Charge from 6hp Tohatsu

Discussion in 'OnBoard Electronics & Controls' started by 23feet, Jun 19, 2015.

  1. 23feet
    Joined: Dec 2014
    Posts: 73
    Likes: 11, Points: 8, Legacy Rep: 10
    Location: Bay Area

    23feet Junior Member

    OK, I should chip in here as the original poster. I have become familiar with the idiosyncrasies of the Tohatsu charging over time and (sometimes) with helpful advice from others. The sail pro has a rectifier and alternator that charges up to 5 amps. The equipment is robust, and the only problems I have had are from bad connections (my fault) and ignorant misuse of multimeters (my fault). The funky voltage reading with a multimeter is "normal". The only way to read the amperage is the conventional test of disconnecting the positive wire to battery and clipping in the multimeter in series (one lead to positive disconnected battery wire and one lead completing the circuit to battery). With the multimeter in series it reveals that the sail pro charger produces around 4 amps even at low revs, and increases to about 4.8 amps at high revs - in other words it works great. The standard supplied alternator output wires do NOT have to be connected to the battery - nothing happens if they are not. I once did the ignorant noobie mistake of reading the amperage directly from the output wires to my multimeter (that is, short circuiting the charge current). It blew the fuse in my multimeter. Note that there is a 10 amp fuse on the outboard charge output that can also blow if you cause a short. Hope this helps.
     
  2. paul_ap
    Joined: Feb 2020
    Posts: 2
    Likes: 0, Points: 1
    Location: Greece

    paul_ap New Member

    I tend to agree. I wrote to the factory in Japan hoping for an authoritative response, but sadly they forwarded my question to the local importer so that I would get a local answer. Their answer was that it is 'suggested' that the wires always be connected to a battery, for the avoidance of possible problems.
    I did get confirmation that the output voltage is regulated, however (this is also confirmed by Tohatsu USA).
     
  3. 23feet
    Joined: Dec 2014
    Posts: 73
    Likes: 11, Points: 8, Legacy Rep: 10
    Location: Bay Area

    23feet Junior Member

    The mysteries of the Tohatsu alternator continue..... I installed a digital current/volt meter on a shunt and found that the alternator/charging circuit is only putting out 0.2 amps at full throttle and up to 0.5 amps at idle. I thought this must have been some sort of wiring problem on the amp readout so did a one hour test run at half throttle on the outboard. The total amps went from 61.66 to 61.88 (after an hour ) confirming that the readout for charge current is correct. The resting voltage went from 12.51 to 12.54 - this is on a bank of 2 X 35ah U1 batteries in parallel. I though that I might have inadvertently fried the rectifier so tried a new one - same result.

    Does this mean that the output amperage is conservatively limited until the battery voltage is very low, or that I have something wrong in my alternator charge circuit?

    Many thanks (again)
     

  4. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 47, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Morning 23Feet, I saw your question on my phone in Cape Town and could not log n. Sorry for the delay.
    You have to understand Lead acid batteries. The charging voltage is normally at around 14,4 Volt and produces the highest charging current for the battery. When the battery gets fuller, the current drops to a lower amperage. The voltage rises to 13.8 Volt (gassing voltage when the battery start "boiling" your acid liquid. at temperatures of 25 degrees Celsius , but in a very cold area like Alaska with extreme low temperatures below zero the gassing voltage drops to below 13 Volt and in countries with very high ambient temperatures the gassing voltage increased to above 13.8 Volt. Thus that is the level that a good battery charger will cut the current to maintaining current of very low current. i.e, yes with a empty battery the regulator will supply high currents and the regulator should cut the current when the battery gets fuller to a trickle charge current. A large battery , deep charging or a normal car battery has a small leakage current which "empty" the battery over time. A 7 Ah 12 Volt battery normally after 3 months, a large battery after approx 2 months and depends whether there are items like alarm, security etc is connected to the battery which drains the battery faster. A lead acid battery start charging at 12 Volt. (depending ambient temperature while a lithium batter starts charging a battery at 8 to 9 volt already. Bert
     
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