Battery Charge Alarm

[donradcliffe]

Maine Sail can draw another diagram with an ACR in the circuit which will show EXACTLY the same difference between the battery voltages. The issue in his diagram is the difference the the VD on the charging wires to each battery, not the VD across the splitter vs the ACR.

[hellosailor]

Excellent point, Maine. What isn't expressly clear from the diagram, is that the final cable run to the house bank is apparently WAY UNDERSIZED, causing the significantly higher voltage drop under high loads, as compared to the cable run to the starter battery. If that undersized cable run was measured, and could be reasonably replaced with a heavier gauge cable, that one new piece of "proper" cable might be all it took to balance the two voltage drops at high house bank loads. Although, of course, that would still only "balance" the runs at a certain point, leaving them unbalanced at other times anyway, an inherent flaw in the design.
A situation better avoided by a battery combiner or echo charger.


It is good to know that former Soviet aerospace electronics designers have apparently found productive employment in recreational yachting industry!

[kas_1611]

Originally Posted by hellosailor

Excellent point, Maine. What isn't expressly clear from the diagram, is that the final cable run to the house bank is apparently WAY UNDERSIZED, causing the significantly higher voltage drop under high loads, as compared to the cable run to the starter battery. If that undersized cable run was measured, and could be reasonably replaced with a heavier gauge cable, that one new piece of "proper" cable might be all it took to balance the two voltage drops at high house bank loads. Although, of course, that would still only "balance" the runs at a certain point, leaving them unbalanced at other times anyway, an inherent flaw in the design.
A situation better avoided by a battery combiner or echo charger.


It is good to know that former Soviet aerospace electronics designers have apparently found productive employment in recreational yachting industry!

Without being able to check the dimension of the cables on my boat how do we know the house battery cable is Way undersized?

[Maine Sail]

Originally Posted by donradcliffe

Maine Sail can draw another diagram with an ACR in the circuit which will show EXACTLY the same difference between the battery voltages. The issue in his diagram is the difference the the VD on the charging wires to each battery, not the VD across the splitter vs the ACR.

Of course a competent installer would not install an ACR in the alternator B+ / output wire. They would direct run the alternator to the house bank and bridge the start and house banks, between their positive terminals, with the ACR. Now the ACR is carrying only the start bank load, seeing the v-sense corrected target voltage from the house bank and only small start bank current needs to flow through the ACR.

Diode idolaters, by design, are intended to be installed in the alt output wire. An ACR should bridge battery bank directly to battery bank and not alt or alt feed wire to battery. Most diode isolators I have come across are installed incorrectly by being closer to the alt than where they should be. Ideally they should be installed closer to the bank for more accurate voltage sensing and less issues with voltage drop..

We recently chartered a catamaran and the diode isolator was in the engine room with the self sensed Hitachi alternator. The batteries had massive distances between the isolator and the banks. Needless to say the charging system performed horribly... When we returned the boat I asked the charter company owner how often they replaced the batteries on that boat. They had replaced them every 11 - 12 months for the previous 3 years.... No kidding..... Eight golf cart batteries murdered in 11 - 12 months because of a horribly designed charging system....

[Maine Sail]

Originally Posted by hellosailor

Excellent point, Maine. What isn't expressly clear from the diagram, is that the final cable run to the house bank is apparently WAY UNDERSIZED, causing the significantly higher voltage drop under high loads, as compared to the cable run to the starter battery.

You would be shocked at how undersized much of the alternator wiring is out there. Most folks tend to size for 3% voltage drop but never account for fuses, terminals, switches etc.. A 3% voltage drop at 14.4V makes the battery only see 14.0V and can really hinder your recharge performance. A 3% voltage drop is pretty unacceptable if you want a high performance charging system.

They also often size wires individually as opposed to the entire circuit length: (I had to have a customer explain to me how he got to 8GA wire for his 120A alternator)

"Let's see the positive wire is 6' and will carry about 100A at most so if I want to be close to 3% I need 8GA. The negative is also 6' and will carry 100A so if I want 3% I need 8GA. Yep 8GA it is....."

So he happily wired the system with 8GA except his "circuit" was 12' of 8GA. Of course 12' of 8GA at 100A is more than a 6% drop and we've not yet included any terminations, fuses etc....... It is not at all unusual for me to measure more than a 10% voltage drop in charging systems....

