Do I need two batteries?

[tengals123]

I will be running a colour sounder, a cd player, a radio, nav. lights, gauges, bilge, two small deck light. Of course not all at once.<br />Currently I have 1 (500???) marine grade battery, do I need more or two batteries. I'd like to be able to keep cd and radio and finder on most of the time.<br /><br />cheers

 

[Silvertip]

Re: Do I need two batteries?

For reliability I would recommend two: one large deep cycle to run all accessories and the starting battery for starting, bilge pump, and possibly marine radio & lights. That way you don't have to worry about a flat starting battery when its time to head home.

 

[Perfidiajoe]

Re: Do I need two batteries?

I would put in 2 batteries, & a switch. It sounds like a lot of draw on one battery, especially if you add running lights, a VHF radio, & maybe a G.P.S. There are a few different schools of thought on what to wire to which battery, & a lot depends on if you leave the boat in the water or not. If you fish you may want to have your GPS, & sounder on & unaffected when you start the engine, as not to lose the settings every start. Some people w/ 2 batteries have 1 for starting, & 1 deep cycle for running the electronics, get the proper switch, & consider your charging output. Good luck, Joe

 

[tengals123]

Re: Do I need two batteries?

ok, so what sizes etc. Dunaruna, if your there, in australia, what should I be looking for. I already have a century marine 500, what other batt. should I get? and switch reccommendation?<br /><br />cheers

 

[Dunaruna]

Re: Do I need two batteries?

For deep cycle - I like the mercury (not the outboard but the battery brand) N70ZZ, expect to pay around $120.00 (give me a call if you can't find one for that price) but you gotta keep it seperate from the starting battery by using a isolator, my preference is a VSR (voltage sensing relay). Far left on that pic of mine (the voltage vault). Century is also a very good brand and they make a N70ZZ but it's more expensive I think. <br /><br />Aldo

 

[Dunaruna]

Re: Do I need two batteries?

Forgot to add, <br /><br />I don't like the rotory type battery switches, manual switching has it's uses but a VSR does it all automatically, it will keep the batts seperate and charge each automatically - a good VSR is also a pulse charger, VERY good for deepcycle batteries. If you get a rotary type master switch make sure you get one that maintains continuity when switching.<br /><br />Aldo

 

[tengals123]

Re: Do I need two batteries?

so i could get a N70ZZ and connect it to a rotary switch, then keep my existing batt. and connect to the switch also. Leave the switch on 'both' and away we go????<br />is that right?<br /><br />cheers

 

[amirm]

Re: Do I need two batteries?

At the risk of asking an obvious question, are you running the engine with this gear on? If the engine is running, a single battery would be just fine. If you are not, then your average current usage would be around 8 to 10 amps. Decide how many hours you need to run this, then multiply by two and you get the battery capacity needed in AmpHours. For example, if you want to run this gear for 5 hours, you would need 5x8x2 = 80 amphours. Any battery larger than this would do.<br /><br />Amir

 

[Dunaruna]

Re: Do I need two batteries?

That'll work but if you leave the switch on 'both' the batteries will equalise, they will be connected. For safety reasons it is far better to keep them isolated then you are ensured that at least one battery has enough juice to start the motor. If one battery becomes weak you won't know until both are close to dead, the weaker of the two will kill the good one and you will have no 'good' battery for starting. In addition, coupling a deep cycle (often much bigger than a starting battery) and a standard starting battery together will kill both batteries much quicker than normal, they require different charging cycles and times. A VSR 'knows' this. You can use a rotary switch to properly charge both batteries but it would require manually switching from '1' to '2' at certain times by using two seperate volt meters as a guide. It is far simpler to isolate. <br /><br /><br />Aldo

 

[tengals123]

Re: Do I need two batteries?

ok, now im getting it. my centruy 500, don't know if that's quite large or not? Wouldnt it be ok if I just bought another 500 marine and parralled the two. And kept an eye on the volt meter? I fish for about 8 hours everytime I go out?<br />also dunaruna, if I bought a VSR, how much would it cost? BTW supercheap doesnt sell those circuit breakers we were talking about. Is there some where I can go to get one of these VSR's and circut breakers at the same place for a cheap price. I just don't want to speand an arm and a leg for electrical. I really don't use much stuff.<br /><br />cheers<br />cheers

 

[Dunaruna]

Re: Do I need two batteries?

I think a BEP VSR is about $150. Only available through a marine supplier such as whitworths. BEP is the brand name. The CB is narva, very common brand in Australia, I'm surprised supercheap don't have them. Repco & burson certainly do. <br /><br />Paralleling 2 same size batteries will work, It's just not ideal - but it will work. Just remmember that the available AH will only be as good as the weakest battery, the weakest will be the oldest. It is generally accepted that when replacing a weak battery in a two battery system that you replace both so that they die slowly together, rather than one killing the other. Isolating avoids the need for same age same size batts.<br /><br />If your motor is easily pull started then my argument for a VSR is in vain - I'm just trying to save you future headaches. <br /><br />I'm a big believer in overkill, I needed 4 batteries to run my inverter - so I fitted six, I needed a minimum of 10 ah solar charging - so I got 2 x 9 amp panels. But that's just me, I like to have reserve.<br /><br />2 x century 500 is ample for your needs. <br /><br />Aldo<br /><br />Edit: We have 'talked' for a few months now, it's time you called me Aldo

 

[tengals123]

Re: Do I need two batteries?

