[Mee-n-Mac]

Originally Posted by Fish'n John

The batteries are both good. I had them checked under load and replaced one late last year. The connections are all clean and tight. I think it is clear that the charger is not working at 24v but the one question that keeps nagging at me is why it didn't output 24v as it first came back from Expo North. Could they have rewired the charger for 12v at each set of terminals?? Certainly if it had worked right in 1998 they would have burned up the existing wiring if they had run it the way it "appears" to be hooked up. I think I have to pull that battery charger for a look inside before I take it anywhere. What do you think?

I agree, it sounds like they wired it for a 12V motor and that's the only way it's been operated all this time (new trolling motor [TM] being better than old TM even at 12V). As for the ignition SW being in the accessory position ... I read a thread that said the charger had another set of wires to the main, boat battery and that when the ignition was on, it would parallel all the batts so as to charge them up off the engine's alternator. I'm not sure how well this would work but it sounds like the charger is breaking the series connection btw the batts and paralleling them when the ignition sw is in the accessory position. I'll guess this is proper for the moment. Now as to why you get zero volts ... at first glance it seems there's only 2 possibilities : the charger is broken (not making the series connection) or the terminals are mislabeled.

On the latter ... pretend due to a mislabelling you connected the batts with the 2 pos terminals tied together when trolling (via the internal series connection). Then if you measured (on the charger) btw the neg and 24V output you'd see +12 added to -12V (minus voltage due to the batt reversal) and get 0 volts out. This would mean you'd never be able to run the motor off the batts though and at some point it did work if only in "12v mode". Moreover when the batts are in paralleled to charge, you'd have the 12V reversed going to the mislabelled battery and that, absent any internal protection in the charger, would be a very bad thing indeed. This possibility sounds like it's ruled out then.

Thus I agree it sounds like the charger isn't making the serial connection when it should. But if this is the case, then with only 2 wires going to the TM from the batts/charger, then there would be no voltage due the missing serial connection. Again at some point both TMs ran, if only at some lesser voltage perhaps. So I'm beginning to think you have a wiring issue and a maybe a half working charger. Did you notice how it was wired when it came from Expo North ? I'll guess (again) perhaps they had it wired somehow for 12V operation only.

I agree that #14 wire is insufficient to run any TM off of, so the wires burning up (at 60A) isn't a surprise ... though ... if the charger is supposed to make the series connection btw the batts, then the wires (2 of the 4 to be exact) connecting the charger to the batts would be carrying the full current through them. AWG12 might just work for a small run but I wouldn't trust it so I doubt the charger designer would have either (at 60A). The rule I read is 1A for each lb of thrust at 12V, half that at 24V. But let's take your TM's book at face value and say it's supposed to draw 60A. Hence the smoked wires. The AWG8 should have been OK but the melted connector is troubling. Unless it was corroded and making a "high" loss connection, then the melting at 60A would be understandable. I get the gut feeling there's something I'm missing here ...

The way the old systems worked was to deliver 24V to the TM. If you wanted less than full speed, the TM controller added resistance in series with the motor, thus decreasing the current draw and also reducing the voltage seen by the actual motor itself. If you kept reducing the speed, increasing the resistance, at some point the motor would have less than 12V across it. So the old 12/24 systems would switch out the series resistance and 24V, and connect 12V, perhaps through a lesser series resistance, to the motor. It saved the battery this way and allowed a finer low speed control. The question for you is where this switching is taking place, if indeed it is at all. Newer TMs come with pulse width modulation (PWM) speed control and don't have any voltage switching. I do worry that your old charger might not be rated to handle the newer motors current. May I assume it came with 30A fuse ? That the new(er) TM came with the 60A fuse but that it wasn't installed when you brought it to Expo North ?

What other wires come out of the charger to ... well, any place ? What are the labels on the wires ... or terminals on the charger ?
How many wires run to the TM controller; 2, 3 or 4 ? What gauge would you guess they are ? What MK TM do you have ?
Lastly I'd think the series/parallel connection internal to the charger would be made by a fairly hefty relay or solenoid. Can you hear a good click or clunk when the ignition switch is turned from off to accessory (or on) ? Or going back the other way, accessory to off ?

If you feel inclined and have some electrical saavy, take the charger inside. It sounds like you have a complete manual for it. I'm not sure how well trouble shooting over the forum will work but you've got my curiousity aroused now.

Here's my guess at how the system should work. When AC power is off and the ignition is off, the relay switch goes to it's unpowered state and the batts are connected in series (internal to the charger) and you should see 24V across the proper terminals (assuming the right connections to the batts). This voltage should go to the TM on 2 hefty wires (AWG6 or 8). The TM then works off the 24V as it's designed to. When the AC is on or when the ignition is on (really shouldn't be accessory but ...) the relay switch is energized, the series connection is broken and the parallel conenction is made. I'm assuming there's another pair of wires to another battery (the main boat batt) that you haven't mentioned. The TM batts are then charged off the AC/DC converter or from the engines alternator. The voltage at the 24V output would then also be 12V, same as across all the + to - battery terminals. The charger should have 2 current "ratings"; one at which the batts are charged (perhaps 5 - 10 amps) and a max current when the TM is being run. Ideally the TM connections are made to the batteries themselves and not to the charger terminals. If it's done at the charger then all the wires from the charger to the TM batts need to be "hefty".

FWIW here's a nice chart and online calculator for what wire size is needed and how much voltage drop can be expected for a given current draw and AWG ... http://www.powerstream.com/Wire_Size.htm

Here's a simplified diagram of the wiring paths in each mode; when trolling or when charging. Note the fat lines indicating where the max current is supposed to flow.