[hellosailor]

k-
Rashly assuming that Maine's diagram accurately reflect your problem (and that situation is what I commented on) then you can see a voltage drop under load of 0.66V (at 6OA) to the house bank, versus a drop of 0.04V (at the lower amperage drawn there) to the starter battery.


A rough number, as examples not as specifics for here:


If the house battery final run was #2AWG copper, and the total circuit loop was 30' long (ground included).
It has a resistance of 0.1808 Ohms Ohms per 1000 feet.
And if the alternator was putting out 16 volts (round number) that cable alone would cause a voltage drop of 0.656 volts, a loss of loss at 4.11% for the circuit at a 60 Amp load.

Simply replacing that with a much heavier cable like 4/0 AWG (which is THICK) would reduce the voltage loss from 0.6V to less than 0.1V.


So "simply" replacing the cable with a substantially thicker one, can change the voltage loss significantly and "balance" the two circuits--at a some specific load point. But that kind of approach still only targets one load point. It can cost a fortune to run cables that thick. Installing a true battery combiner can be much cheaper and simpler. (Although, I'd still take a look at the cables and make sure they were an adequate size.)

[kas_1611]

Something else to add to the list of things to check then

Is there an easy way to determine what size cables you have fitted without having to disconnect them, cut off any connectors and physically measure the cross section of copper?

External diameter would give you a rough idea but unless you know the thickness of the insulation you can't be sure of the copper diameter inside. And I bet no one thought to put the size in simple lettering on the outside of the insulation did they

There are some hefty looking cables in the system, some are as thick as my finger and one or 2 are thick as my thumb. Not that this really helps as I have thin fingers but it does give a simple indication.

Presumably they are sufficient to do the job so by doing a basic swap out of the isolator for a smarter combiner there would be no major issues but if I were to increase the size of the cables it would improves matters greatly. Just is it worth the cost and hassles to run thicker cables from the engine bay, round the cabins and into the house bank? Or is it worth just making the cable from the alternator to the splitter thicker (or doubling up)?

Keiron

[transmitterdan]

Most quality wire will have the size of the wire (mm or AWG) hot stamp marked on the insulation jacket. It will repeat every so often to make finding it easier.

Smart combiners usually specify how to size the cables for proper operation. Before buying a specific model download and read the installation instructions. They may require a min/max size/length of the cross connect cable(s). Usually the important cable is the one going from the combiner to the start battery. The voltage drop in this cable isn't too important and may actually help reduce current surges when the combiner connects the banks together.

Even if the instructions for the combiner don't seem logical follow them anyway. If any doubt come back here and ask.

[kas_1611]

Originally Posted by transmitterdan

Most quality wire will have the size of the wire (mm or AWG) hot stamp marked on the insulation jacket. It will repeat every so often to make finding it easier.

Smart combiners usually specify how to size the cables for proper operation. Before buying a specific model download and read the installation instructions. They may require a min/max size/length of the cross connect cable(s). Usually the important cable is the one going from the combiner to the start battery. The voltage drop in this cable isn't too important and may actually help reduce current surges when the combiner connects the banks together.

Even if the instructions for the combiner don't seem logical follow them anyway. If any doubt come back here and ask.

Dan, thanks for that. I have had a close up look at the photos I took of the electrical cables and I think I can see a size marking on at least one of them which reads 1x10. 10mm cross section would appear to fit.

I will try to get installation guides before I purchase and have contacted manufacturers to start discussions on what would work with my system. If I still have any concerns I'll get back to picking the communal brain

Cheers

Keiron

[kas_1611]

As the Admiral is still onboard I asked her nicely if she could take a look in the engine bay for any signs of numbers on the wires. She managed to find 2 sets on the positive wires leading into the isolator which read:
TF Kable 3 BBJ HAR H07V-K and another as 0052M

A quick google and the H07V-K reveals the wires are DIN VDE 0281-3 and BS6004 rated for up to 750vDC (1000vAC) usage between -30ºC and +70ºC. I've downloaded the product manual and I'm 98% sure the cables are 50mm2 but just to be safe I am going to assume right now they are the 35mm2 versions.

