I have a 12’ hard bottom inflatable with a 30HP Tohatsu motor that has a 17A alternator. We use the tender extensively for fishing (running a downrigger and electronics), and catching crab and prawns. The latter involves using a powered line puller to retrieve the traps; often 400+ feet of line per trap. We prefer to not have the motor running while this is going on because this is quite beautiful country and minimal disturbance is desirable. My current FLA battery is bagged and needs replacing, and I would like to replace it with a small LiFePO4 battery.
My concern however is that should the battery be drawn down to any degree, on restarting the motor the battery could - as lithium does - draw a heavy current, possibly cooking the alternator. In addition, I do not know what kind of regulation is controlling the alternator but would bet it is not very sophisticated. Tohatsu recommends against lithium for this very reason (plus possibly also incorrect charging voltages/curves).
I just purchased an Orion XS for the big boat to integrate with my imminent upgrade from an AGM house bank to a LiFePO4 house bank. In the process of reading up on it I came across a very interesting description on the product page https://www.victronenergy.com/dc-dc-converters/orion-xs-dc-dc-battery-chargers#features which has me wondering if this might be the solution. The diagram there shows an alternator connected directly to the Orion XS which is then connected directly to the battery. Apparently the Orion can be used for current limiting AND output voltage control.
So all this leads to the question: am I interpreting this correctly to mean that I could safely install a LiFePO4 battery and protect the alternator by limiting current to say 14A and “set” the output voltage to whatever the lithium specs requires? If so, Yahoo!
Unfortunately that “diagram” is highly misleading, intended for generalized reference only. The Orion does need a Pb battery on the input. Alternator to Pb starting battery, Pb starting battery to Orion input, Orion output to leisure battery.
your main criteria for the lithium battery is the maximum discharge current: either yor line puller, or the outboard starter.
As far as regulation goes on outboard ‘alternators’, you can protect the maximum current with a fuse of ~ 20A. for voltage regulation, you can measure the maximum voltage on a charged battery -try using your current lead battery for this, unless it has a shorted cell.
I managed to connect a lithium battery directly to a small Suzuki outboard, but this only has a 6A coil for dc lighting. Max voltage was 14.2V, which is ok for the Li battery.
Thx for the reply @Mike but pretty sure you can’t fuse the line like that. If you were charging so hard that you blew the fuse, you would create a “instant battery disconnect” condition and fry the alternator (diodes) almost instantly.
The Suziki regulator self protects when the battery is disconnected. The charging coil is part of the magneto, and not a separately excited alternator. Hence there is no excitation to overshoot on a sudden loss of load. The line is also protected by a 20A fuse, which I think excessive for a 6A regulator.
Ah, thx @Mike, I didn’t know that. I’ll give Tohatsu a call tomorrow and find out what their situation is. If similar, that may provide the protection I need. Presumably the motor would continue to operate, and I guess so would the rest of the electronics, until the battery died. And in a practical sense in my situation that would not be a problem. I would be left with the problem of not being able to charge the battery so would have to remove it and shlep it into the big boat and put it on a charger. Or add a small separate charger in the dink and then just plug it into the big boat when returning.