Aldo, your knowlage is priceless. I know just about everything else there is to know about boats, but electric is my weakest point. Always learning, never stop learning. Thanks for all your help. I'm going to parrallel 2 marine 400 or 500's into a circut breaker then into a simple cutoff switch. When parrelling the batts. it's just + to + and - to - isn't it, using those thick terminal cables and lugs, is that right? I will then run all my wires up to the buses under the dash and other electronics off the 1 battery to make it neat and tidy. Does this sound right? also my Volts gauge should still read fine as it's still a 12v system. hope i've got this right?<br /><br />cheers<br /><br />cheers

 

[Dunaruna]

Re: Do I need two batteries?

Yep, + to + and - to -. Still give you 12 volts but double AH. When parallelling it is in effect making one battery out of two as long as the joining cabling is heavy enough. <br /><br />Aldo

 

[tengals123]

Re: Do I need two batteries?

done. thanks heaps mate. <br /><br />cheers

 

[Boatist]

Re: Do I need two batteries?

tengalsl23<br /><br />I not a fan of Parallel batteries. First off if you go parallel then both batteries should be same size and age and type. The best battery will be no better than the weaskest battery, meaning if you have a dead cell in one battery it will discharge the good battery. Far better to isolate your batteries with a battery isolator or a battery combiner.<br /><br />For the gear you have if you run your motor at all one battery should be fine. Two batteries does have added back up so should something happen to discharge your battery you can always start on the other battery. Of course if you wire them in parallel then they will both be dead.

 

[tengals123]

Re: Do I need two batteries?

urrrggggg. NOW, im really confused???<br />Honestly i'd love not to carry 2 batteries. But can I do it. I want to be able to sit and listen to music with my sounder on and cb on for 8 hours then come home and do the same thing the following week.<br />What to do now??<br />cheers

 

[Dunaruna]

Re: Do I need two batteries?

I'll try and clear it up for you.<br /><br />A normal marine battery will do the job but you would have no 'extra' for power hungry additions such as a CD player or maybe a spotlight.<br /><br />If you want extra juice you will need to add a second battery. <br /><br />There are basically three types of batteries on the market today.<br /><br />1. Shallow cycle - everyday run of the mill car battery, good for quick bursts of juice but they don't last very long if continually discharged and recharged, the discharge/recharge is what the 'cycle' in shallow cycle means. Take a bit off the top, put a bit back again - shallow cycle.<br /><br />2. Deep cycle - Built heavier duty, thicker plates, different medium composition. They cope much better with being discharged down to about 50% and then recharged, they can handle multiply drains and still recover. The're not indistructable but they will last longer than a shallow cycle. In fact a few car manufacturers are recommending deepcycle batteries due to the power hungry electronics of todays cars. There are different type of deepcycles on the market, rule of thumb is the more you pay the better the batt - and there are glaring differences, some cheaper deepcycles are good for anchors only.<br /><br />3. Dual purpose (both deep and shallow), they have'nt been around long enough for me to comment but initial reports are that they may be o/k.<br /><br />Many ways to add a second battery.<br />Listed from best way to the worsed way.<br /><br />1. Totally isolated charging circuit, this can be done with relays, a dedicated isolator or a VSR. A dedicated isolator tipically has a voltage drop of up to 1.5v - not a good idea considering the size of the mercs alternator, a VSR is far and away the best isolator.<br /><br />2. Keep the batteries completely seperate and charge up the second battery when you get home.<br /><br />3. Using a isolating soleniod that disconnects the batts when the ignition is off and joins them up when ignition is on, some soleniods have a 'jumper' switch that connects the batts is case of a failure.<br /><br />4. Do what you are talking about doing (sorry ) <br /><br />So, what to do? IMO if you can't afford the fancy electronics, don't fit a second battery. A cheaper option for now would be to replace your battery with a bigger one and add a small solar charger then sometime down the track add the second deep cycle with the VSR or do nothing for now. IMO.<br /><br />Aldo

 

[tengals123]

Re: Do I need two batteries?

Now, that is a great post. Thankyou for all the information. I shall report back shortly after I check out some prices.<br /><br />Thanks heaps Aldo.<br /><br />cheers

 

[amirm]

Re: Do I need two batteries?

Aldo's post is indeed superb. I would just add one clarification if I may. Option #1 is great if you have big enough alternator, and enough run time to actually charge the second battery. Let's me give an example. You say you use the electornics for 8 hours with the engine off. Assuming my rough current consumption of 8 amps, this means you will have depleted the battery by 64 amp hours. If your alternator puts out 20 amps, you would need three+ hours to fully charge your battery. If you trip home is only one hour, you wind up under charging the battery and after a while it will die.<br /><br /><br />So you may have to combine option #1 with #2. But before spending too much time thinkng about this, I would measure the total current consumption. It is really simple to do with a typical voltmeter that has at least 10 amp measurement capacity (not all do). Put that in series with your power source with everything else turned off other than the things you want to have running in this scenario and see what you get. If you can't find a convenient place to put the meter in series, you can always take the batter post off and put it there although that is the least convenient option (I would go to a fuse box first).<br /><br />Hope I didn't confuse you .<br /><br />Amir

 

[tengals123]

Re: Do I need two batteries?

thanks for the post, I still don't know which way im going to go. The electronics guy at the marine shop told me the most common way is <br />1. 2 batts ( 1 marine 1 deep cycle )<br />2. switch ( 1, 2 and both )<br />3. start on batt 1 till anchor, when at anchor, switch to batt 2 ( deep cycle ), then for the trip home on batt 2. This should keep them close to charged most of the time. So he says. How do I check the charge in each battery? Does this mean I need 2 volt gauges?<br /><br />cheers