Saturday, Jan 17, 2004 at 02:47
Dozer, yeah you need to use a surge protected jumper, I agree.
But the flat aux to full main, there is a surge form the main to the aux when it connects. The alternator can supply say 90 amps on initial connection plus whatever from the main battery. As you say, there is that initial surge, but the wiring should be rated to at least what the alternator can supply. Thus there is now say 180 amps available to charge the flat aux.
But there is no way you can pump that sort of amps into a lead acid battery hence the main battery will not actually supply anywhere near 90 amps, the batteries internal resistance is way too high.
If one is conncerned about this "reverse" flow, then you can easily install another connection from the main battery to the solenoid in addition to the one from the alternator. But IMHO this is not necessary.
The advantage of direct connection from the alternator to the solenoid is the ability to actual use the full output of the alternator. While the factory wiring may handle 90 amps, there is a voltage drop due to the smaller size wire compared to the new wire installed to the isolator (note - one defeats the purpose if only a small guage wire is used form the alternator to the solenoid). Even a small voltage drop makes a notable difference to battery recharge rates.
As for alternator sensing, when both batteries are commoned and the aux battery is relatively flat, the charge equalisation (as both are connected they must be at the same voltage) lets the alternator charge at a higher rate. But there is a significant difference in amps sent to each battery due to the different internal resistance of each battery.
But the point you raised about the rush of volts is valid if a gel cell type battery is used. They have very low internal resistance and this is why they can recharge so quick (high input amps).
Ideally, the rotronics type of isolator is superior as it directly connects the alternator to a single battery at a time. This stops the charge equalistion and allows maximum battery recharge. However, the cost of the complete kit is IMHO too much for its advantges.
Cheers
Mark
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