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Old 10-10-2012, 08:51 PM   #21
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Andy,5 years from batteries is good and suggests good management.
There are 2 features of the early 1980s IG twin engine battery set up:
1. It has 2 200 amp hour batteries,one for each engine. they do both starting, and house supply.There is no dedicated house battery.
2. The batteries automatically parallel when you hit start.
The Owners Manual p9 says " The battery selector switch ....connects either or both batteries to the service system. Except in the case of charging both batteries by the same engine alternator the selector switch should not be used in the all position"
That seems to suggest using one or both for house,but it seems odd you should set to 1 or 2 when operating both engines.I also admit using the "both" position when running,with no obvious ill effect.Any ideas out there about this?
Because of the dual demands on batteries,I use Century Pro Cruiser N200M flooded batteries which are marketed as dual purpose.
If when anchored, you use 1 or 2 but not both, you risk overdrawing the one you use, whereas if you use both the draw is spread and neither may be overdrawn, but you risk overdrawing both if not careful. You could try alternating between 1 and 2 overnight, keeping the other as a fully charged start battery, effectively creating a de facto dedicated house and start set up, and see how it works by checking the voltmeter.
For a time I had one new and one "ok" but not new battery. Performance improved markedly when I renewed the "ok" one. Otherwise the better one drains to the worse one,and because the worse one can`t hold charge well, the draining never ends.
To maintain the batteries,mine are each fed by 90w of panels via regulators which include a monthly "equalization" phase to shake any sulphation off the plates back into solution.
Back up remains the genset. Mine has a regulated 25w panel for its 150 a/h battery. While running the eutectic refrigeration an hour morning and evening using the genset,I also charge batteries,and of course run the espresso coffee machine. BruceK
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Old 10-10-2012, 09:20 PM   #22
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Greetings,
OK, you've got 2 batteries (or banks). The house battery is depleted to 9V- (and isolated via switches or what-ever) due to over-use of your disco ball and repeated showings of Saturday Night Fever. Not a hope of EVER starting your main(s) with that lot. You introduce your starting battery into the circuit (floating @ 14V+/- fully charged) to start main(s). What you are saying is: since being parallel with your depleted battery you will not have enough juice to start due to "fresh" battery draining to dead battery? Hogwash, in the short term. Yes, over time the two batteries will equalize to a state where there is not enough power to start your main(s) but you SHOULD be able to get going with the immediate added voltage.
As to keeping at least a minimum of battery(s) isolated and dedicated for main(s) start-up, I agree.
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Old 10-10-2012, 09:53 PM   #23
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RTF, I think you are misreading my post. I am equally confident the fresh unused battery would start the engine,that`s why I talked about creating a de facto start and house system by selecting only one battery and preserving the other while on the hook. I agree draining from the "good" to the "bad' battery would take time. The IG system would parallel the batteries the instant you hit the starter, before any draining could occur. BruceK
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Old 10-10-2012, 10:05 PM   #24
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Greetings,
Apologies for misinterpretation.
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Old 10-10-2012, 11:45 PM   #25
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Phew, I thought I had wandered into ODT for a minute.

Thanks all for your views and advice. For the record I have a similar system to Bruce's IG. I would love a separate starting battery, simply no room in the engine bay, or up forward. I also use my 7KVA gen each morning and evening to recharge etc. when on the hook, so the present system does work, although it is not optimum.

One issue though, with the new batteries, my electrician suggested I put in Federal 908DFT's, flooded batteries.These were the largest batteries that would fit into the existing battery box's & one of the reasons for this choice being they are sealed, ie don't need topping up, which seemed a good idea to me, so went ahead and had them installed. I rang the Federal distributor here in Oz to have a chat and was told these batteries are not sealed and they would require topping up time to time.The invoice clearly states they are 'maintenance free', so I guess I'll need find out for sure, who is right. Want to keep these batteries for another five years if possible.
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Old 10-11-2012, 12:03 AM   #26
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Phew, I thought I had wandered into ODT for a minute.

Thanks all for your views and advice. For the record I have a similar system to Bruce's IG. I would love a separate starting battery, simply no room in the engine bay, or up forward. I also use my 7KVA gen each morning and evening to recharge etc. when on the hook, so the present system does work, although it is not optimum.

