Parallel buck converters diode questions

[GlennWest]

Need to add additional dc power and considering adding a second dc/dc converter. From research I have learned a diode/rectifier will allow me to do this. The purpose of the diode is to  allow the units to isolate each unit from the other. I have a fairly large amp unit now, 60 amp, and really could get by with a 30 amp added if it will work.  Seeing the diode isolates each converter will the different amps matter. Also I see rectifiers with 4 wires. None with just two wires.  Also would a battery isolator do the same thing.  Here is a diode that looks like it would work. https://www.amazon.com/Rectifier-70HFR120-Polarity-Batteries-Converter/dp/B083V1QP4L/ref=sr_1_12_sspa?keywords=high+amp+dc+diode%2Frectifiers&qid=1638378263&sr=8-12-spons&psc=1&smid=A3VAOAURHASR38&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUE5VklITkc4TThWR0QmZW5jcnlwdGVkSWQ9QTAyMjg5NzMzT0JJVVE3UFpYODFDJmVuY3J5cHRlZEFkSWQ9QTA5MTMwMzIyRlIySEdWWjZMNTQ0JndpZGdldE5hbWU9c3BfbXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Edited December 1, 2021 by GlennWest

[palmeris]

My experience with diodes and bridge rectifiers with low voltage systems is a diode will allow dc voltage to pass in one direction.  A rectifier is 4 diodes arranged in a circuit that 2 ac input leads connect to and other 2 leads will output dc...so 12volt ac to 12 volt dc for example.  The diodes are sized by wattage that will pass thru them. Not sure if that helps you with your questions. 

[Jaydrvr]

A battery isolator will do the same thing, since it's actually just two diodes connected together at the output. A rectifier has four diodes connected in a way to "rectify", or convert alternating current to direct current. That's not what you need for your application, although in theory you could use half of the bridge to do what you need. Jay

P.S. Actually, in thinking it over, the battery isolator won't work, because the electrical flow goes the wrong way. You need the flow to the combined end, not from. Hope that helps.

Edited December 2, 2021 by Jaydrvr
Correction

[GlennWest]

Yes, Battery isolators looked good until I discovered the direction. Think I will give the diode a try. Some have tried to parallel my unit but didn't isolate them. Didn't work just paralleled. Those I linked are the most promising ones I have found. 

[oldjohnt]

10 hours ago, GlennWest said:

Also I see rectifiers with 4 wires. None with just two wires. 

Glenn, that (4 wires) sounds like a Wheatstone Bridge RECTIFIER (uses 4 diodes) with 2 AC terminals IN and 2 DC + and - terminals OUT. Rectifiers can be Full Wave or Half Wave. A single Diode alone still acts as a Diode IE passes current in one direction but not the other. What you linked are simple Diodes which can be used as battery isolators and as rectifiers, but you're talking DC and DC for blockage and isolation NOT AC to DC Rectifiers. Your batteries etc are DC no need to rectify AC to DC, you already have that.

 So long as they are rated to handle the current and voltage sure those Diodes will allow current flow in one direction but not the other. They typically can have a 0.6 Voltage Drop across them. 

 John T

 

[GlennWest]

They are 70 amp and my unit is a 60 amp. Will add another 60 amp dc/dc unit. I can get 80 0r 100 amp diodes like I linked. Would I need more than the 70 amp diode? That link is a pack of 10, 5 reverse and 5 forward.

Edited December 2, 2021 by GlennWest

[Mark and Dale Bruss]

Battery combiners are relays that are set you open when the direction of current is not what you want.  They can be set to transfer current either way.

There are many battery combiners like Amazon.com: Victron Intelligent Li-ion Battery Combiner Cyrix-Li-ct 12/24V - 120 Amp : Sports & Outdoors

The advantage of battery combinators over diode isolation is that diode isolation always drops .6 volts across the diodes.  When the contacts of the battery combinators are closed. there are 0 volts lost.

