24v Batteries.. Series or Parallel First?

[Fuss]

Originally Posted by Pelagic

I of course fully charge on passages by motor sailing for a while (230amp 24v alternators) when the autopilot loads are heavy.

I am now installing 4 x 327W Sunpower Panels and switching the many original halogen and incandescent reading and engine room lights to LED, so it will be interesting to see what my new consumption levels are.

Thanks all for your advice on sorting this out.

Sounds good.
4 X 327w is alot of solar and will probably make your generator obsolete.

I have 400w of solar and a propshaft alternator which makes my generator obsolete. I only run it for maintenance and backup even though I have no gas onboard.

[Pelagic]

Originally Posted by Fuss

Sounds good.
4 X 327w is alot of solar and will probably make your generator obsolete.

I have 400w of solar and a propshaft alternator which makes my generator obsolete. I only run it for maintenance and backup even though I have no gas onboard.

I am trying to make my Northern Lights Gen (10kw) non critical by switching to a DC water maker and LED’s, so that if the gen is down, I only loose the air cons which is no big deal.

Fuss I am interested in your shaft generator as Stargazer is fitted with one but the previous owner said they could never get enough RPM from free-wheeling under sail to justify keeping it connected.

I have thought of switching to a low RPM Permanent Magnet Alternator, but focused on the Solar first which is a passive solution

How do you do your prop shaft generator?

[Fuss]

Originally Posted by Pelagic

I am trying to make my Northern Lights Gen (10kw) non critical by switching to a DC water maker and LED’s, so that if the gen is down, I only loose the air cons which is no big deal.

Fuss I am interested in your shaft generator as Stargazer is fitted with one but the previous owner said they could never get enough RPM from free-wheeling under sail to justify keeping it connected.

I have thought of switching to a low RPM Permanent Magnet Alternator, but focused on the Solar first which is a passive solution

How do you do your prop shaft generator?

Sorry for the late reply.
I would keep the existing watermaker and run it off the inverter.

There can be alot of reasons why propshaft alternators don't work, boat too small (needs 45+ feet), wrong ratio, wrong alternator, small prop, wrong gearbox.

The propshaft alternator install looks good and very promising, the ratio looks around 6:1 is that right?

Do you have a 3 bladed fixed prop?
Is your cutlass bearing in good condition?
Does the gearbox accept a side load and is it hydraulic so that the prop always spins or does it stop spinning when put into astern.?

Advantages of an alternator over a pmm is that you can switch it off, easily regulate it and that it makes amps while motoring as well over the full rev range, effectively acting as an extra alternator.
Disadvantage is that it takes amps to run (about 2 for this one I think as it looks small)

At what alternator revs does this alternator start producing amps? it needs to be around 1000. Also what are the specs... amps at 24v?

At what speed do you stop sailing and start motoring?

Can you "normally" do 5.5kts+ ?

[Pelagic]

Wow!! my turn to apologize as I had to put my boat refit on hold to do an overseas project. Back to work on my boat again.

my answers below

Originally Posted by Fuss

Sorry for the late reply.
I would keep the existing watermaker and run it off the inverter.

There can be alot of reasons why propshaft alternators don't work, boat too small (needs 45+ feet), wrong ratio, wrong alternator, small prop, wrong gearbox.

The propshaft alternator install looks good and very promising, the ratio looks around 6:1 is that right? Yes

Do you have a 3 bladed fixed prop? Yes
Is your cutlass bearing in good condition? Yes...turns easy by hand
Does the gearbox accept a side load and is it hydraulic so that the prop always spins or does it stop spinning when put into astern.? Intermediate Bearings prevent side load...Always spins

Advantages of an alternator over a pmm is that you can switch it off, easily regulate it and that it makes amps while motoring as well over the full rev range, effectively acting as an extra alternator.
Disadvantage is that it takes amps to run (about 2 for this one I think as it looks small)

At what alternator revs does this alternator start producing amps? it needs to be around 1000. Also what are the specs... amps at 24v?

