Cable routing

[Mfr]

Is there any difference in bolting the negative from a second battery to the gearbox bell house or to the same point the original battery bolts to, next to the starter?

[Luke]

no so long as you get a good contact

[Mfr]

Thanks bud!

[F111ORY]

Hi, Dont bolt to the same point as the original battery.Another bolt at least 6 inch away. Spread the load!

[Mfr]

Hmm, OK. I will have the 2 batt's + connected to the starter then move the alternator + cable to the starter motor so that charge goes more equally to both batteries. Sound OK? I can't think why not. My Brother's factory 2 battery system just has the second battery directly connected to the first battery. Has to be better than that.

[F111ORY]

Hi, I was only refering to the negative lead!

Both positives onto the starter.

[Mfr]

Thanks, yeah. I'm thinking of the alternator cable that goes to the first battery and moving it to the starter.

[Kedishen]

Mfr, what you are suggesting will work just fine.

However, 2nd batteries are equalised through the main battery because of the potential difference in charge and have potential for high currents of 100-150amps running through the short, unfused but very thick cables.

If you go from alternator, to the starter, and branch each way to the batteries from there, it could overheat the wires - because equalising current and alternator current are traveling the same path.

Mind you, this is only in the worst case scenario of one battery being severely discharged and the two batteries equalising whilst alternator is producing energy - made worse if the dead battery is getting to the end of its life.

You could up the cable sizes from batteries to starter motor junction. Cable from alternator can be left the same.

Or you could leave everything how it is and ground both batteries to the grounding points next to headlights on each side.


Something maybe to look into is where the main cable for starter motor connects to battery. If it only gets power from one battery then you may gain efficiency by running an equally sized cable from starter to 2nd battery in the same way. Will also help if one battery is a bit knackered. Keep in mind batteries will use this wire to equalise.

[F111ORY]

For best effect batteries should be grounded to the starter or the engine/gearbox.

[Mfr]

Thanks for the advice all, I think I'm getting my head round this now. Battery 1 Negative will go to starter as it does now, Battery 2 Negative will go to gearbox. Taking your advice I will avoid joining everything up at the starter.

The two cables connecting to the starter is to share the load. The bus bar is 350amp and all cables used will be 240amp.

Thanks again!

[F111ORY]

DO NOT CONNECT AS YOUR DRAWING. Your van does not have a chassis to engine earth strap. When you use the starter the earth current from the second battery will travel through the chassis and the only route it can find to the starter earth is through the thin chassis to battery earth wire that is twinned to the battery earth lead and then down the original earth lead to the starter negative.

It will FRY the thin chassis earth and when this is burned out it will fry either the spedo cable or the clutch cable!

Connect both battery positive leads to the starter positive, you will lose power with the bus bar. Connect negative leads to the starter negative or an engine /gearbox bolt.

[Mfr]

Sorry for the bad drawing, the earth from the first battery will route as normal to just by the starter and the 2nd battery earth will bolt to the engine block. The busbar will only really have the load between the 2 batteries and the 95 amp alternator load to contend with as the positive to starters are on their own studs. But you do have me worried because the current setup has the second battery earthed to the chassis I will get on to this asap. Thanks

[F111ORY]

If a engine to chassis earth capable of carrying the full starter current is fitted then you will be OK. But such a cable is not a standard fitment.

[Kedishen]

Mfr, what is it you are trying to achieve with all of the above?

[Mfr]

Mfr, what is it you are trying to achieve with all of the above?

At the moment the second battery is badly earthed with frayed connectors and some other connectors are corroded. It does start ok but the batteries drain quickly with the LED lights in back being on. Both batteries are 750Amp Honda's and the alternator is also good. So I'm replacing the main cables and soldering new connectors at all ends. As far as I can work out the way I have drawn it is the best for what I need, I don't need split charging, just needing to improve whats there.