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Date:         Fri, 28 Jan 2000 13:40:36 -0800
Reply-To:     andrew swingler <andys@ECE.UBC.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         andrew swingler <andys@ECE.UBC.CA>
Subject:      more ???? Re: Diesel alternator
In-Reply-To:  <4f.b599b8.25c34f41@aol.com>
Content-Type: TEXT/PLAIN; charset=US-ASCII

I've always wondered about the charge control for auto batteries. I suspect that there is no curent control on the alternator, only a voltage regulator. If this is true then the only thing regulating the current is the voltage drop along that red charging wire (to the starting battery). More current = more voltage drop = lower battery voltage until some charging equlibrium is acheived. That being said putting in a larger alternator will not increase your charging rate unless you run a larger cable direct from the alternator stud. If you connect the aux battery via the charging wire on the starting battery (through a relay or isolator, by the way the isolators drastically reduce the charging current by inserting the .7V diode drop.) it should not overload the charging system because of the effect described above. Assuming that your aux battery is of the group 24 varity (almost fits under drivers seat) charging current should be kept below 100AH(approx size)/10 or below 10A anyway but no one seems to use a current regulator to prevent over currents to battery.!? This being said I would be careful about running that heavy gauge wire directly from the alternator and stick with the stock length of red wire that runs to the passenger seat. 14V from a 65A or 90A alternator through a heavy gauge wire to an empty 100Ah size deep cycle battery would result in some very dangerously large charging currents.....I think. I think my points are: 1) You don't need a heavy duty alternator to recharge a 100Ah battery that only requires a 10A charge current 2) Becareful about connecting empty deep cycle (RV and marine) batteries to the alternator through a low resistance wire and no charge controller (curent regulator), currents could be dangerously high. 3) If all your loads combined exceed 65A then of course you need a larger alternator.

I have my aux battery under the drivers seat and use a relay and the charging wire from the starting battery. I have been monitoring charge currents and everything works fine with no need for the charge controller. I don't experience any charge currents above 15A even when the battery is charged from completely dead.

That reminds me, install a fuse on the aux charge wire. 20A is good for group 24 size batteries. This could save your alternator against large battery charge demands.

Hope this makes some kina sense.

ANdys Vancouver

On Fri, 28 Jan 2000, Ken Hunter wrote:

> I would like to increase the output of the alternator on my 82 diesel Westy > for 65A to 90A to help charge the aux battery. I've heard this was an easy > upgrade but no one knows the particulars that I've talked to. Advice? >


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