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Old 19-12-2010, 10:07   #16
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Originally Posted by cal40john View Post
If you go to a 3 stage charger that allows the battery to go to a high voltage during bulk phase you're overcharging the start battery that was topped off early on. If you stay with the automotive style regulator it doesn't matter.

John
Not really -- the 13.2v combine set-point allows the house bank to come into the mix well before the start battery is "topped off". At the point they're combined they all act as one bank and the higher voltage battery(ies) will flow charge to the lower ones more quickly so they'll all top-off together. Once they're combined they will act as one system.
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Old 19-12-2010, 10:22   #17
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...
1. ...This should be a fuse with a high ampere interrupt capacity (AIC) like the new terminal type fuses by Blue Sea Systems or an ANL fuse or a Class T fuse.
...
2. An external regulator for your alternator is preferable.
...
3. ...The Magnum ME-SBC would work OK...
Bill
Thanks very much, Bill! You even answered a question I hadn't asked yet but wondered about: what kind of fuse to use. Also, I have an old Alpha alternator regulator; at some point I'll have the alternator modded to use it.

Interesting about the Magnum. I wasn't clear on the difference between it and the Xantrex/Balmar devices... apart from the price, of course.

I want to do all this right, but on a budget, and keeping in mind that we run an extremely simple low-energy ship. I haven't done an accurate daily amp-hour budget yet, but first estimate's under 50ah/24h.
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Old 19-12-2010, 10:29   #18
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Originally Posted by SailFastTri View Post
Not really -- the 13.2v combine set-point allows the house bank to come into the mix well before the start battery is "topped off". At the point they're combined they all act as one bank and the higher voltage battery(ies) will flow charge to the lower ones more quickly so they'll all top-off together. Once they're combined they will act as one system.
As long as the charge voltage is above the battery voltage the current only goes into the batteries.

Yes, what you say can happen. If the house bank under charge is at a lower voltage than the voltage of the start battery standing alone, then when you connect the two the start battery will discharge into the house bank.

John
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Old 19-12-2010, 10:54   #19
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Why do you think an echocharge or duocharge is better than a voltage-sensing relay (combiner)? The latter is more efficient (no voltage drop and no power converted to heat) and simpler, and usually less costly. All are completely automatic.
A battery combiner does just that: it combines the batteries together. If all combined batteries are at approximately the same state of charge (SOC), then the in-rush current from the more-charged battery to the less-charged battery is not a problem. However, consider what happens when you connect a nearly fully charged start battery of about 100AH with a large 50% depleted house bank. There will be an inrush of current -- lots of it -- from the start battery to the large house bank, effectively discharging the start battery somewhat.

Batteries don't like to be discharged rapidly, even start batteries. While they are designed to deliver high amperages, it's only for very short periods. Typically, it takes LESS THAN ONE AMP-HOUR to start the typical mid-size diesel engine. Lots of amps (100-250) but for very short time periods (3-10 secs typically).

When you combine a fully charged start battery with a depleted large house bank -- with no regulation -- you're going to take a heck of a lot more than 1 AH out of the start battery. And fast.

The aforementioned Magnum ME-SBC has a "safety cutoff", so if the amperage in-rush is high it just cuts off until it gets lower. But, it does NOTHING to prevent or ameliorate the in-rush, unless it's below about 30 amps.

Other combiner devices often do NOTHING to prevent or ameliorate large in-rush currents.

By contrast, the voltage-follower devices like the EchoCharge and the Duo-Charge do not actually combine the batteries. Rather, they are one-way devices which bleed off some amperage from the battery bank being charged and deliver it to the start battery. They will not overcharge the start battery no matter the charging voltage on the house batteries. I've tested my EchoCharge voltage while equalizing my house batteries at over 15.5 volts, and found it to be well within the float voltage limits. In other words, it does not pass the 15.5 volts or more thru to the start battery.

The EchoCharge is about the same price as the Magnum "smart combiner", and can pass up to 15 amps...more than enough for the typical setup.

The Duo-charge is more, but it's programmable and can pass up to 30 amps, or more with a relay.

Bill
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Old 19-12-2010, 14:07   #20
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Originally Posted by btrayfors View Post
A battery combiner does just that: it combines the batteries together. If all combined batteries are at approximately the same state of charge (SOC), then the in-rush current from the more-charged battery to the less-charged battery is not a problem. However, consider what happens when you connect a nearly fully charged start battery of about 100AH with a large 50% depleted house bank. There will be an inrush of current -- lots of it -- from the start battery to the large house bank, effectively discharging the start battery somewhat.

