Thread: DC/DC chargers, How do they work and do you really need one.

Originally Posted by Barraman

I’m very conscious of hyjacking this thread. I made a simple observation that was relevant - I have replaced the VSR’s in both my boats with DC-DC chargers, and find them to be more effective. How do I judge that? Simply because the ‘low voltage’ warning doesn’t come onto my Humminbird Helix 12 mega sounders as often as used to be the case. Another motivation was that I know of two VSRs that have shorted out and burnt. All the commentary does not change my observation.

Originally Posted by drivesafe

Barraman, your comments are not hijacking this thread, they are exactly what was ask for by the OP.

Could you post up more detailed info about your system?

I'm going to take an educated guess. about what Barramans system (or the ones hes known io)

DC/DC chargers are typically a "soft start" system with no mechanical contacts opening and closing to short out.

VSRs (in fact any relay) can suffer from numerous methods of failure one of which is arching of the primary contacts that create a high resistance due to carbonising of the contact points. (also corrosion in a wet environment) if this results in say half a volts worth of drop then battery recharge rates are effected exponentially(ish).

The arch is exaggerated if the relays are expected to carry loads over their peak/surge/constant current design limits.

My guess..

a dual battery system with an alternator charging one battery and the VSR then connecting the second battery (with the load attached) when the voltage of the first battery/charge system is at a voltage high enough to indicate that the first battery is sufficiently charged AND the primary charging system is charging (usually around or higher than 13.8v) This leads to the relay taking not only the charge current from the alternator but also whatever the cranking battery can throw into the mix as well.

an also ran...

if the primary contacts are operating at a lower voltage (or it might be a DC thing) than designed you can wind up with a bizzare kind of electro plating occuring which then become an insulator. I'm not even going to pretend i know how or why but it seems to be prelevent in humid areas. I've seen it a few times when guys have used 250vac relays as isolators on small solar pump controllers. Switch the relays out for lower rated relays and no more issues. If the VSR's are driving relays that are AC voltage rated this might have been the cause.

Originally Posted by drivesafe

Barraman, your comments are not hijacking this thread, they are exactly what was ask for by the OP.
Could you post up more detailed info about your system?

Oh dear - you asked for it, so here goes!

There are 4 stages to my battery/VSR/charger experience with the larger of my two boats. The boat is a 6.7 M glass/composite custom build, side console 'barra boat' ,with front and rear casting decks. O/board is a Yamaha 250 Vmax SHO on a Bob's Machine Shop jack plate. Up front is a Minn Kota Ulterra 112lb 36V trolling motor. It has 4 x combo sounders (Humminbird Helix 7 in the console, Helix 10 and Helix 12 G2 mega SIs above the console, and a Helix 12 G1 SI on the front deck - I think they can each draw 1.75A). I run 4 x transducers, including a Humminbird 360.

We only use the outboard to get to where we want to fish (often a 20 - 30 nm run) and to change spots, and then spend most of our time on the electric trolling motor. We are mono-species fishermen - lure chuckers for barramundi!

Stage 1: 1 x 120 Ah AGM 'start' battery and 1 x 120 Ah AGM 'house' battery connected via a standard BEP unit that included separate master switches for the start and house batteries, a switch that connects the two batteries in parallel for and "emergency" start, with the VSR between the start and house batteries. The trolling motor is on 3 x 120 Ah AGM batteries that are quite separate from the start and house batteries in any way. The two sets of batteries were put on separate mains smart chargers overnight on multi-day fishing trips.
After long periods just on the batteries without running on the outboard, I would get 'low voltage' alterts on the sounders.

Stage 2: I added a second 120 Ah AGM battery to the 'house' (connected in parallel). Better - but still ran out of grunt, as our time on the water also was increasing - 12 hr days of which only maybe 2 were with the outboard running but the electronics were all on.

Stage 3: Someone suggested ditching the VSR for a 12v DC-12v DC charger, so I fitted a Sterling Pro Charge B 20A unit. Problem with the sounders was solved but now I had a new problem. We were now spending a week at a time fishing the McArthur R in the NT and after about 4 days the trolling motor batteries were starting to struggle. They were not getting sufficient charge overnight and were slowly running down.

Stage 4: I fitted a Sterling Pro Charger B 12v DC - 36v DC 30A unit between the two 'house' batteries and the three trolling motor batteries.

PROBLEMS SOLVED!

We can fish all day for days at a time without running out of power. My mates suggested that I install a small thermonuclear power plant - but that doesn't seem to be required at our present level of activity.

When mains power is available the start/house batteries are on a Sterling 240v - 12v DC smart charger, and the trolling motor batteries are on a Pro Mariner Pro Sport 20 Plus 20A triple bank (3 x 12v DC) charger. I have a master switch installed to disconnect the 12-36v charger when the trolling motor batteries are on the mains power charger.

Yes, the boat has 6 x 120 Ah AGM batteries - and they are HEAVY! I would like to change to lithium, but I don't quite trust them. Fires on boats scare the crap out of me - patricularly when fishing in croc and shark central!

Have you considered adding a solar panel to keep the trolling batteries charged while out remote?

Gees,, am I the only one here that just wants a pic of his bloody boat!!!

sorry Trout...

Originally Posted by Pedro_The_Swift

Gees,, am I the only one here that just wants a pic of his bloody boat!!!

sorry Trout...

Forget the pic, how about an invite

Deano

Originally Posted by DiscoMick

Have you considered adding a solar panel to keep the trolling batteries charged while out remote?

Yes I have but there is nowhere to put one ATM. There may be a small hard-top in its future.

Originally Posted by Barraman

Yes I have but there is nowhere to put one ATM. There may be a small hard-top in its future.

put em on a small float with a drag cable and wiring.

Originally Posted by Pedro_The_Swift

Gees,, am I the only one here that just wants a pic of his bloody boat!!!

sorry Trout...

All is good Mate, I wouldn't mind have a squiz at it myself it sounds like a good rig for barra bashing