Question about Current flow through Alternator

[teneicm]

OK, hopefully this won't be too confusing!

My existing set up has one wire from the alternator feeding back into the starter motor which then sends current back to the battery to recharge when the alternator/engine is running. Also have one large (0 gauge) wire coming out of the alternator to a battery isolator diode which then goes on to the house bank. Coming to the same terminal on the battery isolator diode as the alternator wire is the main wire from the battery charger that runs off the generator. I'd like to do two things: First, move the main charging wire from the battery charger to connect directly to the house the bank. Then, I'd like to remove the large gauge alternator wire from the isolator and instead insert an ACR between the alternator and the house bank. In theory, I think this would allow my battery charger to also charge my start batteries, and also the ACR would keep them separate when no charge source exists. My question is this: When charging with the generator driven battery charger, will current flow from the battery bank (through the ACR) and then through the alternator and on to the start motor, back into the start battery? Or does the alternator not being on "block" the current from passing through?

Hopefully this makes sense....

Cheers- Matt

[phorvati]

Originally Posted by teneicm

OK, hopefully this won't be too confusing!

My existing set up has one wire from the alternator feeding back into the starter motor which then sends current back to the battery to recharge when the alternator/engine is running.

Dont think of it as wire going back into the starter motor, it goes to the Starter Motor terminal. When engine is running, charging current will not go into the starter motor. Charging current from your other device will not go into the non-spinning alternator. It will go into your battery via the other cable.
Not familiar with ACRs but if your banks are house and starting, then your starting bank only needs a trickle charge, few % of the amount of charge you need to put into your house.
While you're at it, consider completely separating the house from starting bank, and getting rid of isolating diodes.
My starting bank is completely separated from the house and wired only to starting battery via 150amp ANL fuse. Starting battery is < 10" round trip from starter motor. Negative goes back from starter motor housing to starting battery only.
I charge that starting battery via auxiliary terminal on one of my charge controllers. This is 6 feet away from starting bank but its ok, since only few amps flow through it. In my case it happens to be solar controller.
You can achieve the trickle charge needed for the starting bank via echo charger or aux. terminal on any of the chargers that have it. It has to be able to limit the current to trickle charging.

[smac999]

first of all, whoever did you diode setup was an idiot. your engine battery is going to drain into your house battery when your house battery voltage drops 0.7v lower then your engine battery. they did a hack job used the diode block, trying to add it to and existing setup instead of making the whole thing right. which would have disconnected the original alternator cable between the alt and starter.

I would get rid of it.

how big is your alt? if it's not the big. like 80a or less. I would just leave the alt cable going to the starter. and just connect an acr between the 2 battery pos posts if they are close together. do not use the alt as a junction point, it will work but it just makes things confusing. the acr goes between the 2 batteries. and get rid of the diode block and cable to house battery. and connect the battery charger to either battery. which ever one is easier. it will charge both batteries through acr.

if the alt is bigger, then I would run a cable direct from alt to house bank and remove the one from alt to starter. and same thing, put acr between the 2 batts.

acr wires, charger wire, and alt wire should all be fused near the batteries

[smac999]

Originally Posted by phorvati

While you're at it, consider completely separating the house from starting bank, and getting rid of isolating diodes.

umm that's what the isolator diode does. (when properly wired)

My starting bank is completely separated from the house and wired only to starting battery via 150amp ANL fuse. Starting battery is < 10" round trip from starter motor. Negative goes back from starter motor housing to starting battery only.
I charge that starting battery via auxiliary terminal on one of my charge controllers. This is 6 feet away from starting bank but its ok, since only few amps flow through it. In my case it happens to be solar controller.
You can achieve the trickle charge needed for the starting bank via echo charger or aux. terminal on any of the chargers that have it. It has to be able to limit the current to trickle charging.

what you wrote doesn't make any sense...

but if your engine battery is only charged from solar? this is fine for sitting at the dock. but while motoring it needs to be charged from the engine alt. otherwise you'll get to have a stalled and dead engine while motoring.

and if your negs are isolated between the house and eng battery nothing is going to be charging too well..

[Maine Sail]

An ACR or combiner is wired between two battery banks but NOT in the alternator output wire.. Your current isolator wiring, as I read it, is completely botched.. Best to start over and clean up the issues...

[teneicm]

Originally Posted by smac999

your engine battery is going to drain into your house battery when your house battery voltage drops 0.7v lower then your engine battery.

Just curious, how would that work and what would the path be? Does the diode open up once there is a .7v differential?


The alternator is small- only 40 amps. What if I left the small wire back to the starter motor intact, but also moved the larger wire directly to the house bank and then installed the ACR between the house and the start battery? When the engine runs, current flows both to the house (via the larger wire) and the start battery (via the smaller alternator wire and start motor post). When the engine is off, the ACR prevents the batteries from combining. When the generator/battery charger runs, the ACR opens and current flows from the house to the start battery. Sound right?

[Dsanduril]

Originally Posted by teneicm

Just curious, how would that work and what would the path be? Does the diode open up once there is a .7v differential?

It's simply a characteristic of diodes. Diodes are semi-conductors, and it takes a little juice to make them conduct. A diode has a forward Voltage, which is the amount of Voltage lost in the diode when allowing current to flow. Different diodes have different forward Voltages, but somewhere around half a Volt is typical. Diodes consume power (that ~half Volt times the current you are putting through them), which is why they are installed on heat sinks. Unless you need a 20W heater in your engine/battery room....