At what speed do you stop sailing and start motoring? >5knts

Can you "normally" do 5.5kts+ Yes ?

[rwidman]

Originally Posted by Andina Marie

In real life, as opposed to theoretical hypothesizing, and in contrast to many published authorities, it matters very little what path the connections take. It is more important to use an adequate wire gauge.......

I agree. The second drawing of the two is simpler and less likely to get screwed up at some future date. Take the power off wherever it is convenient. Use the largest cable you can find/afford. Use proper connection techniques. Many vendors will attach the lugs for you if you buy the cable and lugs from them.

[rwidman]

Originally Posted by sailinglegend

If you search these forums you will find that Maine Sail has done just this and proved that the cable connection position does matter. I guess he hasn't responded because he has got bored arguing with you and goboatingnow.

As he and others repeatedly post ALL manufacturers recommend connecting the cables in such a way as to balance the loads on each battery.

It's easy to rig a test to get the results you want. Or set it up incorrectly in the first place. We are talking very short runs of very large cable here. The resistance (if constructed correctly) is negligible. If you were to scatter the batteries all over the boat, the wiring sequence would make a bigger difference.

[CharlieJ]

Remember that the 12 volt (nominal) "battery" is really 6 x 2 volt (nominal) cells in series.

[bobcat22]

Originally Posted by Fuss

Myself, I would not be changing anything. It is important to have the same sized (length and thickness) cables between the series connections and the same sized cables between the parallel connections, but that's standard.

The cabling in some of the above diagrams looked far too complicated and messy.

The method 2 diagram looks along the right lines to me.

I would not recommend the smartgauge ultimate solution as it is far too complicated as a realworld solution.

The whole thread came about as an electrical engineer talked about improved charging by changing interconnects from series first to parallel first.....

What is your absorbtion voltage set to and for how long and what is the recommendation of the battery manufacturer?

This is old, but as new people take a look (like me), it's nice to clarify. It is required to have adequate cable diameter and reducing resistance is useful to a point. However, you DO NOT need to have all the cable lengths the same in a series string. Make them all as short as you can. For example, if the B+ needs to be longer than the B- don't artificially lengthen the B-.

This is different in a parallel block of more than two cells. The connection between cells or batteries paralleled need to have the same resistance otherwise the cell or battery with less resistance will get discharged faster causing increased cycling of that one versus the other(s) and life shortened.

In terms of parallel first or series first, parallel first then series. This will improve reliability and battery life. If you have a bad cell in a parallel circuit, the voltage stays the same but only the capacity is reduced for the bank. The same bad cell in series would reduce bank voltage and reduce lifetime. There is a recent paper on this done showing a bank wired series first has only 75% of the life of parallel first. That's a big deal and might be the difference in some people getting 8 years out of their bank versus others only 6.

A simple way to think about this many will wire 6V batteries for a 24V tank with 2 series of 4 in parallel. This is 4 in series (4S) then two paralleled (2P) or 4S2P in bater lingo. The alternative is to parallel them in pairs first (2P) then string in these pairs 4 series (4S) or 2P4S. both are 24V and both use 8 batteries.

The advantages of parallel first include the above but also that it may be easier to parallel a pair or few batteries with short low resistance connectors and then string those pairs together with the others with the minimum but perhaps varying length connectors as may be required. Thats no problem for the series.

[leandro.freire]

Originally Posted by bobcat22

In terms of parallel first or series first, parallel first then series. This will improve reliability and battery life. If you have a bad cell in a parallel circuit, the voltage stays the same but only the capacity is reduced for the bank. The same bad cell in series would reduce bank voltage and reduce lifetime. There is a recent paper on this done showing a bank wired series first has only 75% of the life of parallel first. That's a big deal and might be the difference in some people getting 8 years out of their bank versus others only 6.

Can you share this paper with the rest of us?