Re: 1976 22' Starcraft Islander Rebuild
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Complete and total change in direction real quick. I was yacking it up with an iboat buddy off the forum regarding electrical stuff. So....
On my rigs there was a certain point where I was sold on the ACR. Well, until I found a few posts like this by silvertip (I wanted to be sure to give him credit):
So yah, I'm buying what he's selling. I just wanted to drop that in here so you guys know why I didn't go with the ACR anyway. That's just me though eh:joyous:
I know Silvertip is a very wise and all knowing guru, and his 1/2 both switch is very simple, and does exactly what he says, but he misses some important pro's for running ACR or VSR. On my boats, I want a starting battery only to do just that, start the boat, and not have other electronics sucking power from it... I want everything (all electrical) on a deep cycle house bank... And I don't want to worry or remember when to switch one or two, or both.... I prefer dedicated battery systems, and use a VSR/ACR to isolate and charge them. If my dedicated start battery died, I can still use my house bank to start my boat... The ACR also can help protect/isolate circuits from transient voltage caused when cranking your engine occurs. The fuses that protect the GPS, and other expensive goodies can possibly fry... But then you need to deal with that... Below is a good read on why ACR's have some advantage over simple switch only systems. If you still decide not to use a VSR I totally understand, but at least get dual-purpose group 31 batteries so as not to use a cranking battery for house electronics, especially a trolling motor.
Love Bear
The ACR is typically wired so that an auxiliary battery is placed in parallel with the main battery (by the switch closure) when the sense voltage is above threshold, that is, whenever there is charging current available and the main battery voltage has reached full charge.
This simple circuit has been enhanced in several ways. The most common is to include a hysteresis in the sensing circuit so that the ON voltage threshold is higher than the OFF voltage threshold. This helps to prevent the circuit from chattering on and off. Without a separate threshold, there could be situations where the addition of the second battery to the charging circuit would immediately drop the voltage below threshold. This would, in turn, immediately cause the relay to drop out. And this would then raise the voltage. The cycle would repeat. Having some hysteresis in the control loop helps to reduce this tendency.
One of the principal advantages of using an ACR or VSR is to help isolate the electrical circuits in the boat into two distinct groups:
--battery and loads associated with engine starting
--battery for all other loads
The engine starting loads are typically just the engine, its solenoid, and its starting motor. The other loads are vessel lighting and electronics.
The reason for maintaining isolation is twofold. On engine start there are often voltage transients produced. These voltage transients can cause interference with or damage to electronic devices. Isolating the starting loads from the electronic loads will prevent starting transients from reaching the electronics. The other advantage is isolation of the starting battery from discharge by any load except the engine. This will prevent the starting battery from being drained by non-starting loads (such as lights, pumps, or electronics) when the engine is not running. Larger horsepower engines are very difficult to pull start, so it is paramount that the engine starting battery be kept fully charged and able to crank over the engine for starting.
The general design of an ACR or VSR has been intended to only connect the two battery systems when the engine is running, that is, when the engine is putting out charging current and the engine starting battery has reached a full-charge terminal voltage. In most cases this will occur only when the engine is running. However, it is possible that if both batteries are near full-charge, an ACR or VSR could be fooled by the high resting voltage of the two batteries, and the voltage on the sense line may be high enough to trigger the switch to the ON condition. This will parallel the two batteries, even though the engine is not running.
The harm in this comes when the engine is cranked over for starting. If the ACR or VSR has paralleled the two batteries, voltage transients from starting may reach the electronic loads. If this occurs, one of the main reasons for using an ACR or VST is lost: the electronic loads will not be isolated from starting transients.
To overcome this situation, Blue Sea Electronics have developed a more sophisticated version of the ACR. They call their device a starting-isolated ACR. The ACR switch is always opened during starting. This is implemented with a simple circuit which monitors the engine starter solenoid line. When the engine is cranked, voltage on the engine solenoid line is sensed and the ACR switch is immediately opened (if closed). Blue Sea says that the switch operates fast enough that it is open before any transient voltages develop during cranking.
