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Old 18-07-2011, 14:11   #1
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Which Battery for the Bilge Pump ?

I'm working on rewiring my '79 Sabre 34. I now have a pair of T-105's as "the" bank, giving my 225Ah or so for all my needs -- refrigeration, lighting, electronics, and even starting the little Volvo diesel in the morning. I also have a group 32 deep cycle as my "reserve" which mainly serves as balast -- until the day I need it. The reserve bank is about 100Ah or so, is essentially always at full charge (it never sees any loads and is kept charged), and should never be accidentally left to drain down.

My question is my electric bilge pump. I want to connect it (through a small fuse panel) directly to a battery. I can go to the main bank, giving me 225Ah of pumping, assuming my battery is full to start with. Or, I can go to the reserve bank, assuring me of 100Ah of pumping without any risk of a dead battery. Or, I can take a lead off each battery, through suitably sized diodes, and have the full power of both batteries at my disposal, although at a reduced voltage (about .7V drop, if I recall).

Any suggestions? And no, two independent pumps are not currently on my project horizon.

Thanks!

Harry
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Old 18-07-2011, 14:32   #2
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Re: Which battery for the bilge pump?

Connect it to the biggest bank. You want it to be able to run a long time if necessary.
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Old 18-07-2011, 14:55   #3
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Re: Which battery for the bilge pump?

+1 on Daddle's recommendation.

The diodes would cause an unwanted voltage drop to the pump.

Wire directly to the house batteries, with an appropriate fuse near the batteries.

While several people I highly respect (like MaineSail and his collaborators) like the arrangement you have because of its simplicity, i.e., house batteries used for everything and another battery kept in "reserve"), I don't like it very much.

I agree that it's simple. I agree that it can work OK, especially if you have a decent size house battery bank and keep 'em charged, but I think the idea of a "reserve battery" is shortsighted.

Much better, IMHO, is to use the "reserve battery" as a start battery ONLY, and keep it charged with a voltage follower device like an EchoCharge or DuoCharge. This arrangement is still pretty simple....no switching of the 1-2-B-Off battery switch is necessary.

Done right, however, it does add another ON-OFF battery switch for the start battery only. This switch remains in the OFF position except when the engine is in use or is expected to be used, like on a cruise. That, and a hefty ANL fuse in-line located near the start battery provide a good extra margin of safety.

Bill
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Old 18-07-2011, 16:14   #4
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Re: Which battery for the bilge pump?

The main purpose of having a "reserve" or "starting" battery is so that there will always, always be power available to start the engine (and thus drive the alternator, and thus the pumps, etc.), even if the entire house electrical system collapses.

If there's anything else connected to that separate, isolated, single-purpose battery, its purpose is defeated.

So I concur with the previous two posters; power your bilge pump from the big house bank. If that bank ever runs low, you HAVE to start the engine, at which point you'll need the starting battery fully charged.
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Old 18-07-2011, 17:18   #5
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Re: Which battery for the bilge pump?

Quote:
Originally Posted by btrayfors View Post
+1 on Daddle's recommendation.

The diodes would cause an unwanted voltage drop to the pump.

Wire directly to the house batteries, with an appropriate fuse near the batteries.

While several people I highly respect (like MaineSail and his collaborators) like the arrangement you have because of its simplicity, i.e., house batteries used for everything and another battery kept in "reserve"), I don't like it very much.

I agree that it's simple. I agree that it can work OK, especially if you have a decent size house battery bank and keep 'em charged, but I think the idea of a "reserve battery" is shortsighted.

Much better, IMHO, is to use the "reserve battery" as a start battery ONLY, and keep it charged with a voltage follower device like an EchoCharge or DuoCharge. This arrangement is still pretty simple....no switching of the 1-2-B-Off battery switch is necessary.

Done right, however, it does add another ON-OFF battery switch for the start battery only. This switch remains in the OFF position except when the engine is in use or is expected to be used, like on a cruise. That, and a hefty ANL fuse in-line located near the start battery provide a good extra margin of safety.

Bill
Bill,

I know I'm participating in the derailment of my own thread. But here goes....