Batteries don't like to be discharged rapidly, even start batteries. While they are designed to deliver high amperages, it's only for very short periods. Typically, it takes LESS THAN ONE AMP-HOUR to start the typical mid-size diesel engine. Lots of amps (100-250) but for very short time periods (3-10 secs typically).

When you combine a fully charged start battery with a depleted large house bank -- with no regulation -- you're going to take a heck of a lot more than 1 AH out of the start battery. And fast.

The aforementioned Magnum ME-SBC has a "safety cutoff", so if the amperage in-rush is high it just cuts off until it gets lower. But, it does NOTHING to prevent or ameliorate the in-rush, unless it's below about 30 amps.

Other combiner devices often do NOTHING to prevent or ameliorate large in-rush currents.

By contrast, the voltage-follower devices like the EchoCharge and the Duo-Charge do not actually combine the batteries. Rather, they are one-way devices which bleed off some amperage from the battery bank being charged and deliver it to the start battery. They will not overcharge the start battery no matter the charging voltage on the house batteries. I've tested my EchoCharge voltage while equalizing my house batteries at over 15.5 volts, and found it to be well within the float voltage limits. In other words, it does not pass the 15.5 volts or more thru to the start battery.

The EchoCharge is about the same price as the Magnum "smart combiner", and can pass up to 15 amps...more than enough for the typical setup.

The Duo-charge is more, but it's programmable and can pass up to 30 amps, or more with a relay.

Bill
It doesn't matter how much more discharged one battery is than the other. As long as the charge voltage is above the battery voltages when they are not connected to the source, the current flows into the batteries. Hook the start battery to the charger, current flows into the battery, say the voltage is 13 volts. Hook a discharged battery into this circuit and as long as the voltage doesn't drop does the start battery see anything different? No, so the current continues to flow into the start battery and now also the discharged battery.

John
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Old 19-12-2010, 14:41   #21
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It doesn't matter how much more discharged one battery is than the other. As long as the charge voltage is above the battery voltages when they are not connected to the source, the current flows into the batteries. Hook the start battery to the charger, current flows into the battery, say the voltage is 13 volts. Hook a discharged battery into this circuit and as long as the voltage doesn't drop does the start battery see anything different? No, so the current continues to flow into the start battery and now also the discharged battery.

John
Whenever you parallel batteries of different voltages and state of charge, there will be a flow from the more-charged battery to the less-charged battery. The rate of flow will be largely dependent on the internal resistance of the batteries, particularly the less-charged batteries and, of course, on wire sizes, quality of connectors, and such factors.

AGMs have a very low internal resistance, so can accept a charge at least equal to their amp-hour ratings. They will suck heavily on any charging source ... alternator, generator, battery charger, solar, wind or, in this case, another battery with a higher SOC.

Yes, if the charge voltage is maintained above the start battery's acceptance level, some current will flow into that battery. If you connect a large house battery bank into that circuit by paralleling them, most current will flow from the charging source to the house bank, but current will also flow OUT of the start battery INTO the house battery bank. How much current will depend on the internal resistance of the house battery bank and on the capacity of the charging source. If the charging source is very large in relation to the ability of the discharged AGM house battery bank to accept a charging current, then you're right...it won't make much difference to the start battery. However, this is almost never the case...very few cruising boats out there have enough onboard charging capacity to satisfy a very current-hungry large discharged AGM house bank.

Whatever you believe will happen when you combine less charged batteries with more charged batteries really doesn't matter, since there's really no need to do this anyway. And, IMHO, no reason to risk damaging the batteries over time either by manual switching or by device failure.

Bill
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Old 19-12-2010, 14:41   #22
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Interesting discussion. Bill, you've just about convinced me the echo charge is the way to go.

But back to my original question. I found a diagram I did of the alternator last time I had it out. There are 3 wires connected, labelled 'Output' (red wire), 'AC Tap' (grey), and 'EXC' (I think; purple). There's a fourth stud with nothing on it; I didn't record the label, but in a bad picture I have it might start with INP?

Anyone know if one of those is the volt sense?

Thanks again...
Perry.
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Old 19-12-2010, 14:51   #23
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Perry,

You can find the manuals for Prestolite alternators here:

Prestolite / Leece-Neville Technical Bulletins

Bill
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Old 19-12-2010, 14:56   #24
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Whenever you parallel batteries of different voltages and state of charge, there will be a flow from the more-charged battery to the less-charged battery. The rate of flow will be largely dependent on the internal resistance of the batteries, particularly the less-charged batteries and, of course, on wire sizes, quality of connectors, and such factors.

