Charging a deep cycle battery

[scater]

I have a deep cycle battery which runs my electric motor. I've ordered a good 7-stage charger for it but in the mean time, can I top it up with the 12-volt charger I use for my sounder battery? If so, is there a maximum amount of time I should have it charging for? It's a 75ah battery and the indicator on the minn Kota says it's half full.

[Yippy]

How long does your battery last in a normal days fishing? The Min K manual says that my motor draws 1amp per hour for each pound of thrust produced with motor running at high. At this rate, a motor would drain a 75ah pretty quickly if you are to only use 50% of your capacity.
Appreciate your advice to help with me working out what size battery I should buy?

[dru]

To be honest I dont have an answer, but deep cycle batteries need to be run dead. They don't like constant top up on trickle charge. So I'm guessing, try to flatten it down to 10% or 15% first, then charge up to 100% but don't leave it charging after.

We've been working through design for power renewables in building. They have memory if you don't treat them right, but of course it's a completely different application. We will drop charge down to 30%, but there are technical reasons for this (we need some oomph for spike loads at min charge), and we will make sure the control system doesn't keep them charging once full.

[scater]

That's the exact opposite of what I've been told Dru, in fact I leave the charger on permanently on the float charge. I'm using a Projecta Intellicharge 7-stage charger and was under the impression that this was the correct procedure.

As for Yippy's question, I'm not sure yet about how much power the motor uses. I don't use it like a yakker would (it's a bow mount on my boat). It doesn't get used for trolling or moving the boat more that about 50m. By far the majority of it's use is in maintaining position during a drift so short bursts are all that's needed. In this function I've never been below 50% as indicated by the little dial on the motor even after 2 days of solid fishing. It should be noted however that the battery also charges from the alternator on the 4-stroke.

[Lazybugger]

Scater I'd head over to exploroz.com.au and do a search. Its the AKFF of Aussie camping sites with plenty of knowledge to be gleaned. 12 volt power is always a hot topic for fridges, so the knowledge you need should be transferable to your motor. Of course talking batteries will raise a range of views on whats best. From memory the concensus is not to drain them fully and thats why a good float charger is recommended for all Deep Cycle and Gel batteries if they aren't going to be used for long periods.

[dru]

There we go, wonder why the different advice on different applications.