I understand the basic principles of the "each battery to it's own purpose" philosophy. However, I have yet to understand why the classic 1-2-b-n switch, wired to a house/reserve bank, is short sighted.

In this arrangement, I have a nice big house bank, capable of running my boat. The boat is fairly new to me (just 2 years, but more like 1 season) and the big bank/small bank is basically new this season. However, we spent 8 days on the boat this spring with 4 people, running the refrigeration, with only 3 nights of shore power (agreed, that was a lot), using a 35A factory alternator (new one in the works), and never moved the battery switch. The "reserve" was just that, a fully functional reserve, ready when needed. The house bank ran everything, and then started the engine.

My alternator currently goes through my switch, and I "ignore" my reserve (so it doesn't get charged when under power), but a direct lead to the battery fuse and a battery combiner will be done before the end of August (probably before August).

Benefits of the dual system
* Can't drain the start battery (I can't drain my reserve)
* Can't kill the diodes (I can't either)
* Can't forget to charge the second battery (I can't either)
* You "test" the start battery every day (OK, I can't do that)
* You can combine with the house (I can too, but I can also isolate the spare if it is completely shot)
* It requires no user intervention after turning the switch on (ditto)

Benefits of 1-2-b-n
* All the above
* I can use the reserve in event of a battery disaster (some un-explainable disaster that completely kills my house battery). Granted, it would be VERY scary to have one single 100Ah battery to survive on -- but I can turn my switch to "2" and run cabin lights, running lights, VHF radio, etc. If I were really careful and turned off the fridge, I could even do that for a few days.

So, in all seriousness, what are the disadvantages of the 1-2-b-n switch, and how is the dual system better? I really am open to a discussion here -- I hope I don't sound closed-minded.

Thanks!

Harry
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Old 18-07-2011, 18:34   #6
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Re: Which battery for the bilge pump?

Harry,

Have a look at this basic wiring diagram which illustrates the system you call "dual" (and I call "preferred"):

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Here, you have the complete separation of battery banks as well as the utilization of the right type of battery for the job.....a start battery for starting the diesel and a deep-cycle house battery bank for all other loads.

Deep cycle batteries are not meant to be discharged rapidly. Yes, of course, a 225A deep-cycle bank CAN start a diesel though it's not meant for this purpose. It does so very handily and even better when the batteries are fully charged. In the event of a deep discharge, say to 50% capacity or 12.2 volts, cranking won't be as brisk.

By contrast, starting batteries -- like those in your car -- have thin plates and are designed to deliver a heck of a lot of amperage quickly. This is what the starter likes...lots of amps and sufficiently high voltage to turn the engine over quickly. Faster starts. Less wear and tear over time on the starter, compared to chronic starts with lower voltage. At least that's the theory.

In the diagram above you'll also notice that you haven't given up the ability to use the house bank for engine starting in the event the start battery is compromised. You just switch to position #2 to start the engine.

The EchoCharge shown at the bottom maintains the start battery at full charge....totally automatic. You don't have to switch anything.

So, you leave the 1-2-B-Off switch in the #1 position normally, and only turn on the start battery switch when you need the engine. Simple. Allows disconnecting the start battery from the starting circuit when not in use....a safety factor.

As I said at the beginning, I have a lot of respect for those who advocate the "use house batteries for everything and just keep a spare battery for backup" philosophy. However, I think the solution shown in the diagram is better overall.

By the way, I believe that voltage follower devices like the EchoCharge or the DuoCharge are to be preferred over "battery combiners", since they totally avoid potential problems like bad relays and/or huge inrush currents from the more charged to the less charged batteries.

Bill
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Old 18-07-2011, 20:00   #7
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Re: Which battery for the bilge pump?

Bill,

That is a very interesting wiring diagram. I think I've seen it before (c34 forum, maybe?), but had forgotten about it. The most often touted dual system is the one you drop in from Blue Seas, using their Dual Circuit Plus system. The one you show has some significant advantages, in that you can power either type of load from either or both batteries.

I am not sure I buy your argument about start vs deep cycle. Deep cycle are much better than automotive batteries for a house bank. A real problem is comparing rated values -- Trojan doesn't give CCA, and start batteries don't give Ah! However, I'm not sure I'd rate the CCA of a 2-battery golf cart bank lower than a single Group 32 Start battery. It is also worth noting that many boats have inverters that draw more power than the starter -- on my boat, the starter draws 100A, less than a 1200 watt inverter, and inverters aren't a 10 second load!

