Myths and facts on Dual battery setups.

[rwells9999]

Hi all,
I’m in the process of fitting my center console with a Dual battery system and have had a look at some of the questions and comments placed onto this web site. Just to give my comments some credibility, I have been an Electronics tech for the best of 22 years and have spent the last 12 years in IT so I hope that I can remember my Ohm’s law. Firstly the myths about how much current your electronics is drawing. If you are unable to measure the current drawn by a device or don’t have the manufacturers specs, then using the rating of a fuse is a poor indication of how much current the device draws. There is NO hard rule or formula on manufacturers as to how they rate fuses. If a piece of equipment has a 5 amp fuse (depends on type of fuse) then you can only assume that the current consumption of that device once it has settled down would be 40 - 50% of that i.e. 2 amp. So when I see people place comments on the web about a sounder using 5 amps I think that is a bad guess. I have had a look at the manuals of some of the popular Sounders, GPS’s and Radio’s and this is what I have found.

Furuno 600L color sounder # # # # # #1.3A with full backlighting on
Humminbird Paramount wide sounder # # #0.6A (No specifications figures available)
Lowrance LCX-15MT GPS/Sounder # # #2 to 3 A (No specifications figures available)
Navman 4500 sounder # # # # # # # # #0.8 A with full backlighting on.
Garmin 182 GPS # # # # # # # # #0.4 A
Navman 5100 GPS # # # # # # # # #0.6 A with full backlighting on
Icom M45 VHF radio # # # # # # # # #0.8 A in standby. 6 A in high power Tx.
GME GX294 27 Mhz # # # # # # # # #0.35 A in standby, 1.6A in Tx

OK you can see that the real power users if only for a short period of time are the transmitters in radios, GPS’s have no power circuits in them and as such use bugger all power. Sounders, well some use more than others.
Now for the outboard myth. For those who have a 4 stroke outboard, you may think that it can put out some colossal amperage and charge your battery quickly, WRONG. The modern alternator charging system is designed to be kind to batteries. The system relies on the condition of the battery itself to determine the current flow, only the voltage is regulated. A discharged or partly discharged battery will consume a relatively high current for a short time only until it reaches a state commonly referred to as “surface charged”. The current it demands then drops to a lower value, typically around 5 amps. This equates to a 100 amp/hour battery that is half flat, taking 8-10 hours of engine running time to fully charge. In a situation when power consumption may average 5 amps constant, the total capacity of an auxiliary battery may be used in less than one day. Running the engine for a short time (even up to two hours) WILL NOT come near recharging that battery.
As for 2 stroke outboards, most like my Yamaha 70 have a rectifier and are only capable of delivering only about 5 amps. Maybe the 4 stroke has the edge over the 2 stroke as it is able to bring the battery to the “Surface charge” quicker, it’s chalk and cheese.
After doing all this web browsing I have come to the conclusion that I will be leaving my starting battery which has a CCA (cold cranking current) of 700A as is, and adding a lower current deep cycle battery as the auxiliary. I’ll be employing a ‘BEP battery management cluster’ with a voltage sensitive relay. In my case the wiring changeover should be relatively simple as I wired a separate cable form the main isolation switch to run all the electronics and lights. This cable will now come from the auxiliary battery. As can be seen from the figures that I #have provided, current drawn from an auxiliary battery for a typical setup would be around the 3 to 5 amp mark and maybe double that if out at night with navigation and cabin lights on. I hope this has cleared up some of the guesswork that seems to be rampant.

Robin

[Big_Kev]

Good info there Rob but I think you may have made it worse for many.
But you started this so you will now have to answer the barrage.LOL
Cheers Kev

[aido]

good topic robin,
thanks for researching it.
my furuno 663 video sounder is quoted as
less than 25watts (2.1 amps) max. near double the
lcd unit? i'm switching it off anyhow when anchored.

what about this then??
2 batts and an isolation switch 1, 2, 1+2, and off.
having one deep cycle and one "normal" high cca type
is my new setup. an accurate voltmeter might be more usefull than an ammeter though, thats what i'm using and know exactly when to switch over!
(battery voltage relationship to state of charge)

could you maybe tell me the myth or fact about using this dual setup with mixed battery types, should they be used
isolated because of the different charge /dicharge characteristics. i am going to leave with both fully charged and use batt 1 on the way out then use batt 2 on the way in, or just use batt 1 down to 11volts then switch to 2.

do you envisage any problems trying to charge them in parallel ie, batt switched to the 1+2 position?