AGMs have a very low internal resistance, so can accept a charge at least equal to their amp-hour ratings. They will suck heavily on any charging source ... alternator, generator, battery charger, solar, wind or, in this case, another battery with a higher SOC.

Yes, if the charge voltage is maintained above the start battery's acceptance level, current will flow into that battery. If you connect a large house battery bank into that circuit by paralleling them, current will also flow OUT of the start battery INTO the house battery bank. How much current will depend on the internal resistance of the house battery bank and on the capacity of the charging source. If the charging source is very large in relation to the ability of the discharged AGM house battery bank to accept a charging current, then you're right...it won't make much difference to the start battery. However, this is almost never the case...very few cruising boats out there have enough onboard charging capacity to satisfy a very current-hungry large discharged AGM house bank.

Whatever you believe will happen when you combine less charged batteries with more charged batteries really doesn't matter, since there's really no need to do this anyway. And, IMHO, no reason to risk damaging the batteries over time either by manual switching or by device failure.

Bill
They were talking about a combiner that automatically cross connects the batteries above 13.2 volts. Since you normally connect the charge source to the house bank and use the combiner to cross connect to the start battery when the charge source is able to come up to 13.2 volts the start battery isn't going to see a voltage less than its S.O.C. voltage.

John
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Old 19-12-2010, 15:07   #25
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They were talking about a combiner that automatically cross connects the batteries above 13.2 volts. Since you normally connect the charge source to the house bank and use the combiner to cross connect to the start battery when the charge source is able to come up to 13.2 volts the start battery isn't going to see a voltage less than its S.O.C. voltage.

John
John,

Yes, we're working both sides of the same problem :-)

The Magnum device they were talking about is adjustable from 12.8 to 13.8 volts. The default is 12.8 volts. With this setting, it would not connect to the start battery until the charging voltage reached 12.8 or above. You could, of course, set this "connect voltage" higher.

Other combiners, automatic charging relays, etc., may not be adjustable. And, when the charging needs (of, e.g., a hungry AGM bank) exceed the allowable current, these relays may repeatedly open and close. See, e.g.,
Preventing Cycling in Battery Combiners, Voltage Sensitive Relays, and Automatic Charging Relays - Resources - Blue Sea Systems

It's not so much that ACRs and such can't work. Rather, IMHO from a systems perspective there's a better way which avoids some of the potential problems of these devices.

Bill
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Old 19-12-2010, 17:50   #26
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They were talking about a combiner that automatically cross connects the batteries above 13.2 volts. Since you normally connect the charge source to the house bank and use the combiner to cross connect to the start battery when the charge source is able to come up to 13.2 volts the start battery isn't going to see a voltage less than its S.O.C. voltage.

John
That's right.... and the amperage flowing between the charged start battery and the discharged house bank is not going to be high, because the charge source is outputting a much higher voltage than the fully charged starter battery. The charge source is where almost ALL of the charge current will come from. AGM or not.
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Old 19-12-2010, 18:14   #27
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I'm lost now!
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Old 19-12-2010, 23:12   #28
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I'm lost now!
Which part?

No current is going to come out of any battery as long as the applied voltage is above what the battery nominally wants to sit at based on its state of charge. The current will go into the batteries.

Bill points out on his link that there can be a variety of conditions where the combiner will cycle on and off because the current draw will be too high once you add the second battery so the voltage will drop. One example would be a large start bank that is heavily discharged.

John
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Old 28-12-2010, 19:48   #29
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Hi again. I'm back from the boat and newly confused.

The good news: I found the Alternator sense stud, it's not used, so no problem there. But I also found a new red wire from the starter, on the same stud as the alt out (and start batt and house supply). This disappears into a harness that wraps around the engine, connecting with the larger panel harness. On the other side of the engine I found a(nother?) solenoid, with two red wires on one stud. So my theory is that one wire comes from the starter, and the other supplies the panel?

It occurs to me that if I remove the alt out from the starter (or what I was calling the starter solenoid, the cylinder on top of the starter, whatever the heck it is), that other wire will carry only house battery current to the remote solenoid and the panel. They won't 'see' the alternator output, except indirectly via the echo charge current to the house batt.

Could this be a problem in any way? I can't think why, but I'm plumbing the depths of my ignorance here, as my late discovery of this second (?) solenoid should show. I'd really like to understand before I start pulling wires.

Thanks again for any help!
Perry.
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