I also know of a full time distance cruiser, a motor-sailor with a Perkins 4/236 (that's a horse of an engine!) which has a total of 4 T-105's in two banks -- no "start" battery at all!

Oh, agreed on the "combiner" -- I'm still researching if it will be diodes, VSR, duo-charge, echo-charge, or what. It was a generic term.

Harry
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Old 18-07-2011, 20:42   #8
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Re: Which Battery for the Bilge Pump ?

It's not the average draw of the starter that matters. It's the in-rush current, which typically is MUCH higher and can easily exceed 1,000 amps for about 1/4 second each time you press the start button.

I don't know what engine you have, but my 4-108 draws a heck of a lot more than 100A. When I first put an ANL fuse in line, I blew one with a rating of 250A! The 400A one I've been using for several years seems about right for my engine. One of these days I'll measure the in-rush current.

Meanwhile, it might be instructive to read what Blue Sea Systems says about engine starting in-rush and cranking current, and think about what you're asking heavy-plate deep-cycle batteries to do: http://bluesea.com/viewresource/114

Yes, of course, deep cycle batteries are best for the house bank. I hope you didn't misunderstand me, since this is what I intended. But, little question about it, batteries designed for starting engines are "better" at the task than are deep-cycle batteries which aren't designed to deliver huge currents quickly. And, don't forget voltage: the start battery should always be topped off, while the deep-cycle house batteries may be well depleted after several days at anchor.

To me, using thick-plate deep-cycle batteries for engine starting instead of properly designed thin-plate engine start batteries is like the guy who eschews the use of Phillips-head screwdrivers in the belief that if you choose the right size flat-blade screwdriver you can remove Phillips screws. Guess I'm just old-fashioned: I prefer to use the proper tool for the job at hand :-)

Bill
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Old 18-07-2011, 22:51   #9
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Re: Which Battery for the Bilge Pump ?

I have a large (almost...Just 4 golf cart batterys) house bank and a dedicated start battery fed with an echo charge.

One reason to use a start battery rather than a "reserve" battery is to test the ability of your starter/reserve battery to actually start the engine.

All pumps are wired to the house bank.

Regards, Ethan
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Old 27-07-2011, 13:16   #10
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Re: Which Battery for the Bilge Pump ?

If you want redundancy for your bilge pump you can always install a relatively heavy duty single pole double throw switch so that you can select a theater battery. My personal preference would be to have 1, 2, or both switches. One of them would be to select the house bank in the other would be to select up the starting bank. I would have both of the 1, 2, both switches with alternator protection circuits. Just my two cents, Mike.
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Old 27-07-2011, 14:18   #11
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Re: Which Battery for the Bilge Pump ?

Quote:
Originally Posted by btrayfors View Post
It's not the average draw of the starter that matters. It's the in-rush current, which typically is MUCH higher and can easily exceed 1,000 amps for about 1/4 second each time you press the start button.

I don't know what engine you have, but my 4-108 draws a heck of a lot more than 100A. When I first put an ANL fuse in line, I blew one with a rating of 250A! The 400A one I've been using for several years seems about right for my engine. One of these days I'll measure the in-rush current.

Meanwhile, it might be instructive to read what Blue Sea Systems says about engine starting in-rush and cranking current, and think about what you're asking heavy-plate deep-cycle batteries to do: Blue Sea Systems Engine Starting Standards - Resources - Blue Sea Systems

Yes, of course, deep cycle batteries are best for the house bank. I hope you didn't misunderstand me, since this is what I intended. But, little question about it, batteries designed for starting engines are "better" at the task than are deep-cycle batteries which aren't designed to deliver huge currents quickly. And, don't forget voltage: the start battery should always be topped off, while the deep-cycle house batteries may be well depleted after several days at anchor.

