DC to DC charger - not needed for boats with proper alternators.

[Putt-Putt]

Originally Posted by newhaul

No the renogy dc to dc connects direct from alt to dc dc to lifepo4 the u1 is kept in its position and connections to the alternator . Just like any start battery

OK got it, you are going to connect the DC-DC's input terminals directly to the alternator, without them never landing on a battery.

That is different than shown in the DC-DC's manual.

[newhaul]

Originally Posted by Putt-Putt

OK got it, you are going to connect the DC-DC's input terminals directly to the alternator, without them never landing on a battery.

That is different than shown in the DC-DC's manual.

Technical here I know but the alternator charge wire runs from alternator to starter main battery positive connection. The input of the renogy dc dc charger will be connected there . Or it can be at the positive terminal of the battery the negative will connect with the main system ground on the engine block.

No the connections don't ever have to be directly on the start battery just in the circuit.

[Putt-Putt]

Well, thats different now. The DC-DC's positive input terminal is now connected to a battery, otherwise the engine could not start.

In my mind stacking the lugs of high current circuits on to the starter lug is never a good idea. How many are on there now 3, 4, more?

If it was me I would move the alternator and the DC-DC to the batteries or better yet, a positive busbar.

Regardless, have a good time installing your 4th backup charge source in this often grey and windless environment.

[wholybee]

Originally Posted by Putt-Putt

OK got it, you are going to connect the DC-DC's input terminals directly to the alternator, without them never landing on a battery.

That is different than shown in the DC-DC's manual.

It doesn't matter. It could go from the Alternator to the DCDC to the battery, or the alternator to the battery to the DCDC, or the alternator to a buss bar to both. Electrically those are all the same circuit and do exactly the same thing.

[newhaul]

Originally Posted by Putt-Putt

In my mind stacking the lugs of high current circuits on to the starter lug is never a good idea. How many are on there now 3, 4, more?
.

Sorry but what's the problem with placing a 6 agw. Lead on a lug that already has a 2/0 Lead for feeding the starter. That means a 2/0, a 6agw and a 10agw on a 1/2 in copper stud what is your issue there?

[CaptainRivet]

Originally Posted by newhaul

Where are you getting the 1500 rpm from my westerbeke is 2200rpm engine with a 2.5 to 1 pully set from crank to alternator which is speed to optimum of 6k rpm
Somreal close not worried about heat .

How is my system heavily modified?

please explain to an engineer how his engineering is wrong.

Mixed yours up with someone else who has a also a 75A or 90A but remanufactered, upgraded 120A diodes and rectifier.
A stock 75A you normally can be happy if it withstands 40A continues longtherm. So that yours can do its rated 75A continues is impressive.
I just took 1500rpm as typical rpms for motorsailing, which means its not reving fast and relying mostly on its self cooling capacity plus runs long hours. Thats a typical spot when most fry their alternators as a typical 100A one can do 30-40A then but eg a 60A DC2DC or A big AGM or LFP demand full output.

In your setup you could simply use an Victron argofet splitting diode and connect LFP and starter parallel. Then alternator charges always with max it can do/what SoC requests. The lead is surge, spike protector and always a high resistance load incase BMS switches LFP off. You don't need the different stages of a DC2DC if its your 4th backup like i have it too. It does bulk, your solar and/or wind absorption. Simple, cheap and reliable setup as you cannot mix/forget switches.
Or simply add a 2nd LFP instead starter, parallel them to a hybrid starter/house bank even if they different capacities no problem and put LVC at 3.0V so the LFP has always enough juice to start engine. Perfect for that are 40 till 60AH winston cells, you sometimes get this smalls ones for a good discount as not in high demand and the new series are rated 5C which is basically a LTO with the energy density of a LFP and its better voltage range for 12V.

[Fuss]

Perhaps a little less quantity and more quality CaptainRivet. You reply to too many posts when you are not really qualified to do so, this is constantly creating confusion and uncertainty, especially for forum users who look to these forums for advice. Clear non confusing explanations from users with actual personal experience is what is needed, not regurgitated unclear content from previously read websites.

