12v / 24v system

[495v]

I have a motorguide 12v/24v trolling motor, the switch on the foot pedal has 12v, off, 24v. I'm illiterate when it comes to electrical. First of all, when the switch is turned to 12v is it only using one battery and if so which one? Secondly, the boat plug for the trolling motor is one of the round rubber looking one's with, I believe, 3 prongs on it. The guy I bought the boat from got a plug that is identical to the trolling motor plug, and wired it into an external 12v charger. By plugging the charger in to the boat plug where the trolling motor plugs in to, how do you think my batteries are charging? Would it charge one first and then the other? I know when I plug in the charger, I can hear the acid bubbling slightly in both batteries so I do know they are both charging. I will be replacing my batteries this year and want to make sure my current charging setup is working properly so I'm not replacing the batteries again next year. I eventually plan on getting an on-board charger but would like to stay with this external one for now. I don't think there is any problem but I guess I would like to know more about my setup. Thanks for any help.

 

[495v]

Re: 12v / 24v system

Well I looked into my system alittle further over the weekend. I have a charging / running plate at the bow for the trolling motor. There are 4 leads going to the back, 2 pos. and 2 neg. It doesn't appear to be either series or parrellel. I now have some new questions. 1) Will this system use both batteries simultaneously when on 12v or does it use a primary and only use two when on 24v? Next, When I plug into this plate to charge, there is a plug identical to the trolling motor plug that is wired on a 12v external charger. Is this 12v charger even capable of charging both batteries at the same time? Does anybody have this type of setup and can share some knowledge?

 

[495v]

Re: 12v / 24v system

BUMP!! Anyone HAVE THIS KIND OF SETUP?

 

[495v]

Re: 12v / 24v system

Bump again.

 

[petryshyn]

Re: 12v / 24v system

Is the charger 12 volt?<br />Are there any switches added to the wiring that comes from the charger?

 

[495v]

Re: 12v / 24v system

The charger is 12 volt. The plug that is wired in has four prongs that plug in to the charging / running plate at the bow. I inspected the plug and found that the positive from the charger is shared with the two bottom prongs ( both positive leads to the batteries) and the negative from the charger is shared with the two top leads (the negative's to the batteries. Any other info. The only switches involved in the wiring that I can see is the plug that's wired into the positve and neg. of the charger, which plugs into the charging / running plate on the bow, 4 leads go back from there and run through a circuit breaker and then to the leads on the batteries.

 

[h2oTherapy]

Re: 12v / 24v system

I am no expert on trolling motors, but my business uses battery back up system all the time. I have seen systems that are similar to the set up you describe, and the selector switch will change the leads from the battery from running in parallel (12 volt) to series (24 volt). You can check for this by removing all leads from the batteries, and attach a continuity tester to both positive leads. When the selector switch is set at 12 volt, the leads should have continuity between them, when at 24 volts, the leads should not. If this checks out I would say that both batteries are being used for both 12 and 24 volt the selector switch mearly changes the battery configuration from parallel to series. The other difference will be that you will have more current capasity running on 12 volt.

 

[495v]

Re: 12v / 24v system

That makes sense, but what about the charger. If I disconnect the trolling motor plug, which I believe your talking about the selector switch on the foot pedal, Does it charge the batteries like a 12 volt, parrellel system automatically? Also what do you mean by more current capacity running on 12v.( longer running time?)

 

[h2oTherapy]

Re: 12v / 24v system

495v,<br />Since the charger seems like it has leads going to all 4 battery terminals (2 pos, 2 neg) I would say that it charges at 12 volts (which is common for lead acid chargers)and charges both batteries at the same time. Not being an expert on trolling motors, I don't know if the motor can run on both 12 and 24 volts (thats not typically seen on DC motors, but not unheard of). Is it possible that the motor runs on 24 volts, the charger charges at 12 volts, thus the reason for the ability to switch between both? Don't know for sure.<br />Current capacity: Longer running time in the sence that a 12 volt motor running on 2 batteries will run longer than 1 battery. But a 24 volt motor must have 2 batteries to run at all. (Clear as mud right?!) I think my neighbor has this set up on his boat, I will try and take a look at it to understand it better, I don't want to get you off on the wrong track.<br />regards, h2o

 

[495v]

Re: 12v / 24v system

Thanks for the input there h20. Any further info is much appreciated. What you are telling me makes absolut sense. I will try the continuity test within the next few day's to see what happens, but I'm curious as to the charging aspect. Just put 2 new batt. in and would hate to eat them up. Anybody else that can share some advice or knowledge?

 

[495v]

Re: 12v / 24v system

Well I didn't do the continuity test yet, but after going out over the weekend I checked the batteries. I was running on mostly 12v all day and when I checked the batteries one was at 12.53 volts and the other was at 12.69 volts. Wouldn't this lead me to believe that when the switch is on 12v, I am only pulling of the primary batterey and not off of both as in a parrelel setup? Considering this, would it be better to run on a low 24v speed than on a high 12v speed? If I do run on 12v, would you recommend switching the batteries around every so often to keep similar charge cycles on them?

 

[h2oTherapy]

Re: 12v / 24v system

495v,<br />Sorry I haven't got back to you, got called out of town last week.<br />Thats a good point about the voltages, if they were wired in parallel, they would almost have to be at the same voltage (by laws of physics anyway). If what you suspect is correct, (running off 1 primary at a time), then rotating the batteries is probably a good idea.<br />The life span of a lead acid battery is largely determined by the number of charge/discharge cycles, and the lower you discharge it, the bigger the effect of this is. Deep cycle marine batteries are better than common car batteries for just this reason. They design them to withstand deeper discharges, but even so, the deeper the discharge, the shorter the life. Probably more than you cared to know......<br />h2o.

 

[495v]

Re: 12v / 24v system

I'm going to run another test this weekend. I plan on running on a low 24v speed and then check my batteries at the end of the day to see how far they dropped. I think I'm going to end up keeping a chart and rotating batteries every few trips. We'll see what my next test brings. What percent do you think my battery is at when it dropped to 12.53v?

 

[h2oTherapy]

Re: 12v / 24v system

Its really hard to tell. Batteries have very flat discharge curve, that means that for the first 90 % of a given cycle they might drop 1-2 volts, but the last 10% they drop to 0 (eventually). Whats equally important, in addition to where they are at the end of a trip, is how much they dropped during the trip (where did they start). Very Good idea to do your own testing. You know what they say: In life, theory makes better explantions, than predictions. (In other words, don't rely on what I say, go and check it for real) <br />regards, h2o

 

[495v]

Re: 12v / 24v system

Thanks for the input. Before I went on my last outing they were both at 12.69. I plan on checking them again before and after my next trip. I read on a post here that at 12.7 volts you are fully charged and at 12.5 volts you are 50%. Does that seem reasonable?

 

[petryshyn]

Re: 12v / 24v system

495v<br /><br />This may ruffle some feathers. You can't accurately determine "state of charge" on your battery until you determine a reference voltage from your existing battery. You must fully charge your battery, let its it for a few hours, then measure its OCV (open circuit voltage). This voltage will indicate fully charged for future reference....Even using a hydrometer requires the same technique.<br /><br />To determine if the charger is charging both batteries, simply measure the voltage across both batteries when being charged and compare their voltages. If both read around 13.5-14 it means they are hooked in parallel. If only one reads 13.5-14 and the other reads less (12.?) Then only one is being charged.

 

[495v]

Re: 12v / 24v system

Thanks Schematic, I don't know why I didn't think of that. I will try this test and post results. Thanks again.