To me, using thick-plate deep-cycle batteries for engine starting instead of properly designed thin-plate engine start batteries is like the guy who eschews the use of Phillips-head screwdrivers in the belief that if you choose the right size flat-blade screwdriver you can remove Phillips screws. Guess I'm just old-fashioned: I prefer to use the proper tool for the job at hand :-)

Bill
I have to disagree with you on whether deep cycle batteries can't handle starting loads--I just checked the specs on a 100 amp gel battery and it is rated for 2600 amps for 5 seconds.
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Old 06-05-2017, 14:24   #12
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Re: Which Battery for the Bilge Pump ?

I have one disagreement with the wisdom posted above. As a marine technician I hate 1-2-b-n switches. The participants in this discussion surley know thier boats well, and understand what each switch actually does. However I find this rare. 95% of the time we go on a customers boat we find the battery switches set to "both". It really is epidemic. I prefer a dedicated on-off for each job. "Is the house on?" becomes a yes or no question. Same for the engine. An Emergency Paralell or "tie" switch labled as "emergency" keeps things clear. Combined cannot be mistaken as normal. If the tie is on the load side of the on-off switches then a failed battery can be isolated by operating the tie with one switch off. This would be an "Emergency Load Paralell System".
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Old 06-05-2017, 15:27   #13
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Re: Which Battery for the Bilge Pump ?

Quote:
Originally Posted by Flcapt View Post
I have one disagreement with the wisdom posted above. As a marine technician I hate 1-2-b-n switches. The participants in this discussion surley know thier boats well, and understand what each switch actually does. However I find this rare. 95% of the time we go on a customers boat we find the battery switches set to "both". It really is epidemic. I prefer a dedicated on-off for each job. "Is the house on?" becomes a yes or no question. Same for the engine. An Emergency Paralell or "tie" switch labled as "emergency" keeps things clear. Combined cannot be mistaken as normal. If the tie is on the load side of the on-off switches then a failed battery can be isolated by operating the tie with one switch off. This would be an "Emergency Load Paralell System".
Agree 100%. The 1-2-Both-Off switch is the root of many electrical problems.

Here's a better way, using inexpensive but robust Blue Sea Systems 6006 battery switches.

Click image for larger version

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As Flcapt said, this avoids a lot of misunderstanding and inadvertent damage to 12V system.

Bill
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Old 09-05-2017, 08:41   #14
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Re: Which Battery for the Bilge Pump ?

I have been using the 1-2-Both-off switch for so many years that my habits are pretty reliable. But, since I'm thinking of replacing my old Guest 2515 battery charger with a three phase, Blue Sea charger with built-in ACR, I would always select the starting battery for starting the engine, with the ACR diverting alternator current to the house bank once the starting battery had reached a full charge. Then, I would have to remember to switch to house bank when I turn the engine off. BUT WILL I REMEMBER?
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Old 09-05-2017, 10:32   #15
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Re: Which Battery for the Bilge Pump ?

Quote:
Originally Posted by Flcapt View Post
I have one disagreement with the wisdom posted above. As a marine technician I hate 1-2-b-n switches. The participants in this discussion surley know thier boats well, and understand what each switch actually does. However I find this rare. 95% of the time we go on a customers boat we find the battery switches set to "both". It really is epidemic. I prefer a dedicated on-off for each job. "Is the house on?" becomes a yes or no question. Same for the engine. An Emergency Paralell or "tie" switch labled as "emergency" keeps things clear. Combined cannot be mistaken as normal. If the tie is on the load side of the on-off switches then a failed battery can be isolated by operating the tie with one switch off. This would be an "Emergency Load Paralell System".
I also agree with the above. I (will when I get them in) have a separate parallel switch for the rare times I want to use the house bank for an emergency start when the start battery is dead. Because I have a genset I will use a 1-2-B or 1-2-A switch to start either motor with the start battery.

Also, and some will disagree with this, I have two circuit breakers on my new DC panel - one for Auto Bilge Pump and one for Manual Bilge Pump, with a red panel light I added to show when the pump is running. There are little BP panels you can get to do the same thing, some with C/B's and some with fuses. My C/B's are not powered by the panel's main DC switch but go direct to the house battery. I wanted an easy to get to switch in case I need to stop the bilge pump (runaway or problem with the BP water level switch). Both C/Bs have toggle guards to prevent accidental changes. The Auto one will always be on.
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