[webby]

Hi, Some interesting facts there Robin, i run a dual system on my rig, with has a 130 2stroke, due to previous battery problems and having replaced both in the last few months.
I now use no 1 just for starting, and no2 for any accessories. If doing a overniter, i now carry 2 of those house alarm batteries which will run my fluros easily for up to 3 nights, and use no2 for radio/anchor lights and sounder while at anchor.
I also found that if you do a lot of stop starts over the course of a trip. I always run with no1 taking the charge. i would have to do 6 circuits of the bay at least to at least put any resemblance of a charge back into the starting battery.
regards

[Lucky_Phill]

I'm with you aido. I have a 668 Colour unit, and with out knowing the specifics, it uses a lot of power.

I too switch it off at every possible moment.

Although, since swapping to the Honda 4 stroke, the charge in both batteries have been good ( not needing the top up from the land based charger ). Apparently the Honda runs an alternator setup and can shove 45 amps into a battery at 5000rpm.

Any thoughts on this Robin ?

Good info, by the way and thanks for sharing your ' expertize "........

Phill

[Lucky_Phill]

From what I've seen Brian, you normally do .....10.....laps of the bay every trip ! ??? ;)

Phill

[spike2]

lam interested in having both my batteries at full charge each time l go out , but l have no electronics understanding . is there a product available that l can simply plug in when l get home forget until the next morning and wake up knowing my batteries will be fully charged , as opposed to under charged or cooked

cheers spike

[Kerry]

Well much of the power issues are generally highly over done.

I've never had a battery fail prematurely and have simply replaced them just becuase the stamps on the terminals start saying they're 4-5 odd years old and that starts to play on the mind (mainly).

Only have 1 battery (on each engine ;)) but if one followed the thinking schema then I'm probably 1 sort of a battery bank.

Obviously the complete setup is quite flexible and can shove both batts on to one or either engine if required but considering running 3 radio's, 2 sounders (one of them is a 667), 2 GPSr's and all the other bits and pieces the need for a "second" battery has never been proven.

I realize twins are a slightly different situation than a single engine and although the capacity is always there it's simply never been needed.

Cheers, Kerry.

[drevil]

I recently set up 2 batteries, and on the switch (1,2, 1+2, 0) there was a set of contacts for "field". There was not wiring diagram with this switch, but I read somewhere that these field contacts are for connecting an alternator (?) wire so you don't blow anything up if you accidentally swith it to 0 when running the motor.

I haven't wired this up, mainly 'cos I'm not sure what wire I'm supposed to connect. What's the consensus, does everyone hook up these wires (where the switch has contacts for them)?

Should I do the same? What wires do I connect?

[rwells9999]

Hi all,
Someone has asked a very good point about charging 2 batteries which are of dissimular type. I have had a quick look and there may be a problem with this, I may have to revise my own setup. I will try and get some more info asap. One other topic raised it's head, some 4 strokes have the ability to deliver high currents into a load or battery, the battery will only recieve this high current for a short period of time till it reaches it's "Surface charge" and will then drop back to a much lower charge current. Will get back with some answers soon.
happy boating, Robin

Sunday, 2/8/03
Hi guys,
Since I posted this article and the interest that it has generated I thought that I would post what I have done and the results. I ended up fitting a BEP 'Battery management cluster' with a 'voltage sensitive relay'. The secondary battery that I chose was a Delkor 70 amp deep cycle. I figured with all my electronics turned on and the radios (2) in mute, the total current drawn would be about 6 amps, I allowed myself a 30% margin on top of this, that's now a total just under 8 amps. I went out today for a short trip and monitored the terminal voltage on the secondary battery. The voltage sensitive relay performed perfectly and kicked in the secondary battery when the terminal voltage rose above 13.7v. The total cost of this exercise was about $380. Peace of mind comes at a price.
Happy boating.
Robin

[aido]

hi robin,
the solution i see sometimes is to charge each battery
via a silicon power diode capable of carrying the maximum
charge current, ie >20 amps for a flat battery.
a $6 35 amp bridge can isolate both batteries charge circuits nicely.
BUT this worsens the ability to quickly charge either battery
due to the voltage loss (.7 v) across the diode. if the supply alternator
is marginal then i suspect the high cca discharge battery will still 'hog'
most of the power available!!!
seems having matched batteries is a better solution but then will it be 2
'normal' batteries or 2 deep cycle types???
it's a quandary then having a high cca starting battery and a nice deep cycle
unit for the accessories. very interested if you can dig something up robin.

regards, aido.

btw, whatever happened to those 12 volt 'switch' batteries (exide??) that had
a small reserve section to get ya going if the main section died? that would be
great for those single battery boaties.
don't forget the rope and practice a pull start now and then.
hand starting a 200hp v6 seems daunting but apparently can be done.

once had my 90hp yamaha starter motor die at peel. damn near took over
an hour of hard yakka to fire up. that's when i found the manual choke
control. first pull... doh.

