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SIZING BATTERY CABLES
Battery cable size must meet the increased output ca
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pacity of your new alternator. The easiest method for
determining the best cable size for your system is to
compare your new alternator’s rated amperage output
and the ROUND TRIP length of the cable running from
the alternator to the battery being charged, and back to
the alternator via ground to the chart at right.
Cable length requirements may also be calculated with
the formula CM=K x I x L/E (whereas CM represents
the circular mil area of the conductor, K represents the
mil-foot resistance of copper, I represents current, and
L represents the length, in feet, of the round-trip cable
run and E represents voltage drop in volts). When using
this equation, a K constant of 10.75 indicates copper’s
mil-foot resistance and voltage drop should be calcu
-
lated at 3% (0.36V for 12V, 0.72V for 24V).
BELT SIZE REQUIREMENTS
Your Balmar alternator demands more horsepower than
your standard OEM alternator. This additional load may
require that you replace the standard drive belt with a
heavier-duty unit. Many aftermarket belt manufacturers
supply premium quality belts, designed specifically for
heavy-duty marine and industrial applications. Among
these are the Green Stripe belt by Gates and the Top
Cog belt from Dayco. In addition, many auto parts sup
-
pliers, such as NAPA, carry extra heavy-duty belts de
-
signed to support larger horsepower loads.
As a rule-of-thumb, we recommend a minimum 3/8" belt
(measured across the back of the belt) for our 70-amp (12-volt) alternators. Minimum belt width for 100-amp alter
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nators is 1/2". Any 12-volt alternator larger than 100-amps or 24-volt Balmar alternator will require dual belts or a
flat, multi-groove belt for optimal performance, as well as acceptable belt life.
BELT TENSION
Under or over-tensioned belts can result in belt slippage, premature belt wear, alternator overheating and belt fail
-
ure. Typically, belt deflection should be between 1/4” and 3/8” when you push your thumb down on the back of the
belt at mid-span between pulleys. For more precise tensioning adjustment, use a commonly available tensioning
gauge. The use of a belt tensioner, or pulley jack, makes it easier to adjust the belt tension by using mechanical
means to push the crank pulley and the alternator pulley apart. One such device, sold by MSC Industrial Supply
1-800-645-7270 (Part. # 35438209) is designed to provide “hands-free” tensioning for V-Belts.
FAN ROTATION
6-Series, XT-Series, AT-Series and the 97EHD alternators feature dual internal cooling fans, and are designed to
provide maximum cooling protection when rotated in a clockwise rotation (looking at the front of the alternator when
mounted on the engine). Using 6-Series, XT-Series or AT-Series alternators in reverse (counter-clockwise) rotation
applications may affect alternator cooling and performance. Large case 94, 95, 97, and 98-Series alternators fea
-
ture bi-directional fans, which are equally effective in normal or reverse rotation applications.
GROUNDING
Alternator models designated as Isolated Ground (IG) feature an independent ground terminal that’s isolated from
the alternator case. Isolated Ground alternators are used in applications where the engine is not desired to be a
part of the grounding system. This is commonplace in steel or aluminum hull boats, or with engines that depend
on sophisticated electronic ignition systems. In other applications, isolated grounding simply ensures that the al
-
ternator is sufficiently connected to system ground. The alternator’s ground cable should be the same size as the
alternator’s positive output cable.
12-VOLT CABLE SIZE CHART
Length/Ft.
5
10
15
20
25
30
40
50
75
Amps
75
8
6
4
2
2
1
1/0 2/0
4/0
100
8
4
2
2
1
3/0 3/0 4/0
125
6
4
2
1
1/0 3/0 4/0
150
6
2
1
1/0
2/0 3/0 4/0
175
6
2
1
1/0
2/0 3/0 4/0
200
4
2
1/0
2/0
3/0 4/0
225
4
1
1/0
2/0
3/0 4/0
250
2
1
2/0
3/0
4/0
275
2
1
2/0
3/0
4/0
300
2
1/0
3/0
4/0
24-VOLT CABLE SIZE CHART
Length/Ft.
5
10
15
20
25
30
40
50
75
Amps
75
8
6
6
4
2
1
1/0 2/0
4/0
100
8
6
4
2
1
3/0 3/0 4/0
125
6
4
2
1
1/0 3/0 4/0
150
6
4
2
1/0
2/0 3/0 4/0
175
4
2
1
1/0
2/0 3/0 4/0
200
4
2
1/0
2/0
3/0 4/0
225
2
1
1/0
2/0
3/0 4/0
NOTE: Charts are a close approximation to calculations, but are not
intended for engineering use.
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