Posts: 2752
Location: Mauston, Wisconsin | Guest - 12/22/2008 3:51 PM
you really don't want to mix batteries for a variety of reasons. consider using the trojan for your other stuff and get two new ones, they really will last alot longer.
It's amazing that these lead-acid battery "urban legends" still exist. Just go buy another Trojan of the same size. Adding a new battery in series with an older battery to supply 24V to your new TM isn't going to affect the useful life of either battery. In fact they don't have to be the same size nor do they have to be the same manufacturer or even the same lead-acid type (wet-AGM-gell). No matter what, make sure you charge them separately, i.e., with stand-alone 12V charger or an onboard dual battery/split bank charger. Don't buy a 24V only charger.
For cable sizing follow your trolling motor manual installation recommendations. Beware of using to small of a cable (don't go small to save money). If your TM data plate instructions call for 50A wire - you need #8 AWG minimum. If you're running the cables 15-20' you might want to consider #6 AWG. F.ex With a 50A load the #8 AWG 20' circuit voltage drop will be ~ 1.6V - Thats ~81watts of power being lost in the cables. If you use #6AWG the voltage drop will be ~ 1.02V and power loss in the cables would be ~51W. If you want to squeeze maximum performance from your battery and the TM consider larger cables. In no circumstance should you use anything smaller than what the manufacturer recommends, including a inline fuse or circuit breaker to protect the cables and the TM.
#6 AWG = 65A max
#8 AWG = 50A max
#10 AWG = 35A max
#12 AWG = 25A max
The above are with a 75C (167F)cable temperature in a 30C (86F) ambient, this is the effect of watt loss/heat in the cables.
Good luck.
Al
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