battery question

[nightvision]

Hi all,<br />I just got a minn kota trolling motor (Endura 50). The manufaturer recommend a deep cycle Marine 12 volt battery with atleast 105 ampere hour rating. I do have a deep cycle battery from my tent trailer and I like to use it for this trolling motor when we are not camping. I look at the battery but can not tell if it has 105 ampere hour rating. Here is the info I can see on the the tent trailer battery.<br /><br />Trojan Outdoor, Duel purpose starting/deep cycle 24TM<br /><br />Specs:<br />85 AH at 20 Hr.<br />66 AH at 5 Hr.<br />135 min at 25 amps<br />550 cca at O degree F<br />675 cca at 32 degree F<br />12 volt battery<br /><br />Would this battery be appropriate for the trolling motor? Thanks.

 

[trog100]

Re: battery question

its bit small.. <br /><br />85 AH at 20 hr means it will deliver a 4 amp load (85 AH at 20 Hr) for roughly 20 hours.. <br /><br />or a bigger 15 amp load (66 AH at 5 Hr) for about 5 hours..<br /><br />or a 25 amps load (135 min at 25 amps) for 2 hour 15 minutes..<br /><br />it would be called an 85 amp/hour battery in simple terms.. but as u can see it aint that simple.. the more load u put on a battery the less its capacity..<br /><br />all this is with a brand new battery.. fully charged and being fully flattened.. u really dont want to take em any lower than say about 30% flat else they dont live very long..<br /><br />soooo.. work out what current your motor draws.. work out how long u want it to run for between charges.. allow 2/3 the rated capacity of the battery.. (call your 105 AH battery a 66 AH battery for example) then u know what size battery u need.. <br /><br />an example.. lets say a motor draws 20 amps.. a 100 AH battery would run this from fully charged to 30% flat/charged for about three hours.. your spare 30% could be used in an emergency for about another hour but shouldnt be done on a regular basis as its not good for the battery to fully flatten it..<br /><br />all these figures are rough examples and in reality would probably be worse cos a battery dont stay brand new for long and it aint always fully charged to start with..<br /><br />what size battery u need depends on how long u wish to power the motor for and the current the motor draws.. as a general rule the bigger the battery the better.. the longer it will power the motor for and the longer it will live before needing replacing..<br /><br />there really is no ideal battery size.. it all depends on your motor current draw and how long u want the battery to provide that current for..<br /><br />u can bet the manufacturer recommended battery is on the mininmal size thow.. it aint good for sales to suggest u need a bigger one..<br /><br />sorry about it being complicated.. but i couldnt explain it any differently..<br /><br />and if anyone accuses me of being long winded (as as happened before) well they know what they can do.. he he<br /><br />trog100

 

[nightvision]

Re: battery question

Like Oz said, the slower the discharge, the more amps a battery will cough up. The std spec for a/hr is based on a 5% rate of discharge, or 20-hrs of discharge (20hrs x 5% = 100% discharge). At 5% you get a reasonable amount of energy for the greatest length of time.<br /><br />There is a curve for other rates of discharge. This becomes important when using limited battery resource for high-amp demands, like trolling motors and house banks. Manf of quality bats, like your Trojan, publish the discharge curves for their bats.<br /><br />Aldo is correct, there are more specs for a battery than you can shake a stick at. They go on for pages and pages and pages. A couple of my personal favs are ‘float life’ - how long before a bat dies if left on a float charge, and ‘short circuit potential’ - how many amps would a bat cough up if it had theoretical unlimited capacity and you dropped a wrench across the posts.<br /><br />Nightvision – you said the manf recommended a 105a/hr battery. We talk about a battery’s capacity based on that 20-hr discharge rate. Common group-31, and group-27 bats are around 105a/hrs. Your Trojan (excellent battery, btw) is 85a/hrs…that’s about right for a group-24 battery, and some gel group-27.<br /><br />Group numbers are a std for the physical ‘fit’ size (H x W x D) of a battery and have no reference to a bat’s capacity, tho bigger obviously should imply more capacity. So all group-24 batteries will ‘fit’ in the same space, all group-27 bats will fit in the same space, etc. Based on what the manf says, you want a minimum of a group-27 battery, a group-31 would be better if it will fit on your boat.<br /><br />The last pair of specs in your post refers to the batteries ability to cough up very high-amps at a couple diff temps. They are commonly referred to as CCA (cold cranking amps), what a bat can deliver for vehicle starting applications at 0-deg F, and MCA (marine cranking amps) for starting boats at or above 32-deg F. MCA is done at 32-deg F because you get a bigger amp punch when a bat is warmer than 0-deg, and since boats aren’t going anywhere in frozen water (think: ice below 32-deg F). The CCA spec is of little value for boats, except maybe to compare bats.<br /><br />Someone else can weigh in what the benefits of recharging your bat asap after trolling.

 

[nightvision]

Re: battery question

Hi all,<br />I looked up the specs for my trolling motor and it said Max AMP Draw is 42. Will my group 24 be able to to handle this motor and about how long will it last. If I nee a new one, do you recommend a group 27 or 30?

 

[CATransplant]

Re: battery question

It'll run your motor at full speed for about 1 hour. No more than that. You're probably going to want a bigger battery for that larger trolling motor. Of course, bigger batteries are heavier, so a lot depends on what your boat can handle.<br /><br />One thing a lot of guys do, instead of having one huge battery is to have a couple of smaller ones running either in parallel or used sequentially (one starts slowing down...switch to the other). There's some sense in that, since you can position two (or more) batteries to balance the load.<br /><br />The other thing you'll want to do is invest in a smart battery charger. They're ideal for deep cycle batteries, since they require little attention. If you mount the batteries semi-permanently in your boat...get a charger that mounts in the boat...saves time.