DC to DC battery chargers

**clubagreenie** · 15th March 2013, 07:11 PM

I don't have anything again solenoids.

In fact my preferences run even simpler, a pair of big **** off hella truck isolation switches (the ones with the metal key not the cheesy red plastic ones).

I have large issues with ****heads, very large issues.

**Blknight.aus** · 15th March 2013, 07:19 PM

nor do I infact I have several not ****ing about ones waiting for fozzy, unfortunately I had to make the dual battery system SWMBO safe while retaining my requirements so 200A solenoids it was.

additionally, and I may be quoted on this....

IF you buy a traxride unit, aren't reasonably capable of DIY, can get all the gear to me, aren't on my **** list/owe me money list, buy any/all the extra cabling and crimps, take responsability for prepping for cable routing and panel work required, and provide or compensate for workshop consumables for the job.

I'll do the fit work for you FREE, The units are THAT good. I would rather spend time sending you off with something that I KNOW works that's installed properly than risk something going badly wrong somewhere down the track.

**Mick_Marsh** · 16th March 2013, 06:42 PM

Originally Posted by drivesafe

Hi Mick_Marsh and why do you think you need a DC/DC device to be able to run your fridge of a battery?

This is where you educate me.
I thought a solar panel has a variable voltage and current. I've seen car alternators with stuffed regulators cook batteries. Is a solar panel regulated or unregulated? Is it possible to cook a car battery with a solar panel?

**Mick_Marsh** · 16th March 2013, 06:50 PM

Originally Posted by Blknight.aus

my money says because the salesman told him he needed one in place of a mmpt solar regulator because the markup on a $200 DC-Dc charger is better than the $50 mmpt regulator.

Salespeople don't know their products any more. They just sell wigets. Some wigets come in a cardboard box and some wigets are smaller and hang on a hook.
I have been browsing the Jaycar catalogue. I may have thought a mmpt regulator was a dc/dc charger. Do they not both use dc as an input, output dc and trickle charge a battery?
That is what I want to do.

**Mick_Marsh** · 16th March 2013, 06:58 PM

Originally Posted by scanfor

On a more constructive note, I agree with others that you only need a MPPT solar controller, a VSR (Voltage sensitive relay) to isolate the system from your crank battery, and the proper size cable to minimise Voltage drop to the deep-cycle battery.
That's the arrangement I've used for the past 5 years and the fridge runs all day every day without problems.

The fridge battery will be isolated from the crank battery quite well.
I'm using a very good dielectric (provided it doesn't get ionised) and lots of it. A few metres of air.
Yes, the system is not attached to the car.
Voltage drop should not be a problem as it is being trickle charged. Very low current.

**Blknight.aus** · 16th March 2013, 07:57 PM

Originally Posted by Mick_Marsh

Salespeople don't know their products any more. They just sell wigets. Some wigets come in a cardboard box and some wigets are smaller and hang on a hook.
I have been browsing the Jaycar catalogue. I may have thought a mmpt regulator was a dc/dc charger. Do they not both use dc as an input, output dc and trickle charge a battery?
That is what I want to do.

ermm, no. In simplistic Real world terms....

A dc-dc charger typically takes a constant DC input and turns it into a different constant output intended to charge the battery. It doesnt care whats coming in on the input side because its assumed that its only going to be hooked up when the providing battery is either already on a charger or is being charged by the alternator.

The concept is that if you have a 2v drop in the line between the supplying battery and the input of the dc-dc charger what it will do is draw more amps do some switchmodery and filtering then pump out the correct charging voltage but at lower amps. on a long enough time line this will get your battery to a higher state of charge than just relying on the alternator and your 2v line drop.

an Mppt solar regulator does the same thing BUT its got a few other tricks up its sleeve. First of is it offers shaped charging you need to select a single state one that is appropriate for your battery (flooded, SLA, Gel, AGM, and now litium and nimh are making appearances too) or program it.

The MPPT puts a constant load on the panels (which helps reduce thermal shocking on the panel when loads cycle on and off) and provides the correct charging rate to the battery... Big whoops... whats really clever is that good units will monitor whats going on, if the batteries are fully charged and the sun is shining then the charger will offer nothing to the batteries and use the suns juice to run the load But on top of that it will also ensure that the voltage at the output is always at the nominated out put voltage even if the optimal charging voltage for the batteries is higher. It will also cut isolate every thing from everything to protect battery against battery, panel and load damage from voltages over or under nominals.

if you wanted to be simplistic about it about it a decent MPPT solar regulator is built up of a

DC-DC charger that always correctly charges the battery
DC-DC Regulator that always ensures the load has an appropriate maximum voltage
A battery protection circuit
A Dummy load For the panels

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