The reason their use in the way you described is a problem is that the batteries will see different voltages when charging. If the starting battery is seeing 14.4 Volts then the house bank will only see about 13.8 because of the diode and never get a full charge. On the other hand, if your Voltage regulator is sensing from the house bank then when it is at 14.4 the starting battery will see 15 and get overcharged.

So, the ACR solution you are suggesting is suitable. If you replace the diode with the ACR you should get the same results from the alternator. Do the two wires from the alternator come from the same output post? If so then the starting battery will charge from the generator as well (battery charger to ACR input, to alternator post to starter post to starter battery). Do they come from different posts on the alternator (it would seem odd to have dual-output on a 40A alternator)? In that case would need to know if it is a dual-output alternator with isolation, in which case you would not get a charge from the generator (but if it is built that way then why would you need the external diode).

I would, however, suggest that you wire both the charger and the alternator to the house bank, then run a wire from there to the ACR and thence to the starting battery. If you put the ACR where your current diode is described and the ACR fails to close (electrical devices close to allow current flow, open to stop flow) then only the starting battery will get charged.

[skipmac]

Here is a simplified description for what many consider the best way to set up batteries and charging.

1. All charging sources (alternator, battery charger, solar, etc) connect to the house battery banks. This is where most power is used so where most power needs to go back.

2. Starting battery should be isolated from the rest of the system. Best way to charge this battery is to use a combiner like the ACR from Blueseas or one of the Yandina combiner models.

3. Get rid of the diode as it reduces charging due to the voltage drop.

4. Don't forget to properly fuse everything.

[Dsanduril]

A picture (even crude) being worth a thousand words, I think we're mostly saying...

Wiring.PNG Views: 291 Size: 24.2 KB ID: 70049" style="margin: 2px" />

Can you confirm that the "current setup" is what you have?

[cal40john]

Originally Posted by teneicm

Just curious, how would that work and what would the path be? Does the diode open up once there is a .7v differential?


The alternator is small- only 40 amps. What if I left the small wire back to the starter motor intact, but also moved the larger wire directly to the house bank and then installed the ACR between the house and the start battery? When the engine runs, current flows both to the house (via the larger wire) and the start battery (via the smaller alternator wire and start motor post). When the engine is off, the ACR prevents the batteries from combining. When the generator/battery charger runs, the ACR opens and current flows from the house to the start battery. Sound right?

The ACR is doing nothing. If your start battery is connected to the starter, and the starter is connected to the alternator, and your alternator is connected to the house bank, then you have made a short that is the same as wiring the two batteries together at their posts.

You have to take off the wire between the alternator and starter.

You don't need to re-invent the wheel, others have made this as simple as it's going to get
Google Image Result for http://bluesea.com/files/resources/newsletter/images/acr_wiring_diagram.jpg

The battery switch that allows you to start the engine from the house bank in an emergency is the only thing that isn't absolutely necessary to make the charging work properly.

[a64pilot]

Pardon my ignorance and this question is actually meant to educate myself as opposed to helping the OP and I apologize if it's a stupid question.
Would it be best "ideally" to have two alt's, leave the small one connected to the starting battery and install a larger, higher output Alt and connect it only to the house bank and leave those banks entirely separate?

[teneicm]

Originally Posted by Dsanduril

A picture (even crude) being worth a thousand words, I think we're mostly saying...

Attachment 70049

Can you confirm that the "current setup" is what you have?

Yes, this pretty much has it. The only one complication is that we have a cat, so 2 alternators and 2 start batteries. Both alternators come into the same isolator (the isolator has 2 terminals for charging sources and 3 terminals for different battery banks). Is there any issue with having both alternators connected directly into the house bank?

[Dsanduril]

Given appropriate fusing in all the wiring, no problem connecting both alternators (and the charger) to the house bank. However, you'll need two ACRs (or a dual output one) to keep the starting batteries separate. Otherwise you'll have both starting batteries connected together.

[phorvati]

Originally Posted by smac999

umm that's what the isolator diode does. (when properly wired)



what you wrote doesn't make any sense...

but if your engine battery is only charged from solar? this is fine for sitting at the dock. but while motoring it needs to be charged from the engine alt. otherwise you'll get to have a stalled and dead engine while motoring.

and if your negs are isolated between the house and eng battery nothing is going to be charging too well..

I'm not on the dock. What does dock have to do with anything?
Starting battery gets depleted VERY little during starting, unless you use it for purging air or priming diesel fuel lines.

100 amps for 15 seconds = 0.41 AH,
so to put that back it takes
0.4 Amps for 1 hour.
So any trickle charger will keep your starting bank happy. If you can set it up to automatic so you don't have to think about it, thats the best. Starting bank does need to be charged during engine runtime, and it does not need to be charged from the alternator.
I probably put at least 5AH every day into starting bank via aux. solar charger regardless of if i started the engine or not. So my starting bank has been happy for a decade or so. I've changed it once.

The problem is if you start your engine numerous times over a long period of time and don't put any AH back.

[SVNeko]

Originally Posted by Dsanduril

Given appropriate fusing in all the wiring, no problem connecting both alternators (and the charger) to the house bank. However, you'll need two ACRs (or a dual output one) to keep the starting batteries separate. Otherwise you'll have both starting batteries connected together.

As someone dealing with the same issue and being less than technical, a diagram of the catamaran setup would be a godsend.