC devices do what they do[thumbsupbig]
My suspicions are that you probably do, just don't yet realise it.Quote:
Originally Posted by trout1105
My thoughts are that they're operation is 'just like' a 240v modern smart/multi stage battery charger, with the main difference is that instead of 240v coming in(then rectified and transformed) the input is 12-14 or so volts coming off the vehicle electrical system.
Like Tombie said, you're vehicles volts in plus whatever amps can be allowed through the input side(ie. Watts) will give you a digitally regulated output for the battery type you want to charge up.
Think of them in this manner: take a typical modern battery charger like a C-tek type. Also take a 12 -> 240v Inverter with you on your travels. Hook up your inverter to the car, hook up the Ctek to the aux batteries .. basically the same thing only a bit less wasteful.
If you're auxiliary batteries are flooded cells, sounds to me like a bit of waste of $s.
If any other type like AGM or Lead Crystal or whatever is 'the next best thing since sliced bread' ... then they can be handy to keep the auxiliary batteries in better shape.
More importantly the question(ie. if you need them) would be better answered if you stated the type of batteries you have as the auxiliaries in whichever vehicle you want to use it for.
The way I'm seeing it is that, say for example you want the Redarc 40 Amp model to charge your 200Ah aux regular flooded cell batteries.
Your alternator can output near on 100A. So you can run the DC-DC no worries, as the input side(your car) allows about 1200W or so of power into the DC-DC.
But now, you have 40 amps output for those 200Ah aux batteries, as that is as far as the DC-DC will allow.
But, if your aux batteries were AGM which usually require 14.7v, just using a normal VSR solenoid won't give you that in most vehicles(if any. Your D2 won't!!), so the AGM could be an advantage, even tho it's still only allowing 40Amps through to the batteries.
The advantage being the 14.7 volts when set to charge AGM batteries.
If you have a smart battery charger at home(the multi stage/Ctek type that allows you specify a battery type) .. think of it as the same thing, difference being that it's not 240v mains input, it's typical vehicle input .. some usually say 9-30v, so can work in trucks and stuff too.
But in your hypothetical application(say the D2) the input is going to be about 14v .. 13.8 to about 14.4 from what I've seen out of my Discos so far.
I'm not exactly sure your setup(s) but sounds like one main battery for starting and then two auxiliary batteries down back for power usage. You have a solar panel too.?
If this is right, I'd leave the anderson plug in all the time so that the batteries just charge up .. assuming a regulated solar panel for the aux batteries.
Leave the anderson plug in, assuming that the solar is charging up the system.
The standard 'dumb' VSR will keep the starter battery connected for a period after shutdown, and with the solar charging the system now, it will keep the VSR on and continue to keep the starter battery topped up too.
If you don't have a regulator on the solar to the aux batteries, don't do the above.
I've done this many times, not with solar, but the 240v charger, where I've connected it to the aux battery after getting home. It keeps the starter battery topped up for example if it's going to be a bit frosty the next morning.
Oh! and the reason I pop it on the Aux, is sometimes I park in a certain spot and the cable lengths are just perfect. But the point is that some VSRs have reverse sensing ability(Redarc does), so any charging power coming into the aux will also charge the starter.
A topped up start battery is better than one sitting un topped up, yeah?
The other thing that is a bit unclear is your solar setup. Sounds like it's hard mounted to the roof or something. So always connected and hence charging the aux batteries all the time?
So, you have a VSR fitted and solar always on fitted? If you have a VSR, which one?
I drive my D2a on a regular basis and the shortest run is about 30K round trip so I don't need to keep the cranking battery "Topped Up" via a 240v charger or a solar panel.
My VSR is a Redarc unit But with a 160w solar panel running through an MPPT controller to 2x 110AH AGM batteries and only running a 40l Engle I have little need of it now in WA with all the sunshine we get.
I fitted the VSR prior to fitting the solar setup so now it is pretty much redundant except for prolonged days of cloud cover.
IF I didn't have the solar system fitted I would most likely fit a DC/DC device to run my "House" batteries on the D2a[thumbsupbig]
zQuote:
Originally Posted by AK83
This is not correct. 14.7v is the MAXIMUM SAFE CHARGING VOLTAGE for most AGMs.
AGMs can actually be FULLY CHARGED with much lower voltages.
The exact MINIMUM required charge voltage is only available from the battery manufacturer’s specs.
For example, an Optima can be charged safely charged with up to 15v, but can be fully charged with as little as 13.65v.
Knowing the maximum voltage simply means you can choose the voltage that will charge the battery in the shortest time.
Quote:
Originally Posted by trout1105
If you fitted a 50 amp DC/DC device and your two 110Ah batteries were down to 20% SoC, you will need at least 6 hours of driving to get them back around 100%.
Here is the charge profile of a 25 amp DC/DC charge ( 20 amp maximum output current )
WILDESIDE - OPTIMA D34 TEST CHARGE - 06/07/19.
Optima D34 55Ah Yellowtop charged from 30% SoC after being discharged down to 11.71v using a 2 amp load, drawing a total of 35.7Ah from a fully charged state, reached at 08:27, Voltage settled up to 12.67v at the start of charging cycle with a Sterling Wildside - 25 amp Battery to Battery Charger -.
The Wildside was powered via a bench power supply, so that there was a constant 14.5v to see how quick the Wildside could recharge a battery in perfect conditions.
The first column is the TIME, the second column is the TERMINAL VOLTAGE at the battery, the third column is CHARGING CURRENT, the forth column is the amount of used battery capacity replaced at each time reference and the last column is the percentage of replaced used battery capacity.
11:02 11:83v 00.00a 0a
11:04 12.67v 19.35a 0a
11:34 13.06v 19.16a 9.591a 25.5%
12:04 13.55v 19.07a 19.160a 51.0%
12:34 14.94v 14.88a 28.285a 75.2%
13:04 15.00v 06.02a 33.270a 88.5%
13:34 15.04v 02.37a 35.216a 93.7%
14:04 15.09v 01.09a 36.027a 95.8%
15:04 15.12v 00.46a 36.723a 98.0%
16:04 15.14v 00.28a 37.083a 98.6%
17:04 15.15v 00.22a 37.326a 99.3%
18:04 15.15v 00.17a 37.518a 99.7%
18:25 15.15v 00.16a 37.579a 100%
The Wildside went into FLOAT at 18:26
Attachment 161109
Ah! AGM as the aux.Quote:
Originally Posted by trout1105
Then obviously the MPPT controller would be set to AGM mode, so you wouldn't keep the anderson plug connected as the solar controller will over charge the stater battery. (I think).
If your start battery is also AGM, then I'd keep the anderson plug connected so that the start battery also gets a top up.
What gauge cable do you have from start battery to isolator(Redarc) to aux batteries to MPPT controller?
One could assume that with the 160w panel, you're probably getting something like 10 amps(+-2A) through it.
If the start battery is not AGM, dunno if it'd be wise to keep the anderson plug connected all the time. I guess that'd depend on the voltage drop from the aux though the Redarc onto the start batt.
I doubt it'd be too much tho, so most likely you would disconnect it if it's a std SLA battery.
But all that is dependent on whether the Redarc is the 'D' model. Not exactly sure if the non D model would do the same thing, but as long as the car has only recently been shut down, battery voltage should be high enough to keep the VSR activated, which will keep the start battery topped up anyhow, to keep the VSR activated .. ad infinitum ...
Just as an example, our Defender's flow, measured at the dash, just sits constantly on 14 volts.
The Anderson plug on the rear bumper outputs a steady 8 amps. That seems perfectly adequate to keep the camper's 2 x 120Ah AGMs charged.