Discussed in Battery Combiner (dmbruss.com)

[Jaydrvr]

59 minutes ago, Mark and Dale Bruss said:

Battery combiners are relays that are set you open when the direction of current is not what you want.  They can be set to transfer current either way.

There are many battery combiners like Amazon.com: Victron Intelligent Li-ion Battery Combiner Cyrix-Li-ct 12/24V - 120 Amp : Sports & Outdoors

The advantage of battery combinators over diode isolation is that diode isolation always drops .6 volts across the diodes.  When the contacts of the battery combinators are closed. there are 0 volts lost.

Discussed in Battery Combiner (dmbruss.com)

All true of course, but I think Glenn's primary concern - and mine as well - is about backfeeding from one converter into another. Is that not something that needs to be worried about? A combiner is not going to prevent backfeeding. Jay

[Mark and Dale Bruss]

Actually, a battery combiner will prevent back feed.  The normal setup is that when the voltage of the feed side drops below the voltage of the other side, the contacts open preventing back feed.  This system worked well on my boat where I did not want the starting batteries to draw down the batteries running the bilge pumps.

[Jaydrvr]

10 minutes ago, Mark and Dale Bruss said:

Actually, a battery combiner will prevent back feed.  The normal setup is that when the voltage of the feed side drops below the voltage of the other side, the contacts open preventing back feed.  This system worked well on my boat where I did not want the starting batteries to draw down the batteries running the bilge pumps.

Yes of course, that makes sense. My memory isn't what it used to be, but then...what is?? Jay

[GlennWest]

16 hours ago, oldjohnt said:

Glenn, that (4 wires) sounds like a Wheatstone Bridge RECTIFIER (uses 4 diodes) with 2 AC terminals IN and 2 DC + and - terminals OUT. Rectifiers can be Full Wave or Half Wave. A single Diode alone still acts as a Diode IE passes current in one direction but not the other. What you linked are simple Diodes which can be used as battery isolators and as rectifiers, but you're talking DC and DC for blockage and isolation NOT AC to DC Rectifiers. Your batteries etc are DC no need to rectify AC to DC, you already have that.

 So long as they are rated to handle the current and voltage sure those Diodes will allow current flow in one direction but not the other. They typically can have a 0.6 Voltage Drop across them. 

 John T

 

A .6 voltage drop might cause problem. I am at 12.27 v. 

Edited December 2, 2021 by GlennWest

[GlennWest]

4 hours ago, Mark and Dale Bruss said:

Battery combiners are relays that are set you open when the direction of current is not what you want.  They can be set to transfer current either way.

There are many battery combiners like Amazon.com: Victron Intelligent Li-ion Battery Combiner Cyrix-Li-ct 12/24V - 120 Amp : Sports & Outdoors

The advantage of battery combinators over diode isolation is that diode isolation always drops .6 volts across the diodes.  When the contacts of the battery combinators are closed. there are 0 volts lost.

Discussed in Battery Combiner (dmbruss.com)

Please explain how I could use that with my buck converters. All I saw had 1 supply (alternator) and two batteries. I need opposite.

[Mark and Dale Bruss]

2 hours ago, GlennWest said:

A .6 voltage drop would make it unusable. That would be less than 8 volts left

That is 0.6 volts meaning 13.4 volts from 14.0 volts.  Worse is only 12.6 volts from 13.2 volts.

[GlennWest]

Done math wrong. At 12.27 so less than 12 left.

[GlennWest]

I may be good with current unit once I fix the hydraulic system. I can close valves and operate each slide independently. Way less amps used that way. And lights only dim on last slide when at end of stroke when it bypasses or whatever causes this. But it interesting topic regardless. 

[Jaydrvr]

Sounds like you have it all worked out. That's a good thing. Seems to me that you could use a latching relay on each converter leg to safely connect and disconnect independently as needed, as another possible solution. Jay

[GlennWest]

Found some battery combiners with 2 inputs. Reasonable price. If need to go that route. Diode too much loss for my buck converter. Even the Schottky diode would be too much. At 12.27 not any room for loss.