Deep cycle batteries connected in parallel
Deep cycle batteries connected in parallel
(OP)
Guys-
I'm a mechanical engineer. My electrical engineering knowledge stops at Physics III and Circuits I so I'd appreciate it if you could keep it simple. What I'd like to know about is the feasibility/desireability of connecting two (or more) 12VDC deep cycle batteries in parallel in an effort to boost the total amp-hrs available to an electric trolling motor. I have vague memories of someone saying that this is not good for one or both of the batteries. Is this true and, if so, is there a simple circuit that will protect the batteries but still come close to doubling the number of amp-hrs that would otherwise be provided by a single battery?
I'm a mechanical engineer. My electrical engineering knowledge stops at Physics III and Circuits I so I'd appreciate it if you could keep it simple. What I'd like to know about is the feasibility/desireability of connecting two (or more) 12VDC deep cycle batteries in parallel in an effort to boost the total amp-hrs available to an electric trolling motor. I have vague memories of someone saying that this is not good for one or both of the batteries. Is this true and, if so, is there a simple circuit that will protect the batteries but still come close to doubling the number of amp-hrs that would otherwise be provided by a single battery?
Tunalover





RE: Deep cycle batteries connected in parallel
There is a "battery engineering forum" where some more people can give opinions.
RE: Deep cycle batteries connected in parallel
TTFN
RE: Deep cycle batteries connected in parallel
RE: Deep cycle batteries connected in parallel
You get what you pay for. If you ignore good engineering practice, when the sh*t hits the fan, the failure will be spectacular and expensive.
TTFN
RE: Deep cycle batteries connected in parallel
For your application there is no reason you can't parallel two batteries. Putting batteries in series is a lot bigger problem. All most all "cruising" sail boats put many batteries in parallel and cycle them heavily for years
with few problems. I would not hesitate to do it. If you don't run them way down all the time you will get better life out of them to boot.
I have done this many, Many, MANY times.
Always recharge them as soon as possible.
I would recommend that they be the same brand and preferably the same model. But if not then they MUST be the same chemistry! Gel or flooded, etc.
RE: Deep cycle batteries connected in parallel
(1) Replace both batteries together even if only one is "dead"
(2) chaeck that your alternator / charger can cope with double the load when charging.
RE: Deep cycle batteries connected in parallel
Paralleling a couple of batteries to increase A-hr is very common and there are few significant issues.
Chargers and alternators should self-limit their current to their own capability - otherwise they'd blow up the first time they met a dead battery. This is not an issue. The charging current doesn't automatically double for two batteries in parallel, but the charging time may double.
If one battery dies early (for some reason), then there may be no reason to replace the other battery. If it dies of old age, then perhaps you'd want to replace both at the same time.
If the batteries are kept in parallel then they'll obviously have the same voltage. If one does discharge into the other, there will be some loss. But once they're equalized, then this isn't an issue any longer.
Don't parallel connect a fully charged battery across a dead battery because the charging current between the two batteries might be incredible.
Watch out for hydrogen build-up.
Don't accidently connect one battary backwards (putting them in series). Make sure you have lots of light in the battery compartment so you can see.
RE: Deep cycle batteries connected in parallel
RE: Deep cycle batteries connected in parallel
On another note, sort of touched on by VE1BLL, two batteries in parallel can drive you nuts when one dies, as they both may read the same voltage but one may have zero capacity. So make sure you have a way to isolate them for testing. And test them individually at the first hint of any problem or you will be murdering the good one by radically discharging and recharging it, since the other one is there in *looks* only.
I have a diesel with two batteries in it, in parallel, and have learned this little tid bit first hand.
RE: Deep cycle batteries connected in parallel
Batteries, and even deep cycle batteries, when they are called for are commonly mounted in parallel, 2, 3, and 4 at a time on over-the-road transportation equipment such as trucks and busses. Why even my diesel pick up truck has two batteries in parallel.
They do their job, and alternators recharge them day in and day out, often without knowing how many batteries are in the battery compartment. They get changed out individually, and as complete sets. Not a big deal. (I prefer changing out by sets, but have done it individually with success.)
While a lot of theory has been thrown out here, and some good caveats given, practically speaking, there is no problem, tunalover, with your paralleling 2 12V batteries in order to get more fishing time in with your trolling motor. Enjoy yourself, and think about fishing while you are out there, not engineering.
rmw
RE: Deep cycle batteries connected in parallel
I have for years paralleled a group 31 and a group 27 12V Deep Cycle battery on my boat. I do not usually run more than one at a time except during "charging." I have a make b4 break switch (MFG'd by PERKO) that allows switching during engine on operation. Although I do not have one,"battery isolators" are also available to prevent one from killing the other. (At least that is what I think they are for, not sure though....never needed one).
See, I use mine for obscene stereo operation. READ: Providing tunes for everyone else out at the island or sandbar on our local lake. I do not know what your trolling motor draws, but my twin amps draw over 30A each. This lays waste to the group 31 within a couple of hrs. I switch over, start up, switch back and recharge. I cannot use 2 grp 31's because of space limitations. The only problem I ever had was last year. I was charging and I was also running the stereo up and it caused the 50A main in the alternator ckt. to trip. Oh...had some wires get a little too hot as well a while back!
I have to disagree with whoever posted "They dont like serious discharge cycles, and you will probaly end up changing them quite often." I was led to believe the opposite, that deep cycle batteries dislike shallow charges and thrive on a full to low charge, and then recharge cycle.
Anyway, in 1999, my boat tunes registered at 117db as opposed to the 114db @ the drivers seat of my challenger, in the beautiful, hot summer day. The canvas up makes it beyond something I can measure (or tolerate MYSELF (db meter max @126db)).
I cannot recommend that anyone reading this post attempt this with their stereo's at home or otherwise. Hearing damage can result and it may aggitate your significant other as well! Hmmm......what was that she just said?
Scott
In a hundred years, it isn't going to matter anyway.
RE: Deep cycle batteries connected in parallel
RE: Deep cycle batteries connected in parallel
Tunalover