[Lucky_Phill]

Between you Aido and you Robin, would it be possible to draw up ( for those electrically dysfunctional people like us ), a wiring diagram for a dual battery system.

This question of dual batteries pops up quite often here, and needs drawing rather than an explaination.

I'm sure all boaties would appreciate it.

What ya reckon guys ?


Phill

[jaybee]

I have one that someone sent to me (krazyfisher i think) that is fairly easy to read, still havent got around to it tho. Heath has a diagram on his site, it confused me tho, but thats easy enuff done. I'm a sight person that needs lots of colours and each one numbered. #[smiley=help.gif]
cheers

[rwells9999]

Hi all,
I have been busily researching into the pro’s and cons of mixing different types of batteries. I spoke to a technician from Century batteries today and posed the above question. His reply was that there was no reason why you could not mix a standard wet cell battery with a deep cycle battery. But made a couple of points.

1. A conventional alternator would not fully charge a deep cycle battery as the alternator would not have the ability to deliver enough volts (15.2) for the battery to obtain a gaseous state and fully charge.
2. Deep cycle batteries have a different charging curve than conventional batteries, and as such take longer to charge.
3. He indicated that it was a good idea to charge a deep cycle battery from a shore charger every month or so.
4. I also posed the question of electronic solenoids for the purpose of automatic switching, his response was that these were a good idea but nothing wrong with conventional manual switches.
I have browsed a lot of off-road 4WD sites re theses topics and they have all come up with the same answers.
From what I have seen on this issue, there seems to be a lot of guesswork going on. I know not everybody can be an exspert in this field, but if ya want to dabble in these things called boats then it’s up to you to know how they work (and sometimes don’t).
Robin

Every effort to present accurate data which has been obtained from various automobile manufacturers and published information sources. While I believe these sources to be reliable and have taken every precaution in its compilation, I cannot assume responsibility for any inaccuracies in print or specifications or the advice given therein.

[aido]

this is the setup i've got.
important never to select off with the engine running,
http://members.ozemail.com.au/~dessaix/dualbatt.jpg

i'm not much of an artist.
here's a nicer pic at this link,
covers other installations as well.
cheers, aido.
http://continuouswave.com/whaler/reference/dualBattery.html

the downfall with my setup is to charge both batteries then
the switch must be in the BOTH position. then back to the problem of different battery types comes to play.
here's something i just found in a search,

http://www.hellroaring.com/images/Outboard%20with%20backup.jpg

similar to the diode fix i mentioned earlier, but did not advise. i prefer to keep it simple for now.
thanks for the battery info robin, maybe i'm concerned for no good reason about their differing characteristics. :) .

[aido]

and one last link that gave me a laugh,
just check the dash mounted isolation switch, lol.
he does have some good faq's for boaties though
and addresses the high cca and deep cycle problem
in a roundabout way.
http://www.pirate4x4.com/tech/billavista/dual_battery/my_dual_battery_setup.htm

[Kerry]

Which, what and where do the outboards start that have independent secondary charging circuits.

Cheers, Kerry.

[Lucky_Phill]

That....continouswave site was pretty informative.

Thanks guys


Phill

[Big_Kev]

The dash mounted switch is a doozy. And the wiring under the bonnet left me wide eyed.
Kentucky fried Jeep.
Cheers Kev

[rwells9999]

Ya Aido,
I think that the BEP Voltage sensitive relay that you can buy for $89 is all that in one small neat package. These days I cant be bothered stuffing around with descrete components, not at that price.
Robin

[ozzyfisho]

i have a loose wire going to the positive and one to the negative terminals. these both have exposed metal at the ends. to test the level of charge in my battery i just put the exposed ends of these wires on my tongue. it makes me dance like michael jackson and it tastes like burnies ;D ;D ;D

seriosly though, i hate to stray from the charging topic but does the wiring on a boat need to be earthed. is so, to what do you connect the earth wire.

also do 4 strokes drain less power when starting

[rwells9999]

Have a look a a previous posting for what I have done. Here is the final install.I haven't shown the secondary battery
Robin