[CaptainRivet]

Originally Posted by Fuss

Perhaps a little less quantity and more quality CaptainRivet. You reply to too many posts when you are not really qualified to do so, this is constantly creating confusion and uncertainty, especially for forum users who look to these forums for advice. Clear non confusing explanations from users with actual personal experience is what is needed, not regurgitated unclear content from previously read websites.

Who are you to judge this???
Who is constantly making wrong statements about a eve 280AH starting 1400CCA starter and dozen other stuff.

I am working with LTO and lithium batteries incl alternators since 25 years where noone even heard of them, first set of llithium scraped of a military vehicle in 1997...doing competion car audio ( been european champ several times) and racing (hill, curcuit,slalom, ralley) since 30 years....burned a car down, tortured dozen lithium (and more lead) to death, melted cables and learned my lessons from testing limits and beyond, not from the armchair. Additional a very good friend runs an NPO making LTO/LFP storage walls and developing EVs. He gets eg every 14 days a container from EVE factory and was the first who imported Yinglong LTO cells into europe. Thats where i get my cells from and lab testing results...
And still learning..and making mistakes.
What do you have to offer to qualify to make such a statement?

[Putt-Putt]

Originally Posted by newhaul

Sorry but what's the problem with placing a 6 agw. Lead on a lug that already has a 2/0 Lead for feeding the starter. That means a 2/0, a 6agw and a 10agw on a 1/2 in copper stud what is your issue there?

The issue here is that the readily available battery lugs are not designed to be stacked. There are purposely designed stacking power lugs that are flat on both sides and provide an offset that lifts the 2nd conductor up so it can be run directly over the 1st conductor. Finding these in your local electrical supply house is rare. You can order them, but min. quantities apply.

The other issue is space. The starter likely has a plastic flange that eliminates the possiblity of the B+ lug from contacting the adjacent motor run stud. This flange now limits the wires angle of attack to 180º, some of which is fouled by the starter motor itself and/or the engine block.

Installing the 2/0 B+, a 10 AWG feed for the engine start and run controls and the new 6 AWG conductor for the DC-DC to the stud may be doable, but messy.

What about the 75 Amp alternator output (4 AWG?) conductor that you previously said was connected to the starter? That would make 4 lugs within 180º.

I just don't see the need to stack lugs on the starter when both the alternator and the DC-DC should be directly connected to the battery. Easily accomplished with the use of a couple of MRBF fuses in a dual fuse block, no lug stacking required.

Where else are you going to fuse the DC-DC and the alternator?

[newhaul]

Originally Posted by Putt-Putt

Well, thats different now. The DC-DC's positive input terminal is now connected to a battery, otherwise the engine could not start.

In my mind stacking the lugs of high current circuits on to the starter lug is never a good idea. How many are on there now 3, 4, more?

If it was me I would move the alternator and the DC-DC to the batteries or better yet, a positive busbar.

Regardless, have a good time installing your 4th backup charge source in this often grey and windless environment.

This is spare engine at my shop on the starter lug for battery connectivity is
1 the battery cable a 2/0 , another one simulating the dc2dc, the 10 agw wire from alternator, the main ignition feed wire, and the 10agw wire that goes to the glow plug relay.

There are still threads after the nut so what is the problem? Only one actually interacts with the starter and that is the battery cable .
The rest are just using the lug to make connections.

For reference the extension is 3 inches long so the alternator wire can be as short as 6 inches to comfortably be routed.

[CaptainRivet]

Originally Posted by newhaul

This is spare engine at my shop on the starter lug for battery connectivity is
1 the battery cable a 2/0 , another one simulating the dc2dc, the 10 agw wire from alternator, the main ignition feed wire, and the 10agw wire that goes to the glow plug relay.

There are still threads after the nut so what is the problem? Only one actually interacts with the starter and that is the battery cable .
The rest are just using the lug to make connections.

For reference the extension is 3 inches long so the alternator wire can be as short as 6 inches to comfortably be routed.