The 35mm2 are 10mm diameter (not sure if that is insulation OD or copper OD) and have a resistance rated at 0.554Ohms/km. The 50mm2 are 11.8m diameter and 0.386Ohms/km. The manual I have for the Pro Split R indicates for 115amps 35mm2 is good for up to 1.5m and 50mm2 for 1.5-4.0m. So hopefully this should mean the cables we currently have should be thick enough but I will not be completely sure until I get home with the calipers and the tape measure.

Could the 0052M indicate 00AWG and 52mm2?

Keiron

[donradcliffe]

There is often a cross-connect switch which allows you to parallel the start and the house battery. If your boat has one, you could eliminate the voltage difference between the batteries. Leaving it closed would also increase the effective size of your house bank and make it last longer.

[hellosailor]

"The 35mm2 are 10mm diameter"
A 35mm^2 cable would be about 6.5mm thick, because only the bare wire is measured. The insulation material and therefore thickness can vary, the wire size itself won't. That would be equal approx. to a US #2AWG cable.

A cable that was actually 10mm in diameter (10.4mm) would be an 85mm^2 cable, equal approx. to a US 3/0 (also called "000") cable, very different.

So the question would be which one you have, and how long the cable run is.

If the insulated wire itself is 10mm thick...that would make it the 6.5mm cable, similar to a US #2AWG.

Just to confuse things, our auto industry (and some cheaters in the marine industry) use the Society of Automotive Engineers (SAE) wire sizes, which are about 15% smaller than AWG wires of "the same" numbers.

[Sun and Moon]

Originally Posted by Maine Sail

Of course a competent installer would not install an ACR in the alternator B+ / output wire. They would direct run the alternator to the house bank and bridge the start and house banks, between their positive terminals, with the ACR. Now the ACR is carrying only the start bank load, seeing the v-sense corrected target voltage from the house bank and only small start bank current needs to flow through the ACR.

Diode idolaters, by design, are intended to be installed in the alt output wire. An ACR should bridge battery bank directly to battery bank and not alt or alt feed wire to battery. Most diode isolators I have come across are installed incorrectly by being closer to the alt than where they should be. Ideally they should be installed closer to the bank for more accurate voltage sensing and less issues with voltage drop..

We recently chartered a catamaran and the diode isolator was in the engine room with the self sensed Hitachi alternator. The batteries had massive distances between the isolator and the banks. Needless to say the charging system performed horribly... When we returned the boat I asked the charter company owner how often they replaced the batteries on that boat. They had replaced them every 11 - 12 months for the previous 3 years.... No kidding..... Eight golf cart batteries murdered in 11 - 12 months because of a horribly designed charging system....

Maine,
Is the ACR smarter than a diode? Can it put the start battery on float when the rest of the system is on bulK? I guess I'm wondering why the start battery doesn't get overcharged when the house bank is receiving a bulk charge. Or maybe the depleted house bank pulls the input voltage down during bulk charge so the ACR doesn't turn on? I'm hoping you can clarify for me.
Thanks!

[transmitterdan]

The ACR is a pretty simple device. It has 2 states, on and off. When the house bank charger begins to charge then the ACR automatically goes to the on state and it puts the start and house banks in parallel. Thus all batteries are getting the same charging "mode". So they all go into float mode at the same time. When there is no charging source the ACR automatically turns off and the two banks are no longer in parallel.

There are different ACRs on the market. Some of the early models were "dumb" and sometimes got into a condition where they switch on and off too often. Most newer models have solved this problem.

[Maine Sail]

Originally Posted by transmitterdan

There are different ACRs on the market. Some of the early models were "dumb" and sometimes got into a condition where they switch on and off too often. Most newer models have solved this problem.

Relay cycling happens when the much smaller start bank is fed the charge source/current first. Due to its high SOC comes up to voltage almost instantaneously then combines with a much larger & depleted house bank which pulls combine voltage back down and results in what is commonly referred to as "relay cycling". The smaller the charge source eg: solar, wind or hydro the more problematic relay cycling becomes if the sources feed start first. If you feed charge sources to house bank first it eliminates this nuisance cycling and also means you are passing minimal current across the relay and will have minimal to no voltage differences between banks..