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leftbrainstuff · 20-11-2018, 11:12

This seems way too complicated. Here's my $0.02.

Connecting house bank to dink batt is very wasteful and you have no house protection if the dink batt suffers a short or similar fate including gradual loss of batt capacity over time. This will invariably pull both batts down.

Using junk connectors like cigarette lighter sockets is asking for trouble. They'll also probably act as another unnecessary voltage drop.

You want some form of transformer between both batteries. Why not use an AC to DC inverter or even a DC to DC converter. Size it appropriately, connect it properly and just pick one from Amazon that has reasonable reviews. The key is to pick something that will disconnect your dink batt once its charged.

Or remove the batt from the dink each night and put on the boat in a proper receptacle with an echo charge (just a DC to DC converter or current limiter) or similar

sparrowhawk1 · 20-11-2018, 11:18

Now we're getting somewhere. So constant-current doesn't mean it will limit the current from my house to my trolling? Once again I'm not looking to top my battery I just want to put two to three amps constant into it overnight. And I keep saying I just want because you keep saying it won't do things that I'm not even talking about.[emoji48]
One time I put a link out and it gave a bunch of my personal information so that's why I started taking photos.

sparrowhawk1 · 20-11-2018, 12:22

If a moderator could check out this link and make sure my personal information isn't being shared I would appreciate it.https://youtu.be/oxy10TYGh5A

this is a link to using a dc-dc boost converter to charge a laptop with a 12-volt battery.

sparrowhawk1 · 20-11-2018, 13:34

I'm surprised a a guru hasn't advised me that a combo buck, step-up converter is much less efficient than just a step up converter.[emoji37]

LoudMusic · 20-11-2018, 13:53

I've skimmed this thread as I have interest in an electric outboard for my dink(s). I also want to do it "right". That leads me to believe charging the dink batteries from the yacht's solar panels directly is the most logical path.

I've had a quick look at the Victron MPPT chargers. I have a single SmartSolar 100/50 on board currently with prospect of adding two more and additional panels. But this model doesn't have "load" lugs. Turns out only smaller models have a secondary output.

Does anyone know why their product line only has secondary outputs on smaller controllers?

john61ct · 21-11-2018, 08:28

OP your personal info is not transmitted by YT links. For Amazon eBay etc just trim the URL only leaving the item#.

Quote:

Originally Posted by leftbrainstuff

Connecting house bank to dink batt is very wasteful and you have no house protection if the dink batt suffers a short or similar fate including gradual loss of batt capacity over time. This will invariably pull both batts down.

Already covered, a dozen times. OP states he doesn't care.

> Using junk connectors like cigarette lighter sockets is asking for trouble. They'll also probably act as another unnecessary voltage drop.

Yes, OP understands that much by now.

> You want some form of transformer between both batteries. Why not use an AC to DC inverter or even a DC to DC converter.

That last is exactly where we are. Guess you didn't read the thread? Recommend one.

> The key is to pick something that will disconnect your dink batt once its charged.

That would be a DC-DC **charger**, and drop to Float, not disconnect. I'd love to find a simple device that disconnected, please link to one.

OP wants to spend $20, states does not want a charger.

> Or remove the batt from the dink each night and put on the boat in a proper receptacle with an echo charge (just a DC to DC converter or current limiter) or similar

Yes that option was discussed already.

john61ct · 21-11-2018, 08:36

Do you think being unpleasant encourages people to help you? It doesn't. We are all volunteers here, an attitude that you are entitled to have your problem solved by an expert post-haste is puzzling to me. I've already suggested other forums where you are more likely to get better advice, but I suggest you ask nicely, with more humility.

Quote:

Originally Posted by sparrowhawk1

So constant-current doesn't mean it will limit the current from my house to my trolling?

We need a context, link to address that. Limiting the current draw is likely not relevant except as something you want, if it is too high.

Again, the amps flow is determined by the wire, batteries size and resistance, and is something you need to measure for your setup as I outlined, in order to ensure you don't fry the DCDC converter.

Or as discussed you just size its ampacity much higher than you imagine the flow to be.

john61ct · 21-11-2018, 08:39

Quote:

Originally Posted by sparrowhawk1

I'm surprised a a guru hasn't advised me that a combo buck, step-up converter is much less efficient than just a step up converter.[emoji37]

You never mentioned a need for a buck / boost unit, nor any concern about efficiency.

This whole idea is the opposite of efficient, that was made clear dozens of times.

You stated you only need a boost DCDC converter, and you want cheapest. Why would you waste money on the buck functionality?

john61ct · 21-11-2018, 08:40

Quote:

Originally Posted by LoudMusic

I've skimmed this thread as I have interest in an electric outboard for my dink(s). I also want to do it "right". That leads me to believe charging the dink batteries from the yacht's solar panels directly is the most logical path.

I've had a quick look at the Victron MPPT chargers. I have a single SmartSolar 100/50 on board currently with prospect of adding two more and additional panels. But this model doesn't have "load" lugs. Turns out only smaller models have a secondary output.

Does anyone know why their product line only has secondary outputs on smaller controllers?

Please start a new thread, this one is already pear-shaped dealing with one set of issues.

**noelex 77** · 21-11-2018, 09:22

Here is a relatively inexpensive (about $150 in Europe, but probably cheaper the USA) marine dc to dc battery charger.

This is a safer solution than you are proposing, does not require any electrical knowledge, and your battery will be happier.

john61ct · 21-11-2018, 09:28

Yes OP, we realize you "want" a $20 solution, these suggestions are more for others coming along, don't have a cow.

CTEK 250S Duo is pretty bulletproof, limited to 20A. Have got a few off eBay in the $80 - 120 range over the years, pretty bulletproof and include a rudimentary solar controller for free.

But not voltage adjustable like the Sterling BBs.

sparrowhawk1 · 21-11-2018, 10:57

Texting back and forth can be weird, I did not mean to be rude asking if constant-current meant it would limit the current.( It was after saying I only want to draw 3 amps max with a 8 Amp 12 Amp Max converter and being told it was too small) I am interested in efficiency I think I made that clear. But I don't want to have a high cost product in my dinghy. round and round[emoji15]. So sit back if you can't recommend a dc-to-dc converter I'm going to buy one soon and will give the results.