I agree with Tusstuss, conventional lugs are not 100% flat on the other side top side you connect the next one. That means they have only contact on some spots and if you are unlucky the contact space is quite small. Doesn't matter how much you wrench it down that contact space is not getting bigger and you get a connection that's heating up. If you do that more then ones you will have several of that heating up spots on that connection and the first one gets much more heat then it would from its own as more current is flowing. With your 70A that won't create a fire, just unnecessary voltage drop, but if you do that on a 200A+× and first lug has a bad connection due to this it would.
Stacking lugs are made for and to avoid this as tusstuss explained well and you have a best example use case where they should be used.

[newhaul]

Originally Posted by CaptainRivet

I agree with Tusstuss, conventional lugs are not 100% flat on the other side top side you connect the next one. That means they have only contact on some spots and if you are unlucky the contact space is quite small. Doesn't matter how much you wrench it down that contact space is not getting bigger and you get a connection that's heating up. If you do that more then ones you will have several of that heating up spots on that connection and the first one gets much more heat then it would from its own as more current is flowing. With your 70A that won't create a fire, just unnecessary voltage drop, but if you do that on a 200A+× and first lug has a bad connection due to this it would.
Stacking lugs are made for and to avoid this as tusstuss explained well and you have a best example use case where they should be used.

Anyone remember I am retired shipwright with my own shop and equipment.
All of my cables are to be custom purpose made all soldered copper cable ends .
( on all off grid and marine systems I install.)
While on the surface your argument is valid. A properly designed and installed system will always account for and negate all possible negative issues.

[CaptainRivet]

Originally Posted by newhaul

A properly designed and installed system will always account for and negate all possible negative issues.

Exactly. So check if you have heat or voltage drop, if yes change the lugs when you have time.

I am learning everyday and won't stop till i die...means a complex system like on boats is designed to your or my or other installers best ability, what you don't know you cannot take account for. Thats what regulations like ISO and AbYC are originally made and used for. Today its missused and overly complex to deny responsibility and insurance coverage...sadly.

[sailingharry]

Originally Posted by newhaul

This is spare engine at my shop on the starter lug for battery connectivity is

1 the battery cable a 2/0 , another one simulating the dc2dc, the 10 agw wire from alternator, the main ignition feed wire, and the 10agw wire that goes to the glow plug relay.



There are still threads after the nut so what is the problem?

Putting aside safety for a moment, ABYC puts a hard limit of 4 terminals, and you have 5. And we all know that if you are not abyc compliant your boat will sink while burning and insurance won't cover it. So that's halfway decent reason to limit the four right there.

From the safety aspect, I don't fully agree with abyc, captain rivet, or tustus. My problem in general is absolutes.

I don't know why if abyc allows four, the fifth one is horrible. I also can't see overloading/overheating if your first is the starter cable (likely the most powerful cable on your boat), the second is the alternator (typically much lower current), and the next 10 are low current devices like engine instruments.

All that said, I personally hate multiple terminals on a single stud. It just gets so messy. I recently had to remove the starter on my i/o. Could barely reach it to begin with, and there were three terminals on the starter. What a dog to get them all back on again when I was putting it together.

But on the flip side, I am pretty sure that my four 200Ah AGM batteries have individual cables to a single terminal block, and then a fifth cable going on to distribution. Putting aside fusing issues (which I'm not terribly happy with), I think adding bus bars to reduce the terminal count would have made a messier installation in the limited workspace available. While in theory there might be heat issues, in practice my highest loads are under 200A (.25C) and those tend to be intermittent.

[CaptainRivet]

@sailing harry: the limit is 4 because long term experience of dozen installers involved in creating this regulations saw in reality that due to added serveral factors, raising resistance is main, from 5 lugs the problems arrising.
You simply have to set somewhere a limit. And yes as always there will be exceptions where at 3 lugs the boat is burning down while someone else stacked 10lugs running 250A and all is ok.
And no my starter or alternator cable is not the biggest...on my cat there are dozen that are bigger and the inverter cables are the biggest ones, on my mono it was a 13m long 240sqmm cable that ran a bowtruster made for a 18m on a 12m longkeeler ketch and sucking cont 800A out of the batteries (bought ketch like this)