One issue though, with the new batteries, my electrician suggested I put in Federal 908DFT's, flooded batteries.These were the largest batteries that would fit into the existing battery box's & one of the reasons for this choice being they are sealed, ie don't need topping up, which seemed a good idea to me, so went ahead and had them installed. I rang the Federal distributor here in Oz to have a chat and was told these batteries are not sealed and they would require topping up time to time.The invoice clearly states they are 'maintenance free', so I guess I'll need find out for sure, who is right. Want to keep these batteries for another five years if possible.
My Century branded (?Yuasa made) 200 a/h batteries are described as "low maintenance". Maybe for Federal, no= low. You may be better off able to top up. Mine need top up after using the 12v fridge when the batteries are active as the solar panels get to work, but most of all after the monthly equalization. Yours may need less attention. Be sure to get help lifting them in. BruceK
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Old 10-11-2012, 08:21 AM   #27
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RTF, I think you are misreading my post. I am equally confident the fresh unused battery would start the engine,that`s why I talked about creating a de facto start and house system by selecting only one battery and preserving the other while on the hook. I agree draining from the "good" to the "bad' battery would take time. The IG system would parallel the batteries the instant you hit the starter, before any draining could occur. BruceK
The depleted battery will not help start the engine and the non depleted battery will have the extra load of the depleted one. It doesn't matter that it takes a while for them to reach an equal state of charge.

Think of the difference between starting your car with the headlights off and with the headlights on.
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Old 10-11-2012, 08:28 AM   #28
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Phew, I thought I had wandered into ODT for a minute.

Thanks all for your views and advice. For the record I have a similar system to Bruce's IG. I would love a separate starting battery, simply no room in the engine bay, or up forward. I also use my 7KVA gen each morning and evening to recharge etc. when on the hook, so the present system does work, although it is not optimum.

One issue though, with the new batteries, my electrician suggested I put in Federal 908DFT's, flooded batteries.These were the largest batteries that would fit into the existing battery box's & one of the reasons for this choice being they are sealed, ie don't need topping up, which seemed a good idea to me, so went ahead and had them installed. I rang the Federal distributor here in Oz to have a chat and was told these batteries are not sealed and they would require topping up time to time.The invoice clearly states they are 'maintenance free', so I guess I'll need find out for sure, who is right. Want to keep these batteries for another five years if possible.
No such thing as a seal flooded battery. GEL and AMG yes flooded no. They need to breath due to the manufacturing of H. So there needs to be a way to add water. These batteries may have a better recapture system than regular batteries but they still will lose H2O to the atmosphere.
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Old 10-11-2012, 08:57 AM   #29
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No such thing as a seal flooded battery. GEL and AMG yes flooded no. They need to breath due to the manufacturing of H. So there needs to be a way to add water. These batteries may have a better recapture system than regular batteries but they still will lose H2O to the atmosphere.
There are many "maintenance free" flooded batteries. Many cars and trucks come with them. "Maintenance Prevented" might be a better term but they are out there.

http://www.theautochannel.com/news/2...30/150966.html

BTW: That would be "AGM", not "AMG".
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Old 10-11-2012, 09:14 AM   #30
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If you're trying to start you engine, the fully charged battery is splitting its power between the starter and the discharged battery.
Not really, the internal resistance of the discharged battery is higher so more power flows from the charged battery to the starter. Very very little is used to charge the discharged battery as starter current flows.
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Old 10-11-2012, 10:08 AM   #31
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BTW: That would be "AGM", not "AMG".
JD *DOES* drive a Mercedes, so we should excuse the Freudian slip.
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Old 10-11-2012, 10:19 AM   #32
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Major difference of opinion here so who is right Rick or Ron.

Does the low battery discharge the charged batterie.

Or does the two combined act as a more charged battery.???

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Old 10-11-2012, 10:35 AM   #33
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Or does the two combined act as a more charged battery.???
That was not the statement. Look at how current flows through parallel resistance in a circuit.

But, there is more power available in pair of batteries if one is half charged and the other fully charged than if one is "dead" and the other fully charged.
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Old 10-11-2012, 10:41 AM   #34
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As I understood Rwidman. When two batteries are combined the less charged battery will draw down the charged battery.

I thought the implication was this happens instantaneously. Therefore combining batteries is pointless. Am I right or wrong.

Rick. What if both batteries are partially charged?

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Old 10-11-2012, 10:46 AM   #35
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Combining batteries is not pointless. If it were we would not have a group of cells combined to form a battery.

If both batteries are partially charged then you have less power available than if they were both fully charged, that's all.
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Old 10-11-2012, 11:00 AM   #36
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If the batteries were in series it would be different.

Say you need 12v to the starter and had two 6v batteries in series. If one were low (or dead) the low battery would adversely affect the other when trying to use because the voltage of the combine would be lower than optimum and the starter would turn too slowly to start.

This isn't the case in a parallel circuit. While the voltage is the same (assuming they are all generally the same voltage to start), the amperage supply is deeper, and thus will provide increase current to the load. Yes, the voltage would be lower, but only to the average of the two voltages and not the sum. (Did I say that right? Been a long time since college.)

If I understand it correctly, the big deal with mixing dead batteries and good ones (or having a dead-ish one among your cluster) is during the state of charging.
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Old 10-11-2012, 11:13 AM   #37
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Now I am totally confused.

If you have two 12 volt batteries. One is say 11.5 volts the other is at 10 volts.

If you combine the two what do you get?

I know you will not get more than 12 volts. But will it give you any extra juice to start your engine?

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Old 10-11-2012, 11:30 AM   #38
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Boy, you're testing the old brain cells today... It depends on the internal resistance of the lower voltage battery, but generally it will be closer to 11v. What is happening is the current from the higher source is driving into the lower one. Joining two batteries of different voltages would cause a current to flow between the batteries as follows.. I = (Vbatt2 - Vbatt1) / (Rbatt1+Rbatt2)
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Old 10-11-2012, 11:54 AM   #39
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Now I am totally confused.

If you have two 12 volt batteries. One is say 11.5 volts the other is at 10 volts.

If you combine the two what do you get?

I know you will not get more than 12 volts. But will it give you any extra juice to start your engine?

Sd
I think of it this way: Voltage differential is synonymous with the size of a water pipe. Current is the water flowing through the pipe. Undersized cabling is like having ridges inside the pipe causing increased resistance to the flow of the water. If the voltage is high (big pipe) and the cables are adequately sized (smooth inner walls of the pipe), then the current flows with less resistance. That's why our alternators put out 14V (+/-) for a 12V system, so current will flow from the higher voltage alternator to the lower voltage battery.

If you have batts with 11.5V and 10V, you've really got 2 low batts. A fully charged battery in a steady state should read 12.6V. The 10V batt may have a bad cell or 2 cells shorted out causing the low voltage. Optimally, each cell should provide 2.1V. If one is dead, you'll get 10.5V at best. But let's look at the situation with these numbers.

If you put a voltmeter on each batts when separated, you'd see 11.5 and 10V. The instant you combine them, you'd start to see the 11.5 gradually decrease and the 10V may or may not slowly increase, depending on it's condition. The 11.5V decreases because the 10V batt places a load on it and the current flows from high voltage to low voltage.

If the 10V batt is your start batt, it's too low to start the engine. By placing the switch to "ALL", you allow the better 11.5V batt to assist in the process. But it must still flow "through" the high resistance of the 10V battery to get to the starter. It would do a better job of starting if the 11.5 could provide the start power without the 10V batt in the circuit, but few if any of us have redundant cabling to allow is to completely bypass the bad batt without recabling or use of jumper cables.
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Old 10-11-2012, 11:57 AM   #40
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There are many "maintenance free" flooded batteries. Many cars and trucks come with them. "Maintenance Prevented" might be a better term but they are out there.

Car Battery Maintenance: To Water or Not to Water?

BTW: That would be "AGM", not "AMG".
Wow what a bunch of legal speak. Who wrote that Congress? " "But in a properly designed, voltage-regulated system, water loss should not cause maintenance-free batteries to fail," said Mr. Hart." Unfortunately this is not the case in most boats. You can't stick them in there and forget them. Had a friend at the last marina who was going crazy because when he took the boat away from the dock nothing worked. I asked if he had checked the water in the batteries and he said he didn't have too because they were "maintenance free". I checked they were dry and he replaced them and all was well.

One more thing. When the battery dies in a car or truck you pick up your phone and call. Someone will come get you and within an hour or so you are on your way. Boat, not so much.

Thanks about the AGM and AMG. I know but I'm a little slow some days. The front spoiler on my MB is low enough I don't need the air